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Generative Grammar

Context Free Grammar (starting point for most modern theories of grammar)

Transformational Grammar

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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

Requirements for a „good“ theory of grammar

Limitationsof CFG

A theory of grammar aims at explaining human lingustic behaviouri.e. how language is processed in the mind.

Of greatest practical importance: how can a grammar capture linguistically significant generalizations.

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Problems with Context Free Grammar (CFG)

CFG overgenerates structures, i.e. also many unacceptable structuresare produced

Reason: CFG fails to detect finer categories

Simple or „old“ CFG rule for VP:

VP V (NP)(NP)

The defendant denied the accusation

The problem disappeared

*The defendant denied

*The teacher disappeared the problem

The teacher handed the student a book

*The teacher handed the student.

*The teacher handed a book

*The teacher handed

e.g. Transitiveness

The verb has finer subcategories:

Intransitive Verb IV: takes no objectTransitive Verb TV: takes 1 objectDitransitive Verb DTV: takes 2 objects

Problems with Context Free Grammar (CFG)

VP V (NP)(NP)

To avoid the problem with Transitiveness the old rule has to be replaced by 3! new rules:

VP IV

VP TV NP

VP DTV NP NP

Consequence: addition of new rules results in redundancy of the theory

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Problems with Context Free Grammar (CFG)

Similar Problem : Transitivity and Agreement

S NP VP

S NPpl VPpl

In „real“ English: Subject - Verb Agreement

The bird_ sings

Birds sing_

*The bird sing

*Birds sing

S NPsg VPsg

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, DTVsi.e. add 1 rule for IVs 2 for TVs and 4 rules vor DTVs

Vp IVsg

VP TVsg NPsgVP TVsg NPpl

VP DTVsg NPsg NPsgVP DTVsg NPsg NPplVP DTV sg NPpl NPsgVP DTV sg NPpl NP pl

REDUNDANCY

CFG here does not allow to treat nouns and verbs as general classes with general propreties

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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

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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 singleTree structure but with a sequence of trees.

This allows generalitzation and avoids proliferation of phrase structure rules

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