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Generative Grammar

Generative Grammar. Context Free Grammar (starting point for most modern theories of grammar). Transformational Grammar. Requirements for a „good“ theory of grammar. Master the infinity of language Be able to explain ambiguities: a string of words can be put together in more than one way

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Generative Grammar

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  1. Generative Grammar Context Free Grammar (starting point for most modern theories of grammar) Transformational Grammar

  2. Requirements for a „good“ theory of grammar Master the infinity of language Be able to explain ambiguities: a string of words can be put together in more than one way Capture generalizations of natural language Be as non-redundant as possible Limitations of CFG A theory of grammar aims at explaining human lingustic behaviour i.e. how language is processed in the mind. Of greatest practical importance: how can a grammar capture linguistically significant generalizations.

  3. Problems with Context Free Grammar (CFG) CFG overgenerates structures, i.e. also many unacceptable structures are produced e.g. Transitiveness Reason: CFG fails to detect finer categories The defendant denied the accusation The problem disappeared *The defendant denied *The teacher disappeared the problem Simple or „old“ CFG rule for VP: VP V (NP)(NP) The verb has finer subcategories: Intransitive Verb IV: takes no object Transitive Verb TV: takes 1 object Ditransitive Verb DTV: takes 2 objects The teacher handed the student a book *The teacher handed the student. *The teacher handed a book *The teacher handed

  4. Problems with Context Free Grammar (CFG) To avoid the problem with Transitiveness the old rule has to be replaced by 3! new rules: VP IV VP V (NP)(NP) VP TV NP VP DTV NPNP Consequence: addition of new rules results in redundancy of the theory

  5. Problems with Context Free Grammar (CFG) Similar Problem : Transitivity and Agreement In „real“ English: Subject - Verb Agreement Vp IVsg VP TVsg NPsg VP TVsg NPpl VP DTVsg NPsg NPsg VP DTVsg NPsg NPpl VP DTV sg NPpl NPsg VP DTV sg NPpl NP pl The bird_ sings Birds sing_ *The bird sing *Birds sing S NPsg VPsg S NP VP S NPpl VPpl since marking is on head noun and head verb, all phrases containing N and V have to be expanded. Example for VPsg: agreement must be mached for IVs, TVs, DTVs i.e. add 1 rule for IVs 2 for TVs and 4 rules vor DTVs REDUNDANCY CFG here does not allow to treat nouns and verbs as general classes with general propreties

  6. Problems with Context Free Grammar (CFG) Heads CFG does not account for the fact that natural language consists of Headed structures, e.g.. that some structures are more natural than others Head: The lexical category (e.g. a verb) that determines the category of the phrase (e.g. VP) E.g. CFG would accept such a (overgenerated) rule : VP P NP CFG categories are arbitrary (e.g. no distinction between Subject and Object) Headedness is a general property of many natural language structures, CFG fails to describe these generalizations

  7. Transformational Grammar as a further improvement of CFG Transformational Grammar (Noam Chomsky) Introduction of Transformation rules which allow to transform one structure (e.g. tree ) into another Example for a transformational operation: The sun is shining and Is the sun shining? In Transformational Grammar each sentence is associated not with a single Tree structure but with a sequence of trees. This allows generalitzation and avoids proliferation of phrase structure rules

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