Method and apparatus for universal parsing of language5878385
Abstract
A method and apparatus for natural language parsing are described. The invention includes the steps of retrieving an input string, and performing a dictionary look-up for each word in the input string to form a correspondence between each word and a dictionary entry. The dictionary entry provides lexical features of the word. The invention includes the additional step of processing the words in the input string beginning with a last word in the input string and continuing toward the first word in the input string. This step includes the step of associating a selected word in the input string with a word located to the left of the selected word in the input string to form a word phrase. The associating step is performed according to predetermined selection restriction rules. The steps of processing the words and associating a selected word are repeated until all words of the input string have been processed.
Claims
What is claimed is:
1. A computer implemented method for parsing words of an input string, the method comprising the steps of:
a) retrieving the input string;
b) performing a dictionary look-up for each word in the input string to form a correspondence between each word and a dictionary entry in the dictionary, said dictionary entry providing lexical features of the word;
c) processing the words in the input string beginning with a last word in the input string and continuing toward the first word in the input string;
d) said processing of the words in the input string including the steps of associating a selected word in the input string with a word located to the left of the selected word in the input string to form a word phrase, said associating performed according to predetermined selection restriction rules; and
e) repeating steps (c) and (d), processing the words in the input string, until all words of the input string have been processed.
2. A computer implemented method for parsing words of an input string, the method comprising the steps of:
a) retrieving the input string;
b) performing a dictionary look-up for each word in the input string to form a correspondence between each word and a dictionary entry in the dictionary, said dictionary entry providing lexical features of the word;
c) processing the words in the input string beginning with a last word in the input string and continuing toward the first word in the input string;
said processing of the words in the input string including the steps of
e) attaching a selected word in the input string to a preceding word in the input string, said attachment performed if permitted by at least one predetermined selection restriction rule and not performed if not permitted by at least one predetermined selection restriction rule, said attachment of the selected word to the preceding word forming a word phrase, said selection restriction rules based upon predetermined lexical features of the words in the input string;
f) promoting at least one of the selected word and the word phrase in the input string to a next higher lexical value if permitted by at least one promotion restriction rule; and
g) repeating the steps (c) through (f), including attaching and promoting, until all words of the input string have been processed.
3. A computer implemented method for parsing words of an input string, the method comprising the steps of:
a) inputting the input string;
b) performing a dictionary look-up for each word in the input string to form a correspondence between each word and a dictionary entry in the dictionary, said dictionary entries providing lexical features of the word;
c) assigning a first level of strength to each word in the input string, said first level of strength defined by the dictionary entry corresponding the word and identifying a basic grammatical category associated with the word;
d) selecting a word in the input string to process, said selected word corresponding to a last word of the input string;
e) determining if the selected word attaches to an immediately preceding word in the input string, said determination performed according to predetermined selection restriction rules and resulting in one of a successful attachment and an attachment failure;
f) said successful attachment resulting in formation of a word group linking the attached words, said word group assigned one of the first level of strength, a second level of strength, and a third level of strength, said levels of strength defined by the predetermined selection restriction rules;
g) said attachment failure resulting in an attempt to promote the word group to a next higher level of strength, until the word group attains the third level of strength; and
h) selecting the next word in the input string located to the left of the selected word and performing steps (e) through (g) until all words in the input string have been processed.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to language parsers and more specifically to a method and apparatus for natural language parsing of sentences in real time that is universally applicable to other languages and is capable of analyzing the full range of grammar and syntax, manipulating sentences to create other structures, and engaging in question/answer and statement/response repartee in real time.
Since Chomsky (Syntactic Structures. The Hague/Paris: Mouton, 1957), linguists have been grappling with the problem of providing a generative theory of syntax to describe the structure of human language. This endeavor has resulted in a proliferation of syntactic theories, each with a slightly different set of assumptions about the correct characterization of syntax. Such known methods are described in publications such as Government and Binding, Chomsky (1981, 1986), Lexical Functional Grammar, Bresnan (1982) and Kaplan and Bresnan (1982), Categorial Grammar, Oehrle, Bach, and Wheeler (1988), Lexicase of Starosta (1988), Generalized Phrase Structure Grammar, Gazdar, Klein, Pullum, and Sag (1985), and Head-driven Phrase Structure Grammar, Pollard (1984, 1985). (Generalized phrase structure grammars, head grammars, and natural language. Stanford University dissertation. "Phrase structure grammar without metarules." In J. Goldberg, S. Mackaye, and M. Wescoat eds., Proceedings of WCCFL 4. Stanford linguistics association, 246-261.)
However, no theory or method has emerged as a widely accepted formulation that strictly conforms to the requirements of an explicit, generative grammar, nor has any theory or method gained wide acceptance as a truly representative model of the human faculty of language. Furthermore, none of these theories or methods have resulted in framework that can be fully implemented in a computer programming language to produce a viable natural language parser.
In the 1960's Noam Chomsky (Aspects of the Theory of Syntax) argued that it was possible to arrive at a scientific description of human language that was based on empirical investigations and which was based on the same principles as the sciences of chemistry, botany and so on. To do this he proposed a theory of syntax based on the structure of English. He further argued that once one had determined the basic nature of the syntax of one language, it would be possible to apply that theory to the languages of the world and arrive at equally descriptive and scientifically falsifiable descriptions as with those of the original language. Of course, there would be language specific variations that would account for the differences we all perceive in the different languages of the world, but the underlying theory would be one of a "universal grammar" from which all other grammars were derived.
It was subsequently argued that the theories of syntax that were proposed by Chomsky and others could be implemented in a computer program to create a "parser," a grammar analysis device, thereby giving computers many (though not all) of the language abilities possessed by people. It is important to point out the meanings of the words "grammar" and "syntax" as used hereinafter. In some cases the words "grammar" and "syntax" overlap in that they both refer to the structural relationship of words and parts of words that result in phrases, clauses, and sentences. However, in general, "linguistics" refers to formal scientific descriptions of these structural relationships while "grammar" refers to the more ordinary English text book style description of these relationships.
Following Chomsky's lead, since the 1960's and continuing to the present, linguists and computer scientists at major universities and institutions around the world have been struggling to arrive at a theory of syntax that is both capable of fully describing the structures of a language and capable of being implemented in a programming language. To date, the success on both counts has been meager at best. There is currently no single parser or method and no theory of syntax that can adequately accomplish the task. In fact, in judging the known methods based on the actual parsers that have been developed, one can conclude that they are still in their infancy. Known parsers and methods can only handle the simplest sentences and are only applicable to a very small subset of the syntactic and grammatical functions that comprise even one language of the world. In spite of the millions of dollars and hundreds of thousands of man hours that have been spent to solve this problem, computers implementing such known methods can only respond to basic commands. Such grammar checkers and translation devices have only the most rudimentary grammatical abilities. The ability to perform question/answer and statement/response repartee with computers and computer applications is unattainable using known methods. The current inventive method and apparatus, interchangeably referred to as "Attach Alpha" (also referred to as "Attach .alpha.") or the theory of Attach Alpha, is a solution to the above-described problem.
Some of the problems that underlie the lack of success of known methods are due to the fact that no theory of syntax has yet been able to claim wide acceptance as a thorough and complete theory. Known theories and methods are either to complex or too poorly or too vaguely formulated to be implemented in a programming language. Finally, a significant obstacle to the implementation of a theory of grammar in a computer program is the fact that such known theories typically generate hundreds, thousands, and even hundreds of thousands of possible parses of one sentence, leaving the computer and the user unable to choose a correct analysis of a sentence.
Known parsers are severely limited since they cannot sufficiently limit the number of possible parses that they produce. If the number of possible parses are too great, processing time increases to a point where real-time output is impossible. In many known parsers, ambiguity in the input string results in an exponential increase in the number of possible output sentences. For example, the sentence "john does like to put the book in the garage", although quite simple in comparison with common English sentences, can produce over 3,000 parses or combinations of sentences. This can be computed by finding the number of possible interpretations of each of the items in the string and counting the number of sentence combinations. In the above-described sentence, "john", "does", and "to" each have two possible meanings, and "like" has four possible meanings, and so on. The combination of possible parsed sentences quickly increases rendering known parsers essentially inoperative.
Accordingly, it is an object of the present invention to substantially overcome the above-described problems.
It is another object of thc present invention to provide a novel method and apparatus for parsing sentences that is universally applicable to all languages of the world.
It is a further object of the present invention to provide a novel method and apparatus for parsing sentences that is implemented on a known digital computer and operates in real time to analyze and parse complex sentences.
It is also an object of the present invention to provide a novel method and apparatus for parsing sentences that significantly reduces the number of parse combinations analyzed, rendering such analysis feasible on a computer.
It is still an object of the present invention to provide a novel method for parsing sentences that strictly limits all structure to that which can be stated in terms of the attachment of two items proceeding from the smallest items upwards toward the completed sentence.
SUMMARY OF THE INVENTION
The disadvantages of present natural language parsers are substantially overcome with the present invention by providing a novel method and apparatus for natural language parsing.
The present inventive method is a syntactic parser developed from a novel theory of syntax, and includes specialized algorithms and parsing strategies that have been used to implement the theory in a computer program. The parser and the theory of syntax are unique in that the theory is applicable to all of the problems of syntax and grammar of a language. As noted above, the theory referred to as "Attach Alpha," and described in detail herein, is the underlying framework for the present inventive method and apparatus. Accordingly, the phrase "method and apparatus" in reference to the novel invention may be referred to interchangeably as "Attach Alpha" or "the parser," hereinafter.
One specific embodiment of the novel method is available for the English language, but may be easily be applied to all languages with minor adjustments. More importantly, all of the theoretical mechanisms used in the theory are easily implemented in a programming language. Thus, the parser is capable of analyzing the full range of grammar and syntax as well as manipulating sentences to create other structures.
Further, the novel parsing method is capable of question/answer and statement/response repartee in real time. The novel parsing method is many times faster than current computer based implementations and operates at higher speeds than all known parsers, particularly when parsing sentences having up to 12 or 15 words with one or two internal clauses. Such a significant increase in processing speed results because the novel parsing method has significantly reduced the problem of analyzing the hundreds, thousands, and hundreds of thousands of possible parses for individual sentences that result from using known parsers and theories of language. No known parsers can successfully perform the functions described herein and no known parsers can fully process an input string in real time, as such parsers fall victim to the hundreds and thousands of possible parses that result when such known parsing algorithms are executed.
The present theory and method has initially been applied to English, but the same theory and method, with minor modifications, is applicable to all of the other languages of the world. For example "minor modifications" mean such simple changes such as respecifying the order of adjectives (e.g. the adjective before the noun in English and other Germanic languages, but the adjective after the noun in romance languages) to more complex matters such as the association of pronouns and reflexives with their antecedents or the association of topics, question words, and other displaced items with their correct role in the sentence.
The grammar analysis, the theoretical mechanisms of the theory that underlie the parser, and the parsing strategies and algorithms described herein may be successfully implemented in a fully operational embodiment using known digital computers appropriately programmed in a selected programming language. The above-identified items provide the unique ability to permit real language interactions with computers and computer applications as well as significant improvements in speed, accuracy, scope, and thoroughness of all grammar analysis problems.
The inventive method and apparatus includes four broad areas: 1) the parser which includes many subroutines and functions that operate on a sentence to perform linguistic and grammatical evaluations, manipulations, and question/answer and statement/response repartee; 2) the theoretical mechanisms based on the theory of Attach Alpha which underlie the parser and its functions and which will be used with minor modifications for other languages of the world; 3) parsing strategies and parsing algorithms, and 4) the series of features and strategies used to manage the dictionaries.
Currently, according to a specific embodiment, a 60,000 word dictionary is used. However, the parser would function properly with much larger or with much smaller dictionaries. Dictionaries are modified to meet the requirements of the present theory and method. Modifications to the dictionary and or the addition or subtraction of lexical features can have profound effects on the operation of the parser. For this reason, the particular nature of the dictionary is unique.
Based on the present inventive method and apparatus, the ability exists to analyze the full range of English grammar and syntax to create much improved grammar checkers, translation devices, foreign language and linguistics tutoring applications, language interactive products, and the like. The theory and inventive mechanisms described herein can be readily adapted to handle any of the world's five thousand (and more) languages. Note that the description included herein frequently refers to the English language. This is done for reasons of illustration only.
The fact the present method and apparatus can handle the full range of grammatical and syntactic phenomena means that a significant improvement can be brought to all software that currently requires grammar analysis of any sort. Additionally, the present method and apparatus can open a new field of language interactivity where real-language question/answer and statement response repartee based on the analysis of grammar is possible.
More specifically, the method and apparatus for natural language parsing according to one specific embodiment of the present invention includes the steps of a) retrieving the input string; b) performing a dictionary look-up for each word in the input string to form a correspondence between each word and a dictionary entry in the dictionary, the dictionary entry providing lexical features of the word; c) processing the words in the input string beginning with a last word in the input string and continuing toward the first word in the input string; d) the processing of the words in the input string including the steps of associating a selected word in the input string with a word located to the left of the selected word in the input string to form a word phrase, said associating performed according to predetermined selection restriction riles; and e) repeating steps (c) and (d), processing the words in the input string, until all words of the input string have been processed.
An another specific embodiment, the steps include a) retrieving the input string; b) performing a dictionary look-up for each word in the input string to form a correspondence between each word and a dictionary entry in the dictionary, the dictionary entry providing lexical features of the word; c) processing the words in the input string beginning with a last word in the input string and continuing toward the first word in the input string; the processing of the words in the input string including the steps of e) attaching a selected word in the input string to a preceding word in the input string, the attachment performed if permitted by at least one predetermined selection restriction rule and not performed if not permitted by at least one predetermined selection restriction rule, the attachment of the selected word to the preceding word forming a word phrase, the selection restriction rules based upon predetermined lexical features of the words in the input string; f) promoting the selected word or the word phrase in the input string to a next higher lexical value if permitted by at least one promotion restriction rule; and repeating the steps (c) through (f), including attaching and promoting, until all words of the input string have been processed.
An another specific embodiment, the steps include of: a) inputting the input string; b) performing a dictionary look-up for each word in the input string to form a correspondence between each word and a dictionary entry in the dictionary, the dictionary entries providing lexical features of the word; c) assigning a first level of strength to each word in the input string, the first level of strength defined by the dictionary entry corresponding the word and identifying a basic grammatical category associated with the word; d) selecting a word in the input string to process, the selected word corresponding to a last word of the input string; e) determining if the selected word attaches to an immediately preceding word in the input string, the determination performed according to predetermined selection restriction rules and resulting in a successful attachment or an attachment failure; f) the successful attachment resulting in formation of a word group linking the attached words, the word group assigned either the first level of strength, a second level of strength, or a third level of strength, the levels of strength defined by the predetermined selection restriction rules; g) the attachment failure resulting in an attempt to promote the word group to a next higher level of strength, until the word group attains the third level of strength; and h) selecting the next word in the input string located to the left of the selected word and performing steps (e) through (g) until all words in the input string have been processed.
BRIEF DESCRIPTION OF THE DRAWINGS
The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof may best be understood by reference to the following description in conjunction with the accompanying drawings.
FIG. 1 is a specific illustration of a block diagram of a computer system according to a preferred embodiment of the present invention;
FIG. 2 is a flowchart of a specific embodiment of a parser according to the present invention, illustrating a Main Overview Routine of the method;
FIG. 3 is a flowchart of a specific embodiment of a parser according to the present invention, particularly illustrating a Dictionary Look-Up subroutine;
FIG. 4 is a flowchart of a specific embodiment of a parser according to the present invention, particularly illustrating a Main Sequence One subroutine;
FIG. 5 is a flowchart of a specific embodiment of a parser according to the present invention, particularly illustrating a Main Sequence Two subroutine;
FIGS. 6A-6D are pictorial representations showing how words or items of a sentence are linked and organized;
FIG. 7 is a flowchart of a specific embodiment of a parser according to the present invention, particularly illustrating a Main Sequence Three subroutine;
FIG. 8 is a flowchart of a specific embodiment of a parser according to the present invention, particularly illustrating detailed steps of an Attach-Subcategories subroutine;
FIG. 9 is a flowchart of a specific embodiment of a parser according to the present invention, particularly illustrating detailed steps of an Attach/promote subroutine;
FIG. 10 is a flowchart of a specific embodiment of a parser according to the present invention, particularly illustrating detailed steps of an Evaluate-Verb subroutine; and
FIGS. 11-12 are flowcharts illustrating a specific embodiment of a parser according to the present invention, particularly showing syntactic, grammatic, and manipulation type subroutines and functions.
DETAILED DESCRIPTION
The present method is implemented as parser in a known digital computer and preferably uses a standard WINDOWS.RTM. interface to demonstrate the functions described herein. However, any suitable interface or operating system may be used, such as Unix, Microsoft WINDOWS.RTM. 95, WINDOWS.RTM. 3.1 WINDOWS.RTM. NT, IBM OS2.RTM., MACINTOSH OS, and the like, or non-windows operating systems, such as Microsoft DOS.RTM.. Such know digital computers may be IBM compatible computers, Macintosh compatible computers, and the like. However, the present novel method and apparatus is not limited to personal computer type machines and may, for example, be ported to mini-computers and mainframe computers. Preferably, the software embodied in the novel method and apparatus is written in the object oriented language of C++ and compiled on Borland C++ compiler Version 4.5. However, any suitable computer language and compiles may be used.
Referring now to FIG. 1, a block diagram of a known computer system is shown which may represent the preferred embodiment of the present invention. However, the preferred embodiment may be practiced on computer systems having alternate configurations, as are known in the art. FIG. 1 illustrates some of the basic components of such a computer system, but is not meant to exclude other components or to imply that such components are necessarily discreet. The computer system 10 includes a bus or other communication means 12 for communicating information, a processing means 14 coupled to the bus for processing information, a random access memory 16 (RAM), commonly referred to as main memory, coupled to the bus for storing information and instructions for the processor, and a read only memory 18 (ROM) or other static storage device coupled to the bus for storing static information and instructions for the processor.
Other devices coupled to the bus 12 include, for example, a data storage device 20, such as a magnetic or optical disk drive for storing information and instructions, an alpha-numeric input device 22 for communicating information and command selections to the processor 14, a curser control device 24, such as a mouse, track ball, curser control keys, and the like, for controlling the curser and communicating information and command selections to the processor, a display device 26 for displaying data input and output, and voice recognition or voice input device 28 for converting speech into text to be supplied to the processor. A scanner 30 may also be coupled to the computer system 10 through the bus 12.
In one specific embodiment of the present invention, the parser is implemented on a known digital computer, and requires about one megabyte of RAM and 400 kilobytes of disk space. The dictionary includes about 60,000 words and occupies about two megabytes of disk space.
With respect to processing an input sentence, computer users want to use real language to interact with computers (with both speech and text). In order to do this, a computer or the embodiment of the parser must recognize questions as questions, statements as statements, correct tense, negative/affirmative statements, and so on. In addition, the parser must be able to manipulate sentences; for example, to make questions from statements, passives from actives, and so on. To recognize and manipulate such structures, the parser first requires the ability to identify parts of speech, parts of the sentence, sentence type (question, statement, etc), and so on.
Because of the theory of syntax, Attach Alpha, that underlies the present inventive method and apparatus, and because of the novel parsing strategies and algorithms described herein, the parser or inventive method does not fall prey to the prohibitively excessive numbers of possible parses that currently stand as a major obstacle to the creation of a parser that can operate in feasible manner on a known computer.
With the above logic in mind, the novel method described herein is embodied in a parser having the ability to do the following significant processes: The parser receives an input string, such as a sentence or grouping of words and: 1) labels part of speech (noun, adjective, verb, etc.), 2) labels parts of the sentence (subjects, objects, and so on), 3) changes active to passive and passive to active, when directed to do so, 4) formulates yes/no questions, and wh-word (who, what, when, where) type questions, 5) labels sentence type, 6) labels tense, 7) labels clauses, 8) identifies part of speech, and 9) checks punctuation, when directed to do so. In addition, there are background processes that create tree diagrams and labeled bracketing diagrams of all the parses that are tried.
The fact that all of the above is successfully performed implies that the parser described herein successfully handles all the grammatical problems of the English language (and of course other languages) because all such problems are merely variations of the syntactic functions that have been described. The parser typically processes sentences of twelve to fifteen words in length having two or three clauses, in real time. Although longer or more complex clauses may slightly slow the processing longer sentences may still be successfully processed in real time. For purposes of illustration, the output of two sentences generated by the parser according to the novel method and apparatus are presented below and are labeled "Sentence Number One," and "Sentence Number Two."
Sentence number #1: John gave Mary a book
Parts of Speech identified:
"John" is a proper noun.
"gave" is a verb.
"Mary" is a proper noun.
"a" is an indefinite article.
"book" is a noun.
Parts of Sentence identified:
"John" is the subject of "gave."
"a book" is the direct object of "gave."
Passive to Active:
Conversion to active not necessary.
Active to Passive:
Mary was given a book by John
Statement to Yes/No Question:
Did John give Mary a book?
Statement to Wh Question:
Who gave Mary a book?
Whom did John give a book?
What did John give Mary?
Sentence Type:
This sentence is simple.
This is a statement.
Clauses:
No internal clauses
Tense:
Simple Past.
Punctuation:
No special Punctuation necessary.
Sentence number #2: The student whom Mary likes is reading a book Sentence
Parts of Speech:
"the" is a definite article.
"student" is a noun.
"whom" is a wh word.
"Mary" is a proper noun.
"likes" is a verb.
"is" is a verb.
"reading" is a verb.
"a" is an indefinite article.
"book" is a noun.
Parts of Sentence:
"whom" is the object of the verb "likes."
"Mary" is the subject of the verb "likes."
"the student whom Mary likes" is the subject of "is reading."
"a book" is the object of "is reading."
Passive to Active:
Conversion to active not necessary.
Active to Passive:
A book is being read by the student whom Mary likes.
Statement to Yes/No Question:
is the student whom Mary likes reading a book?
Statement to Wh Question:
Who is reading a book?
what is the student whom Mary likes reading?
Sentence Type:
This sentence is complex.
This is a statement.
Clauses:
Whom Mary likes: is an adjective clause modifying "the student."
The adjective clause is simple present.
Tense:
Present progressive.
Punctuation:
No special Punctuation necessary.
One example of punctuation problems solved by the inventive method and apparatus is shown below:
Input:
Because John likes reading he is a student.
Punctuation Check Output:
Because John likes reading, he is a student.
The above examples represent the output of the parser for purposes of illustration. There are many more functions that are not necessarily illustrated by the above examples. All of the basic functions of English syntax, universal grammar, and what is referred to as "standard English grammar" are provided herein.
The parser includes three main routines and many subroutines and functions, as will be described in greater detail hereinafter. Within these routines, subroutines, and functions are contained the theoretical mechanisms of the theory of Attach Alpha. This detailed description of the invention is divided into two sections for purposes of illustration, as follows: 1) the theory of Attach Alpha, and 2) a description of the parser, including a description of the flowcharts, and a description of parsing strategies and algorithms.
The theory of Attach Alpha.
1. The present inventive method demonstrates that by beginning with a theory of phrase structure which is rigidly limited to a step by step process of attachment of lexical items into larger words, phrases, and sentences, it is possible to provide a theory of syntax that is simpler and more general than current theories of syntax and which does not require deep structure, movement, deletion, or insertion. Further, the theoretical machinery required for this novel theory is much more restricted than that required by current theories. The many miscellaneous theoretical subcomponents such as c-command, barriers, subjacency, the Empty Category Principle, Government, Proper Government, Lexical Government, etc., as is known in the art, are either not required in the present inventive method or fall out from other subcomponents which arc included in the present inventive theory and method. Finally, all the theoretical mechanisms of Attach Alpha that underlie the present inventive method can be easily implemented in a variety of programming languages.
The present framework requires only one empty category and seven theoretical mechanisms, as follows: 1) rules of attachment, 2) a series of selection restrictions and subcategorizations that constrain the application of Attach .alpha. and determine the category, bar level, and lexical features of the item created by Attach .alpha., 3) a principle to account for the assignment of bar levels in intermediate and maximal structures, 4) a description of the completion of the process of attachment, 5) a description of theta role assignment and interpretation, where "interpretation" of theta roles refers to the process by which N2s are associated with empty categories in order to receive a theta role, 6) the principles which describe the coindexing requirements of non-referential expressions, and 7) the morphological principle of locality referred to as the Immediate Dominance Condition. Also, the seven above-described mechanisms, with minor language specific changes in parameters, are the same in all languages of the world and constitute the full set of theoretical mechanisms necessary to account for the syntax of the languages of the world.
After providing a description of phrase structure, uses of the above-described theoretical devices are illustrated along with a description of several major principles and unique definitions of terms to provide an account of the following phenomena: 1) the assignment of theta roles and empty categories in sentences in which arguments are displaced from the position specified in the theta grid, such as questions with sentence initial wh words, Tough Movement sentences, topicalized sentences, relative clauses, and Cleft and Pseudo-Cleft sentences (also included are restrictions on such displaced arguments such as Pied Piping and the Complex NP constraint), 2) the assignment and interpretation of theta roles in missing constituent sentences such as Control sentences, 3) Parasitic Gap sentences, 4) Island Conditions, 5) the That Trace Effect, 6) the variable presence of overt subjects in infinitival phrases, 7) the coreference requirements of reflexives, reciprocals, and pronouns, and 8) Strong and Weak Crossover Effects.
For convenience and for consistency of reference to prior art literature, the terminology of the Government and Binding theory will be used in reference to the above-described phenomena. One significant point of departure for the present theory is in the theory of phrase structure in which all structure results from the sequential attachment of two items which proceeds from lexical items into larger words, phrases, and sentences, without external devices to constrain the possible trees, such as X-bar theory or phrase structure rules.
In a manner that is consistent with evidence from polysynthetic languages, such as Eskimo languages and nonconfigurational languages, such as Warlpiri, the theory underlying the present inventive method and apparatus proposes that all morphological and syntactic structure is essentially the result of one unitary process which allows lexical items to attach to either other lexical items or to phrases, depending on subcateorizations and selectional restrictions in a manner that is not constrained by a rigid boundary between morphology and syntax. That is, all structure is the result of the successive attachment of lexical items into complex words, phrases, and sentences which begins with items chosen from the lexicon (dictionary) and proceeds upwards to completed sentences.
Unlike known theories of syntax which limit the number of possible syntactic strings by means of different top-down phrase structure formulations in a manner that precedes downwards from the largest possible item e.g., phrase or sentence (S) to the smallest possible item e.g., lexical items or dictionary definitions, the present theory strictly limits all structure to that which can be stated in terms of the attachment of two items proceeding from the smallest items upwards to completed sentences. The term "top down" structure, as used herein, means all theoretical devices or rules that cannot be applied in a literal step-by-step fashion from lexical items to completed sentences, and which must be applied as "well-formedness" conditions on possible strings. The term "bottom up" structure, as used herein, means any theory that builds all structure from a literal series of statements about attachments. Chomsky (The view from Building 20: Essays in Linguistics, Keyser: 1993) presents a theory that claims to be bottom up. However, the X-bar theory still operates as a well-formedness condition on completed strings. Thus, this version of Chomsky's theory is not rigidly bottom-up. If Chomsky's theory could predict the bar levels as the process of attachment proceeded, it would be closer to a bottom up theory-but this is not the case. In fact, the present inventive Attach .alpha. theory underlying the method described herein is the only theory of syntax with accounts for the creation of all structure in terms of bottom up directionality. In other words, instead of generating abstract tree structures that must be lexically filled, this grammar creates all structure directly in a single operation.
Categorical Grammar generally refers to the application of rules which create structure in terms that begin from the bottom and proceed upwards. However, the complex formulae they provide, such as the combinatory rules cited in Steedman (1987), `Categorial Grammars and Parasitic Gaps.` Natural Language and Linguistic Theory 5:403-40.) cannot be applied as literal statements of a sequence of attachments, and therefor must be taken as well-formedness constraints on possible structure. For example, the rule that specifies the attachments for a transitive verb is given in (i), shown immediately below, where a "/" (forward slash) indicates a rightward attachment and a ".backslash." (backward slash) indicates a leftward attachment.
(i) (S.backslash.NP)/NP where S is the sentence level and NP is the noun phrase or N2 level.
The derivation of (i) proceeds upwards, beginning with /NP, to the completed phrase or sentence (S). However, such rules can be applied literally only in those cases when there are no adjuncts attached before the subject is attached. If adjunct arguments are attached, the subcategorization has to be interrupted partially through, in order to allow the application of the rules that attach adjuncts. Then, the subcategorization must be reactivated from where it left off after the attachment of the adjuncts.
Since it is not possible for such subcategorizations to be treated as a literal statement of attachments, it must instead be regarded as a well formedness condition on possible structure. As the sentences in (ii), shown immediately below, indicate, subcategorization frames do not generally allow interruptions. The asterisk indicate an error or incorrect sentence.
(ii) Double Objects
1. A. John gave a book to Mary at 5 o'clock.
B. John gave Mary a book at 5 o'clock.
2. A. *John gave at 5 o'clock a book to Mary.
B. *John gave at 5 o'clock Mary a book.
3. A. *John gave a book at 5 o'clock to Mary.
B. *John gave Mary at 5 o'clock a book.
(iii) Transitive verbs
1. John ate an apple greedily.
2. *John ate greedily an apple.
(ii) Verbs with two complements.
1. John gladly put the car in the garage.
2. *John put gladly the car in the garage.
3. *John put the car gladly in the garage.
Operations, such as the interpretation of empty categories and the evaluation of coindexing requirements for non-referential expressions, are evaluative measures that are applied after the creation of structure. They play no role in creating structures.
The present theory of Attach Alpha underlying the inventive method includes of two major aspects: one that creates structures and one the evaluates structures. Using this basic system to provide a software implemented parser, it is possible to analyze, evaluate, and manipulate sentences in a manner that permits real-time use of real language with computers and computer applications. The two aspects of creation and evaluation of structure are accomplished using eleven points of universal grammar. Each of these points is unique and their use in concert is unique in the present inventive method. The following is a brief overview of each of the eleven points of the present inventive method.
1. Attachment. Any constituent X attaches to any other constituent, as specified in the selection restrictions.
2. Promotion; Promotion after attachment: a) an X0 that immediately dominates another X0 is promoted to an X1; b) an unattached item is promoted by 1 (2 is maximal).
3. Specifier attachment. Items attached at the X1 level are specifiers. X2s are completed by X0 specifiers (e.g. D0s are X0 specifiers). A-domains are completed by X2 specifiers (possessive N2s and nonsubcategorized wh words are X2 specifiers).
4. Argument (A-) domain. An A-domain consists of any N or V head and its arguments.
5. Terminal Argument. A terminal argument is either the first or last required argument attached to an A-domain.
6. Required arguments. Subcategorized and theta marked arguments are attached as stipulated in the lexical entries of the dictionary. An empty category (e.c.) is attached is there is no overt item present for theta role assignment.
7. Nonrequired arguments. All nonrequired arguments must be attached to the independent A-domain of their head.
8. The Immediate dominance Condition. A selection restrictions can refer to the lexical category it selects plus the nodes immediately dominated by the category.
9. Independent. A nonsubcategorized item is independent.
10. Interpretation. Interpretation of e.c.s. begins when all attachment is completed, or when a topic (a nontheta marked N2 modifier in a final argument) is attached. Interpretation begins with the first e.c. attachment:
a) an e.c. is interpreted with a nontheta marked final N2 attached to or within its smallest independent A-Domain;
b) in ›-finite! clauses: an e.c. is interpreted with the nearest available N2.
11. Coindexing restriction.
a) An r/r must corefer with terminal arguments in the smallest A-domain in which it is included, and (if available) a higher terminal.
b) A pronoun cannot corefer with a coargument (a coargument=an argument of the same head) in the same A-domain.
c) An r-expression cannot corefer with items within its smallest independent argument.
d) A possessive cannot corefer with nonterminal arguments or N2s in nonterminal arguments.
The Dictionary
The dictionary in an important and integral part of the implementation of the parser. Words or entries are "looked-up" and lexical information is returned. The first feature of the dictionary entry is called the "lexical" feature and refers to basic syntactic information, such as whether the word is plural or singular, whether it is a participle or not, and the basic part of speech, such as nouns, verbs, adjectives, adverb, etc. For example, the lexical features associated with the noun "John" may include masculine gender, singular member, and count.
The second feature refers to what type of structures can follow all verbs, and in some cases, nouns. For example, a transitive verb is followed by an object, as illustrated in the sentence "John ate a sandwich." In this sentence a ditransitive verb is followed by two objects, as in the sentence "John gave Mary a book." This second feature in the dictionary entry is referred to as the subcategorization frame.
The third feature is called the "theta-grid" and lists the "theta-roles" that a verb assigns. Entries in the theta-grid only exist for verb entries. The theta-role provides the relationship of an item to the verb. For example, the subject of the sentence "John ate a sandwich" is "John," and its relationship to the verb is that of "agent" or "doer" of the action. The word "sandwich" is the object and its role is that of "theme" or "receiver of the action." At first view, this may appear unnecessary since we already have the terms subject and verb in the first and second features of the dictionary. However, it is clear from the passive version of the above sentence, "a sandwich was eaten by John," that the position of the subject and the verb have been reversed while the roles of "doer" and "receiver of action" have not been reversed. Thus, theta-role is the relationship of an item to a verb or preposition and the theta-grid is the list of those roles in the dictionary.
The terms that may be assigned to the theta-roles are: agent, theme, compliment, goal, locative, time, instrument, and complement. However, this list is not exhaustive and other terms may be added or deleted where applicable without affecting the basic operation of the novel method. The agent is the doer of action, the theme is the person or thing affected by the action, the goal is the person or thing toward whom the action is directed, the locative is the location where the action occurs, and the time is the time at which the act takes place, if applicable. The instrument is the tool or means by which the action is performed and the complement is used for complements of linking verbs. For each word in the dictionary, the part of speech corresponding to that word is defined as part of the lexical features of the word. A letter and number identifier are given to identify the part of speech as follows:
Noun (N0: common noun; N2: proper nouns, pronouns or acronyms)
Question words (N2W: who, what, when, where, why, etc.)
Preposition (P0, P3 not originally in dictionary, created during processing to handle particles)
Verb (V0)
Determiner (D0: the, a, this, that, etc.)
Adjective (A0)
Adverb (B0, B2)
Subordinating conjunction (S0)
Coordinating conjunction (K0)
Transition (T0)
Auxiliary (a subclass of V0)
Modal (included in auxiliary)
Complement (C0: that)
Gerund (G0)
Infinitive marker (F0: to)
For each of the above-defined items or entries in the dictionary, each item may be given one of three levels of strength as processing of the phrase or sentences proceeds. All grammatical categories, such as adjective, verb, noun, and the like, can be described as having an associated basic, intermediate, or maximal strength represented by X0, X1, or X2, also known as X-bar levels or bar levels. For example, a noun (N) may be represented as N0, N1, or N2 representing basic strength, intermediate strength, and maximal strength, respectively. In general, the "0" level or strength are dictionary items or entries. Each part of speech is generally associated with the basic level or "0" level of strength prior to processing by various routine. The "1" level or strength are intermediate to base words and phrases, and the "2" level or strength represents full phrases or sentences.
For example, the dictionary may be a 60,000 word dictionary version of the COMLEX.RTM. dictionary available from the Linguistic Data Consortium at the University of Pennsylvania. However, any suitable commercially available linguistics-oriented dictionary may serve as the base dictionary, subject to modification to permit object-oriented software access to the data contained therein.
Any theory of structure based entirely on the successive attachment of lexical items into larger units will not result in a framework that conforms to the requirements of the X-bar theory. Accordingly, in known theories, the X-bar theory must to be added to guarantee that only the required structures are generated. For example, the attachment of an adjective to a noun does not in itself produce an N1 level. Also, the attachment of an argument to a verb does not itself produce a V1. It is necessary to consult the X-bar framework to determine the bar levels that result from particular attachments. Further, from the point of view of the sequential attachment of lexical items in known theories and methods, there is nothing to prevent attachments that violate X-bar theory, such as the attachment of a determiner to an NP, rather than to an N1. Only an external "top down" structural framework, such as the present inventive method and apparatus, can overcome such problems. The present inventive method and theory of Attach Alpha underlying the method avoids this difficulty by using a principle that generates intermediate categories and bar levels along with the generation of structure. This principle, called Promotion, is presented in greater detail in subsection (5) entitled Promotion.
The theory described herein generates all structure by the rule of Attach .alpha. which creates structure through the successive attachments of lexical items to create complex words, phrases, and sentences based on the requirements of the selection restrictions. The rule of Attach .alpha. also makes it possible to remove the need for the double listing of these requirements in both the Word Formation Rules and the lexical entries of the individual affixes. Thus, use of the rule of Attach .alpha. reduces the amount of theoretical machinery necessary for the theory of morphology.
Just as the rule of "move .alpha." (plus accompanying constraints) presented in Chomsky ("Conditions on rules of grammar," Linguistics Analysis 2:303-351, 1976) makes it possible to do without the massive accumulation of transformations that characterized earlier versions of Chomsky's theory, so the rule of "Attach .alpha." (with accompanying selection restrictions) makes it possible to do without the wide array of constraints and principles that characterizes current theories of syntax and known methods associated therewith. The rule of Attach .alpha. is constrained by selection restrictions such as subcategorizations, and Categorial selection restrictions which make statements about the general properties of allowable attachments such as, "adjectives attach to nouns," or "determiners attach to N1", as will be described in greater detail hereinafter. Further, by requiring that all structure be specified in terms of a step by step process of attachment, both the generation and analysis of strings is significantly simplified. Attach .alpha. is described below in greater detail in (1).
(1) Attach .alpha.
The items to which Attach .alpha. applies are either lexical items or items that have been created by previous applications of Attach .alpha.. The node that results from the attachment of the two items is given the category, bar level, and lexical features of the head. In general, the head refers to the item being modified. A head is determined by looking at the selection restriction and determining which item will give the lexical features to the newly created item. Thus, if the adjective `big` is attached to the noun `dog,` the result is the item `big dog.` Since `big dog` acts as a noun, the newly created item is a noun and, thus in the selection restriction, the noun is said to be head. Nonheads in a selection restriction are called modifiers. The head of the newly created item and the order of attachment (head first or head last) are stated as part of the selection restrictions. There are two kinds of selection restrictions, those which provide the distribution facts of categories, as shown below in subsection (2A), and standard subcategorizations as shown below in subsection (b) for the verb put. An extensive list of selection restrictions is provided in subsection 6 entitled Selection Restrictions.
(2) A. An adjective attaches to the left of the noun it modifies.
B. put ›--N2 P2! (where N2 is the noun phrase and P2 is the prepositional phrase)???
Selection restrictions generally specify the attachment of one item to another item. However, verbal subcategorizations are selection restrictions that often specify more than the attachment of just one item. In order for such subcategorizations to conform to the requirements of bottom up structure, each item of the subcategorizations must be attached sequentially without interruption. That is, if a subcategorization is not treated as a literal statement of allowable attachments, it becomes a well-formedness condition on completed trees, which violates the bottom up form of structure of the current theory. Theoretically, Attach .alpha. can attach any lexical item to any other lexical item or any item formed by previous applications of Attach .alpha., but the selectional restrictions and subcategorizations determine whether or not particular attachments are grammatical. Given the restricted notion of phrase structure in this theory, all possible attachments must be described in a selectional restriction or the attachment is not licensed.
Example (2), shown immediately below, illustrates the basic principles of attachment and promotion in a simple sentence:
EXAMPLE (2) ##STR1##
In the above sentence, "the" is a determiner D0, "big", "black", and "hungry" are adjectives A0, and "dog" is a noun N0. First, attachment is attempted using the selection restriction that permits an A0 to attach to an N0 forming an N0. The attachment of "hungry" to "dog" forms a level N0. As attachment continues in a right to left manner, the A0 corresponding to "black" and "big", respectively, are sequentially attached forming three levels of N0 above the initial level of N0 formed by the lexical entry corresponding to "dog."
Attachment finally fails when D0 is encountered because no selection restriction permits attachment of a D0 to an N0. Once attachment fails, promotion is attempted. Note that three occurrences of N0 dominate the lowest level N0. Promotion rules specify that an X0 (meaning, any identified part of grammar, such as N (noun), V (verb), A (adjective)) that immediately dominates another X0 is promoted by one level to an X1 level. Accordingly, each dominating N0 is promoted to level N1 leaving three level N1s dominating the level N0. This "dominance-type" promotion rule may be referred to as Promotion part A, and is always attempted before attempting Promotion part B, described hereinafter.
Once promotion is complete, attachment is again attempted. Given the current levels indicated in the example, there is a selection restriction that permits a D0 ("the") to attach to an N1 to form a level N1. Next, attachment continues but fails because there are no more words in the string to process. Accordingly, promotion is again attempted. In this iteration, the above-described "dominance-type" or Promotion part A cannot be applied since the proper condition does not exist. Therefore, Promotion part B is attempted. Promotion part B specifies that an unattached item is promoted by one level, up to the maximum level. Therefore, the unattached N1 is promoted to a level N2. The N2 level indicates a complete phrase or sentence (S) has been fully parsed.
Example (3), shown immediately below, illustrates the process of attachment in a simple sentence. The final and intermediate bar levels are not completely specified in (3). Bar levels are discussed in Section 3 and arc further illustrated in example (6).
EXAMPLE (3) ##STR2##
Since this method allows no other means of phrase formation other than Attach .alpha., all arguments must be fully formed before they can be attached to the verb. Thus, in sentence illustrated in example (3), John put the car in the garage, the N2, the car, must be created before it can be attached to put. Similarly, P, in the garage, must be created before it can be attached to the phrase, put the car. The attachments of lexical items that produce the arguments of the verb must also be specified in selection restrictions or subcategorization frames.
In this method, tense is attached directly to a verb as an affix. There are no INFL, TNS, or AGR nodes, as exist in the well known Government and Binding theory. The attachment of every verbal argument results in the creation of a V0 because the V0 is the head. As with other attachments, the lexical features of the head are assigned to the V0 that is created by the application of Attach .alpha..
Auxiliary verbs are attached to a main verb as any other attachment, as illustrated in example (4) immediately below. (Intermediate categories are not included in trees until shown in example (6)).
EXAMPLE (4) ##STR3##
In the sentence of example (4), all the auxiliaries are attached as modifiers of the main verb (see selection restriction (Cviii) in Section 6). The main verb is the head, so the V0 category of the head and the lexical features of that head (including subcategorization frame and theta grid) become the category and the lexical features for the item created by the attachment of the auxiliary to the main verb. Thus, been is attached to waiting, and have is attached to been waiting and so on. During this process, all theta grid, subcategorization frame, and other lexical features are the same for the newly created item as they are for the head (the main verb). Thus, in example (4), the lexical features for the uppermost V0 are identical to those of the lexical entry of the main verb. As auxiliary verbs, the verbs have, do, and be are attached by selection restrictions: i.e., they do not have subcategorization frames and do not assign theta roles. As main verbs, the verb be assigns a "theme" theta role to its left while both the verb have and the verb do assign an "agent" to its left and a "theme" to its right. Theta role assignment is more fully discussed in Section 7.1.
2. Lexical entries
In some cases, lexical items need to specify the hierarchical strength or `bar level` of a category as part of the lexical entry. Some lexical items are listed as 0, or level 0, and some as -2. The entries preceded by a minus sign are not to be confused with the dictionary entries without the minus sign, or X-bar levels. The minus sign indicates manipulation or identification within a word, such as "un" or other prefixes. The minus sign is developed as the parser processes words and phrases and is only a temporary indicator. This is necessary to capture generalizations about the distribution of lexical items in morphology. For example, it is necessary to distinguish between those items which can only serve as input to a morphological selection restriction (such as some affixes) and those items which can also serve as an item in the syntax (as is the case with most words). Those items which can serve as items in syntax are listed in the lexicon as level 0s while those which cannot are listed in the lexicon as level -2. Level -1 reserved for intermediate categories generated during the process of attachment. The present method accepts this distinction and extends it to syntax as well. That is, just as there are two category strengths in morphology (the 0s and -2s), there are two category strengths in phrase structure as well, that is, the level 0s, already described for morphology, and the level 2s which are phrasal categories. The level 0s of morphology are level 0s in syntax as well.
The level 2s of syntax are distinguished from level 0s in a manner similar to the distinction between 0s and -2s. That is, lexical items that can serve as items in the syntax but cannot serve as objects of a morphological selection are level 2s. Lexical items that cannot serve as morphological objects are: pronouns, anaphors, wh words, and proper nouns. Since these items cannot be selected in a morphological selection restriction, they cannot be 0s. Therefore, they must be level 1s or 2s. Since phrases need an intermediate level as in morphology, the level 1 is reserved to mark intermediate categories in the syntax and a level 2 is used to mark those categories which cannot serve as morphological objects. Besides the fact that the 2s cannot be used as morphological objects, they also have other properties in common as well. For example, level 2s cannot have specifiers attached to them (e.g. you cannot attach a determiner to proper nouns or pronouns) and 2s can serve as phrases without further attachments.
3. Intermediate categories
Intermediate categories and maximal categories are created by a principle called `Promotion` which creates the intermediate level 1 categories from level 0s, and maximal categories from level 1s. Level 2 is the maximal category or bar level. This principle is presented in (5) immediately below.
EXAMPLE (5)
Promotion
Rule 5A: A level 0 that immediately dominates another level 0 of the same category is promoted to a level 1. (Also referred to a Promotion part A).
Rule 5B: An item left unattached after the application of Attach .alpha. is promoted by one level. (Also referred to as Promotion part B). Note that a level 0 is promoted to level 1 and a level 1 is promoted to level 2, where level 2 is the maximum level possible.
The rule of Attach .alpha. applies freely as long as it does not violate any selectional restrictions. Attach .alpha. will fail, however, when adjacent items in a string do not conform to selection restrictions. When Attach .alpha. fails, Promotion is attempted. After Promotion is applied, Attach .alpha. is tried again. Example (6), shown immediately below, provides the tree for example (3) (shown above) and includes intermediate and maximal categories formed by the operation of Promotion.
EXAMPLE (6) ##STR4##
The tree in Example (6) indicates the attachments and promotions that are necessary to create the level 2 verb, V2. The arguments of the verb must be formed before they can be attached to the V0. For example, the N2 the car must be formed before it can be attached to the verb put.
The N2, the car, is formed as follows: a D0 must be attached to an N1, so at first no attachments are possible and Attach .alpha. fails. Promotion is then tried which promotes the N0 to the next level, namely, N1. Rule 5A is not applicable so Rule 5B is applied to create an N1 from the N0. Attach .alpha. is tried again and it can be applied to attach the D0 to the N1, creating another N1. Because an N1 does not satisfy the subcategorization of the verb, put, Attach .alpha. fails and Promotion is tried again. Again, Rule 5A, is not applicable. However, Rule 5B can be applied to promote the N1 to an N2. Then attachment to the verb is possible.
The formation of the P level proceeds as follows: the N2, the garage must be formed before it can be attached to the P0. The selection restriction for D0s states they must attach to an N1, so initially the D0 cannot attach to the N0 garage. Since no attachments are possible at this point, Promotion can be tried. Rule 5A is inapplicable because no level 0 categories dominate identical level 0 categories. However, Rule 5B can be applied to create a level N1. Next, the D0 can be attached to the N1 which creates another N1. In a similar manner the P0, in, cannot attach to an N1 and thus, the N1 is promoted to an N2 which allows the attachment of the P0 to an N2. Next, Attach .alpha. is applied to attach the arguments of the verb to the V0 to create a sequence of V0s. After all the arguments are attached to the verb, there are no further possible attachments, so Attach .alpha. fails. When Attach .alpha. fails, Promotion is tried again. Since there are V0s that immediately dominate other V0s. Rule 5A is applied to create a succession of V1s. The lowest V0 is not promoted because it does not immediately dominate another V0. Attach .alpha. is then tried again. There are no possible attachments, so Promotion is tried one more time. Rule 5A is not applicable, so Rule 5B is applied to convert the uppermost V1 into a V2. A sentence is not complete until this last operation of Promotion converts the V1 to a V2. The sentence can then serve as an independent sentence or as an argument of another verb.
Example (7), immediately below, provides a more complex example which illustrates the interaction of morphology and syntax.
EXAMPLE (7) ##STR5##
The attachments necessary to create the sentence illustrated in Example (7) proceed as follows. The affix, un- is attached to the verb, cover. The verb is in the past tense so the affix, ed, is attached to the V0, uncovered. Then, the affix -ion is attached to the verb corrupt in order to create a noun object for the verb, uncover. Verbs subcategorize for X2s, so at first the object, corruption cannot be attached to the verb because it is an N0. Since no attachments are possible at that point (i.e. there are no modifiers of that N0), Promotion (Rules 5A and 5B) can be tried. Rule 5A is not applicable, so Rule 5B can be applied to create an N1. There are still no possible attachments, and Promotion is applied once more to create an N2. This makes the attachment of the object to the verb possible. The complex N2 that constitutes the subject must be completed before it can be attached to the verb.
To create the subject, first the affix, -ion, is attached to the verb, investigate to create a noun. There are no possible attachments at this point, so Promotion Rule 5B is applied until the noun, investigation, is at an N2 level. There are still no possible attachments since the genitive affix does not attach to an N2 on its right. There is also no N2 to the left of the genitive affix, as required by its selection restriction, it is not yet possible to attach the genitive. The noun, board cannot be attached to the determiner because the determiner requires an N1. At this point, Promotion Rule 5B is tried to create an N1 from the N0, board. The N1 can then be attached to the D0 which creates another N1. No attachments are possible, so the N1 is promoted to an N2 according to Rule 5B. At this point, the genitive can be attached to the N2. A genitive attaches to a V1, not a V0, so the N0, investigation, must be promoted to N1 before attachment is possible. At that point, the genitive phrase, the boards investigation can be attached to the verb. The attachment of the subject to the verb creates a V0. There are no further attachments, so the uppermost V0 is promoted to a V1 and then to a V2, according to Rule 5B.
Example (8), immediately below, provides an example from Greenlandic, an Eskimo language in which syntax and morphology are very clearly interrelated. (The abbreviation, ALLAT, refers to allative case marking and the abbreviation, INDIC, refers to indicative mood, the forms illu and kar- are monomorphemic.)
EXAMPLE (8) ##STR6##
Since there is no need to stipulate that all morphological attachments must precede all syntactic attachments, it is possible for words and affixes to be intermixed in a manner that blurs the distinction between words and phrases. This is the case in Example (8) in which the sentence, we are going to his house, is essentially one word in which both syntactic and morphological information are contained.
4. Domains.
The coreference facts of anaphors and the association of empty categories with overt N2s cannot be described without reference to domains; that is, it is necessary to refer to specific structure types within which these principles operate. These structure types are referred to as domains. Note that as used herein, "corefer" or "coreference" involves the reference peculiarities of different types of pronouns. In the sentence "John likes himself," "John" refers to "himself" and "himself" refers to "John." Thus, it is said that "John" and "himself" corefer.
A domain in this theory and method can be a phrase, or a sentence. A phrase is defined simply as any X2, a sentence is a V2. However, for the purpose of delimiting domains, the terms phrase and sentence catnot be distinguished so simply because, as demonstrated in Chomsky's earlier works, phrases with possessive nouns, such as Bob's pictures of himself, constitute a domain that is equivalent to a sentence for the purposes of coreference. The standard explanation of this is that the possessive noun of such phrases acts as a kind of subject, and for that reason, such phrases share certain properties with sentences. Such an analysis is problematic in that it requires the use of the relational notion of `subject` for a structural description. In the present inventive method, the fact that subjects and N2 heads of a possessive phrase form similar domains follows naturally from the definition of domain.
The term `subject` does have a structural definition in the current theory. A subject can be defined as any N2 in ›X2 ›N2 position. This includes heads of possessives and the subjects of sentences. In this theory and inventive method, the term "subject" refers to an N2 in ›X2 ›N2 position.) In this theory, a domain is formed by the attachment of arguments to either an N or V head and is called an `Argument Domain.` Argument domain is defined in example (9) below. The fact that possessive phrases are equivalent to sentences for the purposes of coreference is due to the fact that both structure types are argument domains. There is no need to refer to the relational notion of subject to explain this equivalence. The attachment of arguments to other categories such as P0s and C0s does not form A-domains, because such items are not Ns or Vs.
EXAMPLE (9)
Argument (A)-domain
An A-domain consists of an N or V head and its arguments. The facts of coreference and the interpretation of empty categories also indicate that, in complex phrases and embedded sentences, a single domain can include embedded A-domains.
For example, V2s that are subcategorized by a verb constitute a sub-part of the A-domain formed by that verb, but adjunct V2s (and other adjuncts) which are not subcategorized, are independent. Thus, in Example 10A, shown immediately below, the entire sentence is made up of only one independent A-domain because the embedded V2 is subcategorized. However, in Example 10B, shown below, there are two independent A-domains because there are two nonsubcategorized A-domains. The A-domains in Example 10A and 10B are marked with square brackets.
`Independent`is defined in (11).
Example 10A. ›John believes Sue saw Mary!
Example 10B. ›John believes Sue! ›because she saw Mary!
(11) Independent Item. An independent item is any nonsubcategorized item.
5. Argument Types and Specifiers.
The present theory and inventive method makes the usual distinctions between arguments, complements, and adjuncts where arguments are X2 modifiers of heads; complements are subcategorized arguments; and adjuncts are optional arguments. The present theory and method also uses the terms `specifier` and `topic` as in other theories, but these terms need to be defined in terms of bottom-up structure. One term which is specific to the present theory is `terminal argument` which refers to either the first or last required argument attached to a head. The definitions for specifier, topic, and terminal argument are presented in (12), below.
(12) A. Specifier: Any item attached to an X1 is a specifier.
B. Topic: A topic is a nontheta marked final N2 modifier.
C. Terminal Argument: A terminal argument is either the first or the last required argument (required arguments are either subcategorized or theta marked arguments) attached to an A-domain.
(12A) defines the term `specifier`. As in other theories, a phrase can contain only one specifier, and this specifier must be in final position of the phrase. In terms of bottom up structure, this means that it is possible to attach one and only one specifier. Therefore, besides the absence of further items to be attached, the process of attachment is completed by the attachment of a specifier as described in (13).
(12B) provides the definition for the term "topic." It uses the expression, "final N2 modifier," which means the N2 is the last modifier attached to a string. Cleft sentences can be incorporated into (12B) by modifying the definition of `topic` to include a nontheta marked N2 within a final argument where `final` refers to the last argument to be attached. Sentence (i), immediately below, provides an example of a cleft sentence.
(i) It's these shoes that Bill must wear e
In sentence (i) the N2, these shoes, is a nontheta marked N2 within a final argument. Thus, interpretation of the empty category with that N2 is possible. We use the simpler definition in (12B) for ease of reference.
(13) The completion of the process of attachment. Attachment is `completed` by the attachment of a specifier:
A) an X0 specifier (e.g. a D0) completes a phrase,
B) an X2 specifier (e.g. a possessive N2) completes an A-domain.
The sentences in (14) through (16) illustrate the effects of (13A). (13A) states that a phrase (an X2) is completed by the attachment of an X0 specifier. That is, any X0 which attaches to an X1 will complete a phrase, and no further items can be attached to such an item.
The effects of this on X2s (phrases) is illustrated in (14). Phrases completed by the attachment of a specifier can contain unsatisfied dependencies, as illustrated in (15) and they can serve as items in later attachments as illustrated in (16).
(14) A. ›the big black dog!
B. *my ›the big black dog!
C. *these ›the big black dog!
(15) who did you see ›the pictures of e ! ?
(16) I saw ›the big black dog !
(13B) states that the attachment of an X2 specifier creates a `completed` A-domain. No other attachments can be made beyond that point, and no other argument can be added to that A-domain. This means that all further attachments to that phrase are impossible and arguments cannot be added to that A-domain. That is, arguments cannot be added to a completed A-domain either by attachment or by the interpretation of an empty category with an argument outside that completed A-domain.
In English, possessive N2s and nonsubcategorized wh words are attached at the X1 level to create a completed A-domain. It is important to note that subjects are not specifiers. They are attached to a V0 like any other argument (see (22Cvii) in Section 6). Therefore, they do not prevent the attachment of further arguments. Thus, the attachment of nonsubcategorized wh-words and the heads of possessives complete the process of attachment because they are attached at the X1 level, but subjects which are attached to V0s do not complete the process of attachment, as illustrated in (I).
(i) a. *what does who see e
b. *pictures John's e
c. what does Betty see e
d. these mushrooms Betty might eat e
(This is illustrated in (17) and (19)). Possessives are attached at the N1 level in order to account for the facts in (17).
(17) A. Mary saw John's new house
B. *Mary saw new John's house
C. *Mary saw the John's new house
D. *what did Mary see John's new e
E. *what did you see whose pictures of e
F. Bob's sister's house
(17A) provides a sentence with an acceptable possessive N2 where the possessive is attached finally to the noun head. (17B) and (17C) illustrate that attachment cannot continue after the attachment of the possessive, and (17D) and (17E) illustrate that another argument also cannot be added to a completed A-domain by interpreting an e.c. with an N2 that is outside of it. That is, the attachment of the question word in (17D) and (17E) is unacceptable because an argument has been added to a completed A-domain by associating an e.c. with an e.c. internal to the completed A-domain. (15) above illustrates that, unlike a completed A-domain, a phrase completed by an X0 specifier (e.g. the D0) does not prevent interpretation of an empty category with an argument outside the completed X2.
(17F) seems to be a counter example to this principle in that it appears that the N2, Bob's, has been attached to an N2 that has already been completed by the attachment of the possessive sister's. Attachment of Bob's to sister's house as in (18A) is impossible because sister's is a possessive which attaches to an N1 and completes attachment. However, the sentence in (17F) can be formed by attaching Bob's to sister, and then attaching the possessive `s` to Bob's sister, as in (18B). (The arrows in the trees in (18) indicate the promotions that are necessary before attachment can take place.)
EXAMPLE (18) ##STR7##
The facts of the distribution of nonsubcategorized wh words parallels that of possessive N2s, so it is necessary to attach these as specifiers as well. In general, wh words are attached to a verb by subcategorization frames, but a separate selection restriction is required to attach nonsubcategorized wh words. The selection restriction for nonsubcategorized wh words is given in (19). (20) provides sample sentences.
(19) A nonsubcategorized wh word is attached to the left of the VI it modifies.
(20) A. *what did who give Betty e
B. *who did what did John give e c
C. *why did who leave
D. *these mushrooms who might eat e?
E. *which books did John forget who wrote e?
Attaching an X2 at an X1 level completes an A-domain. Therefore, like the sentences in (18), the statements in (20) are unacceptable because arguments have been added to an A-domain after the attachment of the specifier. The selection restriction in (19) attaches the wh word as a specifier, and thus attachment cannot continue after that point. (13B) requires that no argument can be added to a completed A-domain. Thus, (20E) is unacceptable because a wh word is interpreted with an empty category in an A-domain that was completed by the attachment of a nonsubcategorized wh word. Other languages, such as Italian and Russian, do not parallel English in this regard in that they allow multiple wh words in certain circumstances. This would be the result of different selection restrictions. The interpretation of an e.c. from within a completed argument with an N2 outside that argument constitutes `adding` an argument to that A-domain, which is precluded by (13B).
(12B) defines the term `topic.` In this theory and inventive method, a topic is "a nontheta marked final argument attached to a head." Thus, a fronted wh word and a topic are included in this definition because they are both nontheta marked final N2s attached to a head. However, the head of a relative clause such as what in John knows ›what he likes ! is not a topic because, even though it is a nontheta marked final argument, it is a head: it is not a modifier attached to a head as required by (12B). The importance of this distinction becomes clear in the discussion of the interpretation of e.c.s in Section 7.3.2.
(12C) presents the definition of `terminal argument` a term specific to this theory and inventive method. Terminal arguments are the first and last required (subcategorize or theta marked) arguments attached to a head. For example, in the sentence, who did John give the book e in the restaurant, only the book and John are terminal arguments because they are the first and last required arguments to be attached. The question word, the empty category, and the object of the preposition are not terminal arguments. The N2, Bob's, in Bob's house, is a terminal argument because it is an argument (an X2 modifier) and it is the first argument attached to the head N.
6. Selectional restrictions.
This section presents a list of the lexical items and selection restrictions required for English. These lists are not meant to be exhaustive, but merely a representative sample. Example (21) provides a list of lexical items and (22) provides the selection restrictions.
(21) Lexical items.
A. -2: noncategory assigning affixes, and bound stems.
B. 0: Category assigning affixes, N0s, V0s, A0s, Adv0s, D0s, C0s (such as that and for) and P0s.
C. 2: Pronouns, empty categories, anaphors, wh words, and proper nouns. (The one empty category that is required in this method and theory is an N2, and it is represented by a lower case `e.` Empty categories are not considered to be pronouns , they are equivalent to the referential expressions.)
Lexical entries for verbs, derivational affixes, and some nouns include specific subcategorization frames. Other categories utilize the categorial selection restrictions. Categorial selection restrictions are language specific statements that specify allowable attachments for categories, but subcategorizations are part of an items lexical entry and stipulate required arguments. Subcategorizations are required for not only verbs and affixes, but also for certain noun-plus-argument combinations such as, the professor of chemistry. In such cases the modifier cannot be separated from its head just as a subcategorized complement of a verb cannot be separated from its head because the selectional restrictions are stipulated in the lexical entry. That is, the subcategorization must be satisfied before other selectional restrictions are allowed to apply. This is illustrated in (i) presented immediately below.
(i) A. *a professor from England of chemistry
B *John put the car at 5 o'clock in the garage.
(22) Selection restrictions.
A. Subcategorizations.
Lexical items with complements, such as derivational affixes, verbs, and some nouns have subcategorizations which are specific to each. The item with the subcategorization requirement is the head.
In order for the subcategorization to be satisfied, the subcategorized arguments have to be attached first. If an item is attached to the head before its subcategorization is met, the subcategorization is violated. As stated in footnote 2 (presented after Example 29), this makes it impossible to include subjects as part of the subcategorization. That is, given this strict notion of bottom up theory, if subjects were included in the selectional restriction of a verb as in Categorial Grammars, it would be impossible to ever have VP internal optional arguments because the subject would mandatorily be attached before any optional arguments could be attached. The attachments specified in the subcategorizations must be made first in order to be met at all. Any attachment of an adjunct would interrupt or prevent the implementation of a subcategorization frame. If subcategorizations are allowed to be interrupted they become well formedness conditions that operate on completed strings in violation of the theory of bottom up structure.
B. Selectional restrictions for inflectional affixes.
The descriptions below are part of the definition of the categories and cannot be derived or predicted. The descriptions are based on the facts of distribution.
(i) A genitive -z is attached to the right of the ›+genitive! N2 it modifies.
(ii) A plural -z is attached to the right of the regular ›+plural! N2 it modifies.
(iii) A comparative -er is attached to the right of the ›+comparative! A0 it modifies.
(iv) A superlative -est is attached to the right of the ›+superlative! A0 it modifies.
(v) A third person -z is attached to the right of the third person present indicative of the regular verb it modifies.
C. Selectional restrictions for categories.
(i) A0s attach to the left of the N0s they modify.
(ii) A2s attach to the right of the N0s they modify.
(iii) N2s attach to the right of the P0s they modify.
(iv) P2s attach to the right of the N0s they modify.
(v) Genitive nouns attach to the left of the N1s they modify.
(vi) The complementizer, that, attaches to the left of the V2 that modifies it.
(vii) An X2 attaches to the V0 it modifies.
(viii) An auxiliary or modal verb attaches to the left of the V0 it modifies.
(ix) wh word is attached to the left of the ›V1 it modifies.
The following is an expanded list of selection restrictions. Again, the list is not exhaustive and additional selection restrictions may be added.
Standard Selection Restrictions
A D0 to the left of an N1 creates an N2.
A P0 to the left of an N2 creates a P2.
An N2W to the left of a V2 creates an N2.
An N2W to the left of a V2›N2 creates and N2.
An S0 to the left of a V2 creates a V2.
An S0 to the left of a G2 creates a V2-.
An A0 to the left of an N0 creates an N0.
A P0 to the left of a P2 creates a P2.
An N2 to the left of a V0 creates a V2.
An N0 to the left of an N0 creates an N0.
An N0 to the left of an N0 creates a split*.
A B0 A0=A0.
An N0 to thc left of a P2 creates and N0.
A C0 to the left of a V2 creates a C2.
An N2 to the left of an N1 creates an N1.
An N0 to the left of an N1 creates an N1.
An N0 to the left of a G1 creates a G2.
An N2 to the left of a G1 creates a G2.
A V2 to the left of a K0 creates a V2.
A K0 to the left of a V2 creates a V2.
A V2 to the left of a V2›K0 creates a V2.
A T0 to the left of a V2 creates a V2.
A V2 to the left of a T0 creates a V2.
A V2 to the left of a ›V2›S0 creates a V2.
A V2›S0 to the left of a V2 creates a V2.
A V2 to the left of a V2›T0 creates a V2.
Selection Restriction for Verbs.
A modal attaches to the left of a simple form of the verb.
The helping verb "do" attaches to the left of a simple form of the verb.
The helping verb "be" attaches to the left of a past or present participle.
The helping verb "have" attaches to the left of a past participle.
Selection Restriction for Adverbs.
An adverb of class one attaches to the left of a verb.
An adverb of class two attaches to the left or right of a V2.
An adverb of class three attaches to the left or right of a V2 or to the left of a V0.
The selectional restriction in (Cvii) attaches arguments to verbs. This selection restriction does not specify either left or right attachment because either is acceptable. Embedded sentences and adjuncts are attached to a verb just as any other argument. All the attachments necessary to create the sentential complement must, of course, be completed before an embedded V2 can satisfy the subcategorization requirement of the verb that selects it.
7.1. Theta role assignment and interpretation.
Theta role assignment refers to the association of a theta role of a verb with an argument. Theta role requirements of verbs are specified in the dictionary entry for each verb in the theta grid. The theta grid specifies which theta roles are to be assigned and the positions to which they are assigned. Interpretation refers to the association of an empty category with an overt N2, so the empty category can have a referent. Empty categories are selected in those cases when an overt N2 is not available for attachment in a theta position. An empty category can be seen as a form of place holder for a theta role, and in the process of interpretation, the theta role is associated with an overt referent. In the present theory and inventive method, there is only one empty category, which is represented in a string by a lower case `e.`
(23A) below, describes theta role assignment. Theta role assignment proceeds simultaneously with attachment. As the arguments of a verb are attached, theta roles must be assigned. If there is no overt N2 present for theta role assignment, an e.c. must be attached in the position that is assigned the theta role. The e.c. must later be interpreted with an overt N2, as described in (23B) or the sentence will fail.
(23B) below, describes the interpretation of e.c.s. Interpretation associates e.c.s with overt N2s. Interpretation is the last operation in the creation of a string. An e.c. must be interpreted with: 1) a nontheta marked final N2 (e.g. a topic, a fronted wh word, or the head of a relative clause), or 2) other N2s as in Control sentences. Note that (23Bi) must be tried first; if it can apply, it must apply. (23Bii) is tried next, if (23Bii) can apply it must. (23Bii) is limited to ›-finite! A-domains. As stated in (23B), each independent (nonsubcategorized) A-domain must be interpreted individually. Interpretation begins when an independent A-domain is completed, or when a topic is attached. Interpretation begins with the most deeply embedded empty category and proceeds to the highest. `Most deeply embedded empty category` refers to the e.c. that was the earliest to be attached to the head of an A-domain. For example, in the creation of (i) below, the most deeply embedded empty category is the e.c. farthest to the right because it was the first e.c. attached in constructing the V2: the infinitival complement must be formed before it can be attached to the matrix verb, and the first argument to be attached in the infinitival clause is the e.c. theme. However, in (ii), the most deeply embedded empty category is the one closest to the verb because it was attached to the head before the adjunct containing the other empty category.
(i) who does John want e to work for e
(ii) What did John destroy e before e reading e
(23) Theta role assignment and interpretation.
A. Theta role assignment: All theta roles must be assigned as specified in the theta grid.
B. The interpretation of empty categories: After attachment is completed or a topic is attached, the empty categories of each independent A-domain are interpreted with available (An N2 is `available` only if it has not already been interpreted with an e.c. from the same A-domain.) N2s as follows (The attachment of a topic forces interpretation: The topic must be interpreted with an e.c. that has the same smallest independent A-domain as it.):
(i) An e.c. is interpreted with a nontheta marked final N attached to its smallest independent A-domain.
(ii) (In ›-finite! A-domains) an e.c. is interpreted with the nearest theta marked N2.
Theta grid requirements in this theory and inventive method are absolute. If there is no overt N2 present for theta role assignment, an e.c. must be selected in that position or the sentence will fail. Thus, e.c.s are place holders for theta roles. E.C.s. cannot be attached in positions that are not specified in theta grids, and they cannot be used if an overt item is present for theta role attachment.
Pied Piping and the Left Branch Condition are useful to illustrate the attachment of e.c.s. As described by (23A), (23A) e.c.s will only be attached when there is no overt N2 in a position that is assigned a theta role. The sentences in (i), immediately below, provide examples of the phenomena called `Pied Piping.` The sentences in (ii), immediately below, illustrate the Left Branch Condition.
(i) a. This is the book which I have proofread the preface of e
b. This is the book the preface of which I have proofread e.
In the sentences in (i), above, it is possible to have an e.c. replace either the object of the preposition `of` as in (i(a)), or the entire object of the verb `proofread` as in (i(b)). In this theory and inventive method, all P0s assign theta roles and the P0 of in this case, assigns a `genitive` theta role. Unlike P0s, case markers such as possessive `s`, do not assign theta roles. Thus, in (i(a)) and (i(b)), an e.c. can be selected instead of an overt N2 because the head is a theta role assigner. Later, (23B) will apply to provide the correct interpretation.
The Left Branching Condition describes the fact that an N2 constituent of a larger N2 can not be extracted. Examples are given in (ii).
(ii) a. You saw the president's wife's guard
b. *whose did you see ›N2 e wife's guard !N2
c. *whose wife's did you see ›N2 e guard !N2.
d. whose wife's guard did you see.
The sentences in (iib) and (iic) are unacceptable because it is impossible to get an e.c. in those positions: (23A) states that e.c.s are selected only when there in no overt N2 present for theta role assignment. The possessives `whose` and `wife's` in (ii) are not theta marked arguments so e.c.s are not possible because e.c.s can only occur in theta marked positions.
The current theory and inventive method requires one statement for each of the processes that are governed by interpretation: 1) the interpretation of topics, fronted wh words, and the heads of relative clauses, and 2) the interpretation of N2s in Control type sentences. While the current theory and inventive method require two statements for the interpretation of e.c.s, the current method of interpretation is far less complicated than a theory that requires three types of empty category (e.g. trace, PRO, and pro) plus: lexical government, antecedent government, proper government, c-command, the empty category principle, and the other theoretical devices such a theory entails.
The next two sections described below provide demonstrations of theta role assignment of (23A) (section 7.2.), and the interpretation of empty categories of (23B) (Section 7.3.).
7.2. Theta role assignment of (23A).
Examples (24) and (25) illustrate theta role assignment in a sentence without any empty categories. (24) provides the theta grid for the ditransitive verb give, and (25) provides a sentence that conforms to that theta grid.sup.1.
.sup.1 The facts of Dative Shift indicate that there are two theta grids and two subcategorizations for ditransitive verbs, one which describes sentences such as (ia) and the other for sentences such as (ib).
(i) a. John gave Mary a book.
b. John gave a book to Mary.
Similarly, ergative variations of verbs such as those in (ii) entail an alternate theta grid.
(ii) a. John melted the ice
b. the ice melted
(24) give <agent, .sub.-- theme, goal>
Example (24) specifies that a theme theta role is assigned to the right of the verb and a goal follows. The agent theta role is assigned to an N2 to the left of the verb. Example (25) provides a tree in which theta role assignment has proceeds in an ordinary manner. The empty `<>` grid on the uppermost V2 illustrates that all theta roles have been assigned.
EXAMPLE (25) ##STR8##
Sentence (26) provides an example of the same sentence with an empty category. The theta grid is exhausted on the V1 that dominates Bob gave e to Mary, therefore, there is no theta grid after that point.
EXAMPLE (26) ##STR9##
In sentence of Example (26), the theta grid of (24) would not be satisfied if the empty category were not placed in the theme position of the sentence. The N2, these mushrooms, does not receive a theta role, and therefore must be interpreted. The interpretation of empty categories is presented in the following section (Section 7.3). Sentence (27) provides an example of a passive sentence of a transitive verb.
(27) The criminal was arrested (by the police).
In a passive construction, the past participle of a transitive verb appears with the verb `be,` and a theme theta role is assigned to the N2 in subject position and an agent theta role is not assigned. However, an agent can optionally appear as the object of a `by phrase.` In this theory and inventive method, it is assumed that the past participle which is used for passive constructions does not assign theta roles unlike other forms of the verb. A passive construction is formed by attaching the past participle to the verb `be` like an adjective. The verb `be` as a main verb always assigns a theme theta role to its right. Thus, in passive sentences, the subject always has a theme theta role.sup.2.
.sup.2 Intransitive verbs cannot serve as adjectives in passives because they cannot serve as adjectives in any situation as illustrated in (i).
(i) A. *the slept man
B. *the man was slept
C. *the happened accident
D. *the accident was happened
In a question formed by the attachment of a wh word in subject position, subcategorization frames and theta grids are satisfied with normal word order: neither interpretation nor empty categories are required as illustrated in (29).
EXAMPLE (29) ##STR10##
In those cases in which a nonsubject wh word is attached, there must be an empty category in the sentence in order for the wh word to be associated with a theta role by interpretation as in (30).
EXAMPLE (30) ##STR11##
The assignment of theta roles in (30) proceeds as follows: the theme theta role of the verb is assigned to the empty category and the agent is assigned to John. The wh word is attached without a theta role and must be associated with an empty category through interpretation by (23B). Until interpretation applies, the wh word is a nontheta marked N2. The following section provides a description of the operation of (23B) beginning with the e.c. in sentence (30). A sentence like (31) is impossible because the topic has not been interpreted. The attachment of a topic forces interpretation, and interpretation must apply. If no theta role were assigned as the object of see, the sentence would fail because the wh word could not receive an interpretation.
7.3.1. The Interpretation of empty categories of (23B).
In this section examples of the interpretation of empty categories of (23B) are presented beginning with a discussion of (23Bi). (23Bi) accounts for the interpretation of topics, fronted wh words, Cleft sentences, relative clauses (including Pseudo-clefts), and Parasitic Gap sentences. (23Bi) associates e.c.s with nontheta marked final N2s (topics and the heads of relative clauses). (23Bii) accounts for the interpretation of e.c.s in Control sentences. A discussion of (23Bii) follows in section 7.3.3.
7.3.2. The interpretation of empty categories of (23Bi).
As stated in (23B), interpretation begins when all attachment is completed or when a topic is attached; each independent A-domain is interpreted individually. The lowest e.c. in an independent A-domain is interpreted first, and (23Bi) is tried first. (23Bi) states that an e.c. can be interpreted with a topic.
The e.c. of sentence (30) is interpreted as follows. After attachment is completed, (23B) is tried. (23Bi) must be tried first. It can, and therefore, must apply in this case to associate the e.c. with the topic: (23Bi) can apply in this case because the topic is a nontheta marked final N2 attached to.sup.3 the smallest independent A-domain of the e.c. The process of interpretation associates the nontheta marked final N2 with a theta role, and the e.c. with a referent. (31) provides a sentence in which a fronted wh word (a nontheta marked final N2) is interpreted with the theta role of an e.c. in an embedded sentence. (23Bi) is tried first, and it can and must apply because there is a topic attached to the independent A-domain of the e.c. The entire sentence is the independent A-domain of the e.c. because the embedded V2s are subcategorize. Thus, they are not independent and cannot be interpreted individually.
.sup.3 `Attached to` is used instead of `in` to recognize that (23Bi) can interpret an e.c. with an N2 within the A-domain of an e.c. as with topics or with an N2 adjacent to the A-domain of the e.c. as with a relative clause. The interpretation of e.c.s with the heads of relative clauses and the structure of relative clauses is discussed later in this section.
EXAMPLE (31) ##STR12##
Topicalized sentences such as (32) are interpreted in a similar manner by (23Bi).
EXAMPLE (32)
These mushrooms, I think Betty might eat e.
The theme theta role of the embedded verb in (32) is assigned to the e.c., and these mushrooms, is a nontheta marked final N2 attached to the A-domain of the e.c. The embedded V2 is a subcategorized A-domain, so it is not independent. Since there is a nontheta marked final N2 attached to the independent A-domain of the e.c., (23Bi) can and must apply in this sentence.
The sentences in (33) illustrate that a topicalized sentence cannot appear as an embedded argument of another verb.
EXAMPLE (33)
A. *John knows ›that the ball Mary threw e!
B. *John knows ›what did Bob see e!
The sentences in (33) are unacceptable because, as stipulated in (23B), the attachment of a topic to a V0 triggers interpretation and the end of attachment. That is, the attachment of ball, to Mary threw e and the attachment of who in (33B) triggers interpretation and no further attachment can take place. Thus, the attachment of the V2 as an argument of the higher verb is not possible. Fronted wh words as in (33B) qualify as topics because they are nontheta marked final N2s attached to a head as required by (14B).
Relative clauses such as those in (34) are superficially similar to the sentences in (33), but such sentences are acceptable because the head of a relative clause is not a topic (a nontheta marked final N2 attached to a head). Since the head of a relative clause is not a topic, the formation of a relative clause does not trigger interpretation.
EXAMPLE (34)
A. the students who are university employees can leave early. (restrictive interpretation)
B. the students, who are university employees, can leave early. (nonrestrictive interpretation)
C. the students, university employees, can leave early.
D. the tall students can leave early
E. the student Bob likes e can leave early
The structure of a relative clause requires some clarification. As illustrated in (35), the distribution of relative clauses parallels N2s and not V2s.
EXAMPLE (35)
A. *John likes Bill went to school
B. John likes what Bill did e
C. John likes T.V. because of the movies Mary likes e
D. John likes the school in which he works
That is, a relative clause can serve as object of a verb that does not allow V2 complements as illustrated in (35A) and (35B). Also, an N2 and a relative clause can serve as an object of a preposition as in (35C) and (35D) but a V2 cannot. Thus, a relative clause is an N2, not a V2. Accordingly, the head of the attachment that forms the relative clause must be an N (as stated in section 1 the head of an attachment contributes the category and lexical features to the item that results from the attachment). Since relative clauses and appositives are formed by modifying nouns with V2s (or another N2 as in (34C), it is necessary to conclude that the resulting structures are N2s, not V2s.
A relative clause is formed in English by modifying a noun with a V2. For example, the relative clause in (34A) is formed by modifying the N0, students with the V2 who finished the test. Since the head, students, is an N0, the item formed by this attachment is also an N0. After attachment is completed, Promotion will convert the N0 to an N2.
Examples (34B) and (34C) are similar to (34A), but in these cases the V2 modifies an N2 to form a nonrestrictive relative clause in (34B) and an appositive in (34C). The heads of these attachments are N2s, so the resulting structures are also N2s. The difference between the restrictive relative clause in (34A) and the nonrestrictive relative clause in (34B) is that the former involves the modification of an N0 and the latter involves the modification of an N2.
Obviously, the heads of relative clauses do not qualify as topics since they are heads not modifiers. Therefore, unlike the formation of sentences with topics, the formation of relative clauses does not trigger interpretation. However, in (23Bi), the interpretation statement that interprets e.c.s with topics, can apply to interpret e.c.s with the heads of relative clauses because the heads of relative clauses are nontheta marked Ns attached to the independent A-domain of an e.c.
Since the formation of a relative clause does not theta mark the V2 that modifies the N2 head, the V2 in a relative clause is an independent A-domain. Interpretation of the head of the relative with an e.c. within the V2 that modifies it is possible because the head is a `nontheta marked N attached to its A-domain` as required by (23Bi).sup.4. The relative clause itself may or may not be theta marked., but the N2 head of a relative clause is a nontheta marked final N2, so (23Bi) can apply. (23Bi) is not written for topics; it is written for nontheta marked final Ns, so it can interpret an e.c. with a topic (a nontheta marked final N2 attached to a head) and with the heads of relative clauses, which are also nontheta marked Ns.
.sup.4 In a relative clause such as (34) the independent A-domain of the e.c. is the V2 that contains the e.c. The head of the relative clause is outside of that A-domain. (23Bi) does not require that the nontheta marked N2 be `inside` the A-domain of the e.c. it interprets; it simply requires that the nontheta marked N2 be `attached to` the A-domain of the e.c. The head of a relative clause is attached to the A-domain of the e.c. as required by (23Bi), so interpretation is possible.
To illustrate the difference between relative clauses and topicalized sentences, Example (36) provides two morphologically identical sentences with different syntactic structures: one is a topicalized sentence and the other is a relative clause. (36A), the relative clause construction, is acceptable, but (36B), the topicalized V2 construction, is unacceptable.
EXAMPLE (36)
A. I like ›N2 the man ›V2 Bill saw c!V2!N2
B. I like ›V2 the man Bill saw e!V2
The attachment of the topic in (36B) triggers interpretation and prevents the attachment of the embedded V2 to the verb like. However, in (36A), the nontheta marked final N2 is the head of a relative clause; it is not a topic. Thus, interpretation is not triggered and attachment can continue. After all attachment is completed the head of the relative clause will be interpreted with the e.c. by (23Bi).
EXAMPLE (37)
*John left Bill e complaining about e
Sentence (37) is unacceptable because the attachment of Bill to complaining about constitutes the attachment of a topic which triggers interpretation and prevents all further attachment.
Pseudo-cleft sentences, which involve relative clauses in subject position, such as (38) are interpreted in the same way as the relative clause in (36). That is, the attachment of the wh word head of the relative clause to the V2, John saw e, does not trigger interpretation, so the relative clause can be attached to the verb. After the completion of the entire sentence, interpretation can begin. The subject (a nonsubcategorized argument) is an independent A-domain, so it can be interpreted.sup.5. (23Bi) can apply to the subject to interpret the wh word with the e.c. because there is a nontheta marked final N2 attached to the A-domain of the e.c. The A-domain of the e.c. is the V2, John saw e. If the N2, what, were attached to the V0 as an argument (as is the case with topics) attachment would have to stop.
.sup.5 The subject will not be interpreted until all attachment is completed or a topic is attached. It cannot be interpreted before it is attached to the main verb because interpretation follows the end of all attachment.
EXAMPLE (38)
›what John saw e! was a book
The examples in (39) and (40) are interpreted in a manner similar to Pseudo-Cleft sentences because these also involve relative clauses in subject position.
EXAMPLE (39)
›the hope which spring promises e! is elusive
EXAMPLE (40)
›the man e to talk to e! is Bob!V2
In sentences (39) and (40), the final N is a head of a relative clause. Such attachment does not trigger interpretation, so attachment is not interrupted. Thus, the relative clause can be attached to the verb.
Pseudo-cleft sentences and the sentences in (39) and (40) which involve the interpretation of an N2 in subject position by (23Bi), contrast with the sentences in (41) in which the interpretation of an e.c. internal to a subject is impossible.
(23) predicts the acceptability facts for the sentences in (41) which involve the attachment of a topic to a V0 after the attachment of the subject; that is, in these sentences the nontheta marked final N2 is a topic; it is not the head of a relative clause. It is not possible to attach a topic directly to the subject in (41) because the attachment of a topic would trigger interpretation. As stated above, Pseudo-cleft sentences and other relative clauses in subject position are not precluded because, in Pseudo-cleft sentences, the head of a relative clause is not a topic, and interpretation is not triggered.
EXAMPLE (41)
A. who did e embarrass Bob? (emphatic use of did)
B. *who did ›pictures of e! embarrass Bob?
C. what did John think e would embarrass Bob
D. *who did John think ›pictures of e! would embarrass Bob
E. ›linguistics for you to give up e! would be a shame
Sentences (41A) and (41C) illustrate that an e.c. in subject position can be interpreted with a topic attached to the main verb. (41B), (41D), and (41E) illustrate that an e.c. contained within a subject cannot be interpreted with a topic.
In (41A) and (41C), the smallest independent A-domain of the e.c. is the entire V2. The e.c. is itself a nonsubcategorized N2, but it is not composed of a noun head with arguments, so it does not constitute an A-domain. The smallest independent A-domain of the e.c. is the entire V2, and this V2 has a nontheta marked final N2 attached to it, so (23Bi) can be applied. However, in (41B), (41D), and (41E) the smallest independent A-domain is not the entire V2. Rather, the independent A-domain of the e.c. in these sentences is the subject because the e.c. is an argument of the noun head of the subject.sup.6. The subject is not subcategorize, so it is an independent A-domain. The topic in (41B), (41D), and (41E) is not attached to the independent A-domain of the e.c. as required by (23B), so interpretation is not possible.
.sup.6 The P2, of e ,is an argument of the N0, pictures, in the same way that the P2, with long hair, is an argument of students in students with long hair. In this theory and inventive method, any X2 modifier of a head is an argument of that head.
The statement in (23) also predicts that other nonsubcategorized arguments will allow a bare e.c. to be interpreted with a topic but will not allow an e.c. within a nonsubcategorized argument to be interpreted with a topic because in the former situation the independent A-domain of the e.c. is the entire V2, but in the latter, the independent A-domain of the e.c. is the nonsubcategorized argument. The sentences in (42) illustrate that this is correct.
EXAMPLE (42)
A. who did John see Mary with e?
B. *who did John see Mary with pictures of e?
C. what did John break the window with e?
D. *what did John break the window with a piece of e?
E. *John broke the window with what a piece of e?
In (42A) the e.c. object of the preposition needs to be interpreted. (23) states that an e.c. must be interpreted in its smallest independent A-domain. The preposition is the head of the e.c. However, according to (9) the P does not constitute an A-domain because the P0 is not a noun or a verb. The head to which the P is attached is the verb `see.` The attachment of the P and other arguments to the verb does constitute an A-domain, and this A-domain is not subcategorized, so the smallest independent A-domain of the e.c. in (42A) is that of the verb `see.` There is a nontheta marked N2 attached to that A-domain, so (23Bi) can and must apply.
In (42B) the A-domain of the e.c. is not the P0, `of` because the attachment of an argument to a P0 does not form an A-domain. However, the attachment of the P, `of e.c.` to the noun head `pictures` does create an A-domain. The P0 `with` does not subcategorize.sup.7 `pictures of
.sup.7 N2s are attached to P0s by the selection restriction in (I). There is no need for a subcategorization frame. (I) An N2 is attached to the right of the P0 it modifies. e` so `pictures of e` is independent. Therefore, the smallest independent A-domain of the e.c. in (42B) is the N2, `pictures of e.` This A-domain does not contain a topic, so interpretation by (23) is impossible.
Thus, in sentences (42A) and (42C), interpretation is possible because the smallest independent A-domain of the e.c. is the entire V2 and that V2 has a nontheta marked final N2 attached to it. (42B) and (42D) are unacceptable because the smallest independent A-domain of the e.c. is the object of the P0, which does not contain a nontheta marked final N2.
Parasitic Gap sentences are also explained by the operation of (23Bi). Example (43) provides typical Parasitic Gap sentences in which an adjunct clause contains a gap that corresponds to another gap in a higher sentence.
EXAMPLE (43)
A. ›V2 ›V2 which books did you destroy e!V2 ›P without e reading e!P!V2
B. ›V2 ›V ›N2 John, who we talked to e!N2 ›V2 because we liked e!V2 !V2 V2!
The acceptability of the sentences in (43) depends on the double gap construction as illustrated by the unacceptableness of the sentences in (44) which contain only a single gap.
EXAMPLE (44)
A. *which books did you destroy the books/the house without e reading e?
B. *John who we talked to John/Fred because we liked e
C. *you destroyed the books without e reading e
There are two structures that might be used to describe the facts of Parasitic Gap sentences. The first is one in which the topic is attached to the main verb before attaching the adjunct clause as in (45). The second is one in which the topic is attached to the sentence after the attachment of the adjunct clause as in (46). However, only sentence (46) results in an acceptable sentence.
EXAMPLE (45) ##STR13##
EXAMPLE (46) ##STR14##
The sentence in (45) is unacceptable because attachment has continued after the attachment of the topic in violation of (23B). That is, the adjunct is attached after the attachment of the topic, which prevents all further attachment.
Sentence (46), which provides the tree for (43A), is acceptable and is interpreted as follows: the first e.c. to be interpreted is the object of the main clause. This e.c. is interpreted first because it was the first attached. The adjunct is attached after the main clause is constructed, thus the e.c. in the main clause must have been attached first. It is interpreted with the topic by (23Bi). The next e.c. to be interpreted is the object of the adjunct clause. It is also interpreted with the topic by (23Bi).sup.8. The agent of the adjunct is interpreted last. The agent e.c. cannot be interpreted with the topic by (23Bi). (23B) which requires that all e.c.s within an A-domain be interpreted with available N2s. An N2 is available if it has not already been interpreted with an e.c. in the same A-domain.
.sup.8 The possibility of interpreting more than one e.c. with one final N2 does not occur except with nonsubcategorized clauses because (23) requires that all e.c.s within an A-domain must be interpreted with distinct N2s. Thus, the sentence in (i) does not allow more than one e.c. to be interpreted with the wh word because the e.c.s are all within the same A-domain.
(i) *who did John think e believes saw e
The sentence in (43B) is interpreted in a similar manner. The e.c. object of the adjective clause is interpreted with who by (23Bi), and the e.c. object of liked is also interpreted with who by (23Bi). The interpretation of the two e.c.s with the relative pronoun is possible because each e.c. is in a different independent A-domain: the independent A-domain of the object of talked to is we talked to e; the independent A-domain of the e.c. object of liked is because we liked e.
Sentences in (44A) and (44B) are unacceptable because the topic is not attached to the independent A-domain of its head, as required in Section 4 where, in the discussion of Example (12), it is stated that a nonrequired modifier can be displaced form its head, only if it is attached to the independent A-domain of its head. (44C) is unacceptable because the only interpretation of the e.c. that is possible is semantically anomalous. Specifically, the lowest e.c., the theme of reading, is interpreted with the subject of the main verb rather than with the object because it is the nearest. The distance between an e.c. and the `nearest` available N2 is measured by counting nodes of the tree. It is not measured by looking at proximity within the phonological representation. Example (47) provides the tree for (43C) to illustrate this.
EXAMPLE (47) ##STR15##
By following the nodes of the tree along the path of attachment, it is clear that the subject of the main clause which is separated from the e.c. by five nodes is closer than the object which is separated from the e.c. by seven nodes.
The second e.c., the agent of reading, is interpreted with the theme of the main verb resulting in a semantically anomalous sentence in which the subject of the adjunct and the object of the adjunct are both the books: the anomaly being that the N2, the books, is both the agent doing the `reading` and the object `being read.` It is not possible to interpret the theme of reading with books and the agent with you because that would require that the agent be interpreted first, which violates the order of interpretation stipulated in (23B).
Counting nodes to determine which N2 is the closest to an e.c. for the purposes of interpretation predicts that a single e.c. in an adjunct clause should be interpreted with the subject of the main clause. The sentences in (48) illustrate that this is correct: the e.c. subject of the adjunct clauses in (48) are interpreted with the subject of the main clause.
EXAMPLE (48)
A. John destroyed the books without e reading them
B. John destroyed the books before e coming.
The sentence in (49), however, also involves e.c.s in different independent A-domains.sup.9, but interpretation is not possible.
.sup.9 In cases such as (i) below, the unacceptability of an adjunct clause is caused by the subordinate conjunction that is chosen. In sentence (i), the subordinate conjunction because requires an overt subject for attachment. (See Section 8 for discussion of the IDC which details this sort of selective attachment.)
(i) *which books did John destroy because e reading e
EXAMPLE (49)
*which books did you put back e into the box which contained e?
Example (49) is unacceptable because the e.c. is contained within a V2 that has a wh word attached as a specifier. As stated in (14B), the attachment of a wh word as a specifier completes an A-domain, therefore no further arguments can be added to that A-domain by either attachment or interpretation. Accordingly, the interpretation of the e.c. with which hooks is impossible.sup.10.
.sup.10 Sentences such as those in (i) are unacceptable because they involve empty categories within a subject. See for a discussion.
(i) A. Alex, who friends of e like
B. who did e meeting e surprise you
7.3.3. The interpretation of empty categories of (23Bii).
(23Bii) provides the interpretation of e.c.s in Control sentences. (23Bii) states that, in ›-finite! V2s.sup.11, an e.c. must be interpreted with the nearest theta marked N2. The sentences in (52) provide examples of this phenomena.
.sup.11 The example in (i) indicates that Control-type interpretation is limited to ›-finite! V2s. (ia) and (ib) are identical but interpretation of the e.c. is only possible in (ia) which involves an infinitival complement.
(i) a. John told someone e to work for him
b. *John thinks e works for him
EXAMPLE (52)
A. John needs someone e to work for him
B. John needs someone e to work for e
What needs to be explained in these sentences is that, in (52A) someone is interpreted with the e.c. agent of the embedded sentence, while in (52B) someone is interpreted with the e.c. theme of the preposition of the embedded sentence, and the agent of the embedded sentence is interpreted with John. According to (23Bii), the e.c. in (52A) is interpreted with someone because someone is the nearest nontheta marked final N2. (23Bi) cannot apply because there is no nontheta marked final N2. In (52B) there are two e.c.s to be interpreted. As specified in Section 7, the lowest e.c. must be interpreted first, and thus the e.c. object of for is interpreted with the nearest terminal N2 which is someone. The e.c. in the subject position of (52B) is interpreted next. It cannot be interpreted with someone because someone is not an available N2. That is, it has already been interpreted with an e.c. from the same A-domain. However, (23Bii) can apply to associate the e.c. with the subject of the main verb.
Tough Movement sentences, made famous in earlier works by Chomsky and other linguists, can also be accounted for by (23Bii) without difficulty. Examples of Tough Movement sentences are provided in (53A) and (53B). Tough Movement refers to those adjectives which allow sentential complements as in (53A), and which also allow a pleonastic in subject position of the matrix sentence as in (53B).
EXAMPLE (53)
A. It is tough e to please John.
B. John is tough e to please e.
Theta role assignment in example (53) proceeds as follow. The verb please has an agent theta role and a theme theta role to assign. In (53A) the theme theta role is assigned to John and the agent is assigned to the e.c. The e.c. is interpreted by (23Bii) because (23Bi) cannot apply. In sentence (53B), however, the theme theta role of please is assigned to the empty category and John is in the agent position of the higher sentence. (23Bi) cannot apply to interpret the lowest e.c. because there is no nontheta marked N2, but (23Bii) will interpret it with John. The second e.c. will be interpreted arbitrarily.
(54A) and (54B) demonstrate that not all adjectives that allow sentential subjects also allow pleonastic subjects. This is a result of a difference in the lexical entry, so (54A) and (54B) are not considered within this discussion of the structure of Tough Movement.
EXAMPLE (54)
A. John is eager to please
B. *It is eager to please John
The fact that adjectives like those in (54) do not act like Tough Movement sentences is the result of the fact that there are two classes of adjectives in these sentences: the first type, the Tough Movement type, which can be called endothematic adjectives involve theta roles that are predicated of t h e subject. However, the second type of adjective, those that pattern like eager, can be called exothematic because they involve theta roles that are predicated outside the subject.
8. The Immediate dominance condition.
Both the "That Trace Effect" and the variable presence of subjects in infinitival clauses can be explained by allowing the selection restrictions of those items to refer to the category they require plus the categories they immediately dominate as specified by the Immediate Dominance Condition (IDC). Th e IDC allows the subcategorization of an item to refer to the item selected and to the categories immediately dominated by that item. This principle is merely a revised version of the independently required condition on th e morphological principle of locality.sup.12, and thus results in no extra cost to the grammar. The IDC is presented in (55).
.sup.12 In morphology, the principle of locality restricts access to word internal information. Specifically, the strict version of locality in morphology states that no rule has access to the internal structure of the words they affect. Conditions on the principle of locality such as the Atom Condition of Williams (1981) and the Adjacency Condition of Siegel (1971) allow rules limited access to the internal structure of words. The Immediate Dominance Condition is proposed as an alternative to these earlier conditions.
(55) The Immediate dominance condition.
A selectional restriction can refer to the lexical category for which it selects plus the nodes immediately dominated by that category. For example, the That Trace Effect results from the fact that the complementizer that c |
