Intensional Context-Free Grammar




Little, Richard

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The purpose of this dissertation is to develop a new generative grammar, based on the principles of intensional logic. More specifically, the goal is to create a psychologically real grammar model for use in natural language processing. The new grammar consists of a set of context-free rewrite rules tagged with intensional versions. Most generative grammars, such as transformational grammar, lexical functional-grammar and head-driven phrase structure grammar, extend traditional context-free grammars with a mechanism for dealing with contextual information, such as subcategorization of words and agreement between different phrasal elements. In these grammars there is not enough separation between the utterances of a language and the context in which they are uttered. Their models of language seem to assume that context is in some way encapsulated in the words of the language instead of the other way around. In intensional logic, the truth of a statement is considered in the context in which it is uttered, unlike traditional predicate logic in which truth is assigned in a vacuum, regardless of when or where it may have been stated. To date, the application of the principles of intensionality to natural languages has been confined to semantic theory. We remedy this by applying the ideas of intensional logic to syntactic context, resulting in intensional context-free grammar. Our grammar takes full advantage of the simplicity and elegance of context-free grammars while accounting for information that is beyond the sentence itself, in a realistic way. Sentence derivation is entirely encapsulated in the context of its utterance. In fact, for any particular context, the entire language of the grammar is encapsulated in that context. This is evidenced by our proof that the language of an intensional grammar is a set of context-free languages, indexed by context. To further support our claims we design and implement a small fragment of English using the grammar. The English grammar is capable of generating both passive and active sentences that include a subject, verb and up to two optional objects. Furthermore, we have implemented a partial French to English translation system that uses a single language dimension to initiate a translation. This allows us to include multiple languages in one grammar, unlike other systems which must separate the grammars of each language. This result has led this author to believe that we have created a grammar that is a viable candidate for a true Universal Grammar, far exceeding our initial goals.



formal grammars, natural language processing, intensional logic, generative grammar, intensional programming, context-free grammars, computational complexity, denotational semantics