Lexical functional grammar
Encyclopedia
Lexical functional grammar (LFG) is a grammar framework in theoretical linguistics
, a variety of generative grammar
. It is a type of phrase structure grammar
, as opposed to a dependency 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:
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:
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. Because of this, LFG has been used as the theoretical basis of various machine translation
tools, such as AppTek
's TranSphere, and the Julietta Research Group's Lekta.
Theoretical linguistics
Theoretical linguistics is the branch of linguistics that is most concerned with developing models of linguistic knowledge. The fields that are generally considered the core of theoretical linguistics are syntax, phonology, morphology, and semantics...
, a variety of generative grammar
Generative grammar
In theoretical linguistics, generative grammar refers to a particular approach to the study of syntax. A generative grammar of a language attempts to give a set of rules that will correctly predict which combinations of words will form grammatical sentences...
. It is a type of phrase structure grammar
Phrase structure grammar
The term phrase structure grammar was originally introduced by Noam Chomsky as the term for grammars as defined by phrase structure rules, i.e. rewrite rules of the type studied previously by Emil Post and Axel Thue...
, as opposed to a dependency grammar
Dependency grammar
Dependency grammar is a class of modern syntactic theories that are all based on the dependency relation and that can be traced back primarily to the work of Lucien Tesnière. Dependency grammars are distinct from phrase structure grammars , since they lack phrasal nodes. Structure is determined by...
. The development of the theory was initiated by Joan Bresnan
Joan Bresnan
Joan Wanda Bresnan is Professor of Linguistics at Stanford University. She is best known as one of the architects of the theoretical framework of Lexical-Functional Grammar....
and Ronald Kaplan
Ronald Kaplan
Ronald M. Kaplan is Chief Scientist and a Principal Researcher at the Powerset division of Microsoft Bing. He is also a Consulting Professor in the Linguistics Department at Stanford University and a Principal of Stanford's Center for the Study of Language and Information...
in the 1970s, in reaction to the direction research in the area of transformational grammar
Transformational grammar
In linguistics, a transformational grammar or transformational-generative grammar is a generative grammar, especially of a natural language, that has been developed in the Chomskyan tradition of phrase structure grammars...
had begun to take. It mainly focuses on syntax
Syntax
In linguistics, syntax is the study of the principles and rules for constructing phrases and sentences in natural languages....
, including its relation with morphology
Morphology (linguistics)
In linguistics, morphology is the identification, analysis and description, in a language, of the structure of morphemes and other linguistic units, such as words, affixes, parts of speech, intonation/stress, or implied context...
and semantics
Semantics
Semantics is the study of meaning. It focuses on the relation between signifiers, such as words, phrases, signs and symbols, and what they stand for, their denotata....
. There has been little LFG work on phonology
Phonology
Phonology is, broadly speaking, the subdiscipline of linguistics concerned with the sounds of language. That is, it is the systematic use of sound to encode meaning in any spoken human language, or the field of linguistics studying this use...
(although ideas from optimality theory
Optimality theory
Optimality theory is a linguistic model proposing that the observed forms of language arise from the interaction between conflicting constraints. OT models grammars as systems that provide mappings from inputs to outputs; typically, the inputs are conceived of as underlying representations, and...
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 structureFeature structureIn phrase structure grammars, such as generalised phrase structure grammar, head-driven phrase structure grammar and lexical functional grammar, a feature structure is essentially a set of attribute-value pairs. For example the attribute named number might have the value singular. The value of an...
. - the structure of syntactic constituents (c-structure). See phrase structure rulesPhrase structure rulesPhrase-structure rules are a way to describe a given language's syntax. They are used to break down a natural language sentence into its constituent parts namely phrasal categories and lexical categories...
, ID/LP grammarID/LP grammarAn ID/LP grammar is a formal grammar that distinguishes immediate dominance constraints from linear precedence constraints. Whereas traditional phrase structure rules incorporate dominance and precedence into a single rule, ID/LP maintains separate rule sets which need not be processed...
.
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
Feature (linguistics)
A feature is a concept applied to several fields of linguistics, typically involving the assignment of binary or unary conditions which act as constraints.-In phonology:...
such as number and tense
Grammatical tense
A tense is a grammatical category that locates a situation in time, to indicate when the situation takes place.Bernard Comrie, Aspect, 1976:6:...
or functional units such as subject
Subject (grammar)
The subject is one of the two main constituents of a clause, according to a tradition that can be tracked back to Aristotle and that is associated with phrase structure grammars; the other constituent is the predicate. According to another tradition, i.e...
, predicate
Predicate (grammar)
There are two competing notions of the predicate in theories of grammar. Traditional grammar tends to view a predicate as one of two main parts of a sentence, the other being the subject, which the predicate modifies. The other understanding of predicates is inspired from work in predicate calculus...
, or object
Object (grammar)
An object in grammar is part of a sentence, and often part of the predicate. It denotes somebody or something involved in the subject's "performance" of the verb. Basically, it is what or whom the verb is acting upon...
.
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 SemanticsGlue SemanticsGlue semantics, or simply Glue is a linguistic theory of semantic composition and the syntax-semantics interface which assumes that meaning composition is constrained by a set of instructions stated within a formal logic, Linear logic...
. - 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
Noam Chomsky
Avram Noam Chomsky is an American linguist, philosopher, cognitive scientist, and activist. He is an Institute Professor and Professor in the Department of Linguistics & Philosophy at MIT, where he has worked for over 50 years. Chomsky has been described as the "father of modern linguistics" and...
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
Non-configurational language
In generative grammar, non-configurational languages are languages in which there is no verb phrase constituent . In configurational languages, the subject of a sentence is outside the VP and the object is inside; in non-configurational languages, since there is no VP constituent, there is no...
, 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
Lexicon
In linguistics, the lexicon of a language is its vocabulary, including its words and expressions. A lexicon is also a synonym of the word thesaurus. More formally, it is a language's inventory of lexemes. Coined in English 1603, the word "lexicon" derives from the Greek "λεξικόν" , neut...
, 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. Because of this, LFG has been used as the theoretical basis of various machine translation
Machine translation
Machine translation, sometimes referred to by the abbreviation MT is a sub-field of computational linguistics that investigates the use of computer software to translate text or speech from one natural language to another.On a basic...
tools, such as AppTek
Apptek
Applications Technology is a U.S. software company specializing in human language technology, headquartered in McLean, Virginia.AppTek's primary focus is on machine translation and automatic speech recognition...
's TranSphere, and the Julietta Research Group's Lekta.
See also
- Head-driven phrase structure grammarHead-driven phrase structure grammarHead-driven phrase structure grammar is a highly lexicalized, non-derivational generative grammar theory developed by Carl Pollard and Ivan Sag. It is the immediate successor to generalized phrase structure grammar. HPSG draws from other fields such as computer science and uses Ferdinand de...
- Relational grammarRelational grammarIn linguistics, Relational Grammar is a syntactic theory which argues that primitive grammatical relations provide the ideal means to state syntactic rules in universal terms. Relational grammar began as an alternative to transformational grammar....
- Tree-adjoining grammarTree-adjoining grammarTree-adjoining grammar is a grammar formalism defined by Aravind Joshi. Tree-adjoining grammars are somewhat similar to context-free grammars, but the elementary unit of rewriting is the tree rather than the symbol...
- Glue SemanticsGlue SemanticsGlue semantics, or simply Glue is a linguistic theory of semantic composition and the syntax-semantics interface which assumes that meaning composition is constrained by a set of instructions stated within a formal logic, Linear logic...
, a theory of the syntax-semantics interface