Lexical functional grammar

Lexical functional grammar (LFG) is a grammar framework in theoretical linguistics, a variety of generative grammar. The development of the theory was initiated by Joan Bresnan and Ronald Kaplan in the 1970s, in reaction to the direction research in the area of transformational grammar had begun to take. It mainly focuses on syntax, including its relation with morphology and semantics. There has been little LFG work on phonology (although ideas from optimality theory have recently been popular in LFG research).

LFG views language as being made up of multiple dimensions of structure. Each of these dimensions is represented as a distinct structure with its own rules, concepts, and form. The primary structures that have figured in LFG research are:

* the representation of grammatical functions (f-structure). See feature structure.
* the structure of syntactic constituents (c-structure). See phrase structure rules.

For example, in the sentence "The old woman eats the falafel", the c-structure analysis is that this is a sentence which is made up of two pieces, a noun phrase (NP) and a verb phrase (VP). The VP is itself made up of two pieces, a verb (V) and another NP. The NPs are also analyzed into their parts. Finally, the bottom of the structure is composed of the words out of which the sentence is constructed. The f-structure analysis, on the other hand, treats the sentence as being composed of attributes, which include features such as number and tense or functional units such as subject, predicate, or object.

There are other structures which are hypothesized in LFG work:

* argument structure (a-structure), a level which represents the number of arguments for a predicate and some aspects of the lexical semantics of these arguments. See theta-role.
* semantic structure (s-structure), a level which represents the meaning of phrases and sentences. See Glue Semantics.
* information structure (i-structure)
* morphological structure (m-structure)
* phonological structure (p-structure)

The various structures can be said to be mutually constraining.

The LFG conception of language differs from Chomskian theories, which have always involved separate levels of constituent structure representation being mapped onto each other sequentially, via transformations. The LFG approach has had particular success with nonconfigurational languages, languages in which the relation between structure and function is less direct than it is in languages like English; for this reason LFG's adherents consider it a more plausible universal model of language.

Another feature of LFG is that grammatical-function changing operations like passivization are said to be lexical. This means that the active-passive relation, for example, is a relation between two types of verb rather than two trees. Active and passive verbs are both listed in the lexicon, and involve alternative mapping of the participants to grammatical functions.

Through the positing of productive processes in the lexicon and the separation of structure and function, LFG is able to account for syntactic patterns without the use of transformations defined over syntactic structure. For example, in a sentence like "What did you see?", where "what" is understood as the object of "see", transformational grammar puts "what" after "see" (the usual position for objects) in "deep structure", and then moves it. LFG analyzes "what" as having two functions: question-focus and object. It occupies the position associated in English with the question-focus function, and the constraints of the language allow it to take on the object function as well.

A central goal in LFG research is to create a model of grammar with a depth which appeals to linguists while at the same time being efficiently parseable and having the rigidity of formalism which computational linguists require.

ee also

* Head-driven phrase structure grammar
* Tree-adjoining grammar
* Glue Semantics, a theory of the syntax-semantics interface

External links

* [http://www.essex.ac.uk/linguistics/lfg/ Lexical Functional Grammar Home Page ]
* [http://cslipublications.stanford.edu/site/ONLN.html Proceedings of the annual LFG conference]

References

*Bresnan, Joan (2001). "Lexical Functional Syntax". Blackwell. ISBN 0-631-20973-5
*Dalrymple, Mary (2001). "Lexical Functional Grammar". No. 42 in Syntax and Semantics Series. New York: Academic Press. ISBN 0126135347
*Falk, Yehuda N. (2001). "Lexical-Functional Grammar: An Introduction to Parallel Constraint-Based Syntax". CSLI. ISBN 1-57586-341-3