Lexical-Functional Grammar

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Lexical-Functional Grammar

What is Lexical-Functional Grammar?

Lexical functional grammar (LFG) is a constraint-based grammar framework in theoretical linguistics. It posits two separate levels of syntactic structure, a phrase structure grammar representation of word order and constituency, and a representation of grammatical functions such as subject and object, similar to dependency grammar. 

The development of the theory was initiated by Joan Bresnan and Ronald Kaplan in the 1970s, in reaction to the theory of transformational grammar which was current in the late 1970s. It mainly focuses on syntax, including its relation to morphology and semantics. There has been little LFG work on phonology (although ideas from optimality theory have recently been popular in LFG research).

lexical functional grammar
Source: Semantic Scholar

What is functional grammar example?

Functional grammar has many concepts, so it is not easy to provide a clear and ordered explanation of them. Different books arrange the concepts in different orders. Those charts, tables, or paradigms, plus considerable terminology, look terrible for new learners. 

In traditional grammar, there are 10 parts of speech: 

  • Noun 
  • Verb 
  • Adjective
  • Adverb
  • Pronoun
  • Number 
  • Article
  • Preposition
  • Conjunction
  • Interjection 
examples of traditional grammar

Then each of these ten classes can be divided into subcategories based on their functions.  In functional grammar, these classes of words do not disappear. 

However, functional grammar places English words into four big groups: 

  • Noun group
  • Verb group 
  • Adjective group
  • Prepositional group
segregation of traditional grammar

In addition, traditional grammar analyzes a sentence structure into subject, predicate, object, attributive, adverbial, and complement, while functional grammar gives a clause different functional labels depending on three kinds of meta-functions.

From these two examples, we can see that functional grammar has its own characteristics. To serve its communicative purpose, its concepts are quite different from traditional grammar. Based on current books on functional grammar, its key concepts include functions and systems, hierarchical ranking of units, word order, word groups, functions of the sentence, theme, mood, transitivity, and the clause complex. 

What are lexical and functional phrases?

Lexical words all have clear meanings that you could describe to someone. They’re also all nouns, which is one type of lexical word. 

Functional, or grammatical, words are the ones that it’s hard to define their meaning, but they have some grammatical function in the sentence.

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What’s the difference between lexical and grammatical?

Lexical meaning is dominant in content words, whereas grammatical meaning is dominant in function words, but in neither is grammatical meaning absent. Grammatical words include prepositions, modals and auxiliary verbs, pronouns, articles, conjunctions, and some adverbs.

What is the lexical structure of grammar?

A C# program consists of one or more source files, known formally as compilation units (Compilation units). A source file is an ordered sequence of Unicode characters. Source files typically have a one-to-one correspondence with files in a file system, but this correspondence is not required. For maximal portability, it is recommended that files in a file system be encoded with the UTF-8 encoding.

Conceptually speaking, a program is compiled using three steps:

  • Transformation, which converts a file from a particular character repertoire and encoding scheme into a sequence of Unicode characters.
  • Lexical analysis, which translates a stream of Unicode input characters into a stream of tokens.
  • Syntactic analysis, which translates the stream of tokens into executable code.

What is LFG in NLP?

Lexical-Functional Grammar is one of the hottest areas in the field of NLP. LFG includes two basic forms: c-structure and f-structure. The differences in languages may occur in their structural representation, while it may keep using identical syntactic functions.

Lexical-Functional Grammar plays a vital role in the area of Natural Language Processing. LFG is considered as the constraint-based philosophy of grammar. C-structure and F-structure are the two basic forms of LFG.

What are the structures of Lexical Functional Grammar?

Lexical Functional Grammar 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). 
  • The structure of syntactic constituents (c-structure). 

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 that are hypothesized in LFG work:

  • Argument structure (a-structure), a level that 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 that represents the meaning of phrases and sentences. See Glue Semantics.
  • Information structure (i-structure)
  • Morphological structure (m-structure)
  • Phonological structure (p-structure)

How are lexical rules written?

A lexical rule is in a form of syntactic rule used within many theories of natural language syntax. These rules alter the argument structures of lexical items (for example verbs and declensions) in order to alter their combinatory properties.

Lexical rules affect in particular specific word classes and morphemes. Moreover, they may have exceptions, do not apply across word boundaries, and can only apply to underlying forms.

An example of a lexical rule in spoken English is the deletion of /n/. This rule applies in damn and autumn, but not in hymnal. Because the rule of n-deletion apparently needs information about the grammatical status of the word, it can only be lexical.

What is the difference between lexical class and functional class?

  • Lexical words include things like nouns and verbs and are generally the open-class items in the language. These are words that can be easily added to the language, e.g., Selfie.
  • It is considered that one of the important properties of these functional categories that determine the difference between grammars of different languages.
  • Words that belong to lexical categories are semantically rich and contribute primarily to the meaning of the sentence.
  • Functional items are generally closed-class words. Words in these categories have strict grammatical functions which generally cannot have new words added.
  • Categories that express content (Nouns, Verbs, Adjective, Adverbs)
  • Categories that connect the sentence together. (Articles, Prepositions, Pronounces etc…)

What are the five types of Lexical Verbs?

5 types of lexical verbs

Lexical verbs are the action words in a sentence. They fall into multiple categories and can show the subject’s action or express a state of being.

1. Linking Verbs

Linking verbs connects both the subject and the adjective/ information. Linking verbs often depict states of being or something at the moment. Here’s an example: “The water became yellow.” In this case, became is the linking verb because it connects the description (yellow) back to the subject (water). Other instances of linking verbs include appear, remain, and to be.

2. Transitive and Intransitive Verbs

A transitive verb denotes action towards a direct object receiving that action. On the other hand, Intransitive verbs express action but don’t affect a direct object. An example of the transitive verb is "Kim walks to church". Walks is the lexical verb of the sentence and is transitive. "Kim dances", is an example of an intransitive verb because dances is the lexical verb here not directed towards a direct object. 

3. Regular and Irregular Main Verbs

The difference between regular and irregular verbs is the way their ending changes when they turn to the past tense. Regular verbs in the past tense often end with -ed. Irregular verbs don’t change similarly. 

For example, if we change the tense of this sentence "She bakes a cake" to past tense, the sentence would become "She baked cake". 

Where, for irregular verb the sentence "Jhonny catches the ball" would be changed to "Jhonny caught the ball". Thereby 'Bake' is a regular verb and 'Catch' is an example of an irregular verb. 

4. Dynamic and Static Main Verbs

Dynamic verbs simply express action. For example, "Maria's tire busted". Here, the verb busted was an action. Where on the other side, static verbs describe a situation or state rather than an action. Prefer, surprise, and include are examples of static verbs. For example, “The busted tire scared Maria.” In this case, scared describes how the tire affects Maria more than what it physically does.

5. Auxiliary Verbs

Auxiliary verbs help lexical verbs sometimes to express degrees of time and mood. But the auxiliary verbs are considered lexical verbs. Will, might, can, and need are all comes under the category of helping verbs. In the sentence, “I might go out,” might is the helping verb. It adds intensity to the lexical verb, go.

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