Folie 1

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