Structure of a Lexicon

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Structure of a Lexicon

• Debasri Chakrabarti

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Overview

• Categorial Component a set of rules.
• Lexicon containing a list of all the words in a
  language, together with a specification of their
  idiosyncratic syntactic, semantic, phonological
  and morphological properties.
• Lexicalization Principle attaching lexical
  items under appropriate word-level category nodes.

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Lexical Information

• Categorial Features
• Subcategorization Frames
• Selectional Restrictions
• Thematic Roles

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Categorial Features

• For each item listed in the lexicon the grammar
  must specify which syntactic category it belongs
  to.
• Lexicon should say
• boy is a noun
• dog can be either a noun or a verb
• need can function as a verb, a modal, or a noun
• Lexical entry for boy -V, N

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Categorial Features

• There are four major word level categories
• Verb, Adjective, Noun and Preposition.
• (Chomsky, Amherst Lectures, (1974))
• These can be analyzed as complexes of two binary
  features
• (nominal/ non-nominal)
• (verbal/ non-verbal)

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Categorial Features

• These four major word-classes are broken down in
  the following way
• Verb V, -N Noun -V, N
• Preposition -V, -N Adjective V, N
• Capture supercategorial generalisation, i.e.,
  generalisations which extend across more than one
  category

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Categorial Features

• It is necessary to posit that a given category
  may belong to different categorial subclasses.
• Nouns
• Proper Nouns
• Common Nouns
• Common Nouns
• Count Nouns (can be used with a singular or
  plural determiner)
• Mass Nouns
• Lexical entry for boy -V, N, common, Count

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Subcategorization Frame

• Traditional grammar a given item is said to
  take a particular type of complement
• Recent terminologies an item Subcategorizes a
  particular range of complements
• Why subcategorization frame is needed?

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Subcategorization Frame
S
VP
NP
I
V
NP
V
John
will
Mary
?

1. invite, kill, hit, harm, help
2. come, go, wait, fall

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Subcategorization Frame

• Subcategorization Frame does not depend on the
  meaning
• This is a kind of idiosyncratic information
• Example,
• I shall await your instruction.
• I shall wait your instruction.
• It should be included in the lexicon

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Intransitive Verbs

• Intransitive verbs subcategorize zero
  complements
• Two different devices for expressing this
• a. come Categorial Features V, -N
• Subcategorization Frame Ø
• b. come Categorial Features V, -N
• Subcategorization Frame

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Transitive Verbs

• Transitive verbs subcategorize complements
• kill Categorial Features V, -N
• Subcategorization Frame NP

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Subcategorization Frame

• How to specify the Subcategorization Frame for a
  verb which can occur both in transitive and
  intransitive structure?
• John ate.
• John ate rice.
• eat
• Categorial Features V, -N
• Subcategorization Frame

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Ditransitive verbs

• Subset of transitive verbs
• Takes two complements
• Example,
• John gave Mary a book.
• The postman handed me a parcel.
• give Categorial Features V, -N
• Subcategorization Frame NP NP

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Prepositional Complement

• Different Verbs take different PP complement
  headed by different Prepositions
• Example
• I defer to/at/on/by/with your suggestion.
• I put the book on/about/with the table.
• I can rely on/by/to /at/with you.
• rely Categorial Features V, -N
• Subcategorization Frame PP(on)
  NP

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Nouns and Adjectives

• Nouns and Adjectives can also take PP Complements
  obligatorily
• Example
• His reliance on/at/to/by/with her help
• His reliance
• Mary is fond of/at/to/by/with John.
• Mary is fond.
• reliance Categorial Features -V, N
• Subcategorization Frame
  PP(on)
• fond Categorial Features V, N
• Subcategorization Frame PP(of)

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Prepositions

• Prepositions also permit a particular range of
  categories as their complement.
• Example
• I havent seen him since the party.
• I havent seen him since the party began.
• He left during the party.
• He left during the party was still going on.
• since Categorial Features -V, -N
• Subcategorization Frame
  
• during Categorial Features -V, -N
  
• Subcategorization Frame
  NP

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Selectional Restrictions

• Semantic restrictions on the choice of
  expressions within a given category which can
  occupy a given sentence position.
• Differences between Subcategorization Frame and
  Selectional Restrictions are
• Subcategorization Frames are syntactic in nature
• Selectional Restrictions are purely semantic
• Verbs do not Subcategorize their Subjects
• Verbs impose Selectional Restrictions on their
  choice of Subject

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Selectional Restrictions

• murder Categorial Features V, -N
• Subcategorization Frame
  NP
• murdered
• John, knife, tree, lion
• Sam, knife, tree, lion
• Example,
• John murdered Sam.
• John murdered the knife.
• John murdered the lion.

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Selectional Restrictions

• John murdered the tree.
• The knife murdered Sam.
• The lion murdered Sam.
• murder requires both Human Subject and Object.
• murder
• Categorial Features V, -N
• Subcategorization Frame NP
• Selectional Restrictions ltHUMAN HUMANgt

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Thematic Roles

• Each Argument (i.e., Subject or Complement) of a
  predicate bears a particular thematic role.
  (Gruber(1965), Fillmore(1968a) and Jackendoff
  (1972))
• These are also known as theta-role or ?-role.
• The number of ?-roles associated with the Theory
  of Thematic Structure varies somewhat from author
  to author.
• There are some commonly assumed ?-roles.

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Set of Theta Roles

• THEME (or Patient) Entity undergoing some effect
  of an action, (Mary fall down)
• AGENT (or Actor) Instigator of an action, (John
  killed Sam)
• EXPERIENCER Entity experiencing some
  psychological state, (John was happy)
• BENEFACTIVE Entity benefitting from some action
  (John gave a book to Mary)

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Set of Theta Roles

• INSTRUMENT Means by which something comes out
  (John killed Sam with a knife)
• LOCATIVE Place in which something is situated
  or takes place (John put the book on the table)
• GOAL Entity towards which something moves (John
  passed the book to Mary)
• SOURCE Entity from which something moves (John
  took the book from the table)

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Theta Roles

• John gave Mary a book.
• John bears the ?- role AGENT to the verbal
  predicate gave.
• Mary bears the role GOAL.
• Book bears the role THEME.
• A variety of linguistic phenomena can be
  accounted for in a more principled way
• Example, the verb roll can be used both in
  transitive and ergative structure
• Ergative structure is one in which the Object of
  a given transitive verb is used intransitively as
  the Subject of the verb

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Ergative Verbs

• Example,
• John rolled the ball down the hill.
• The ball rolled down the hill.
• In the first sentence the ball is the Object.
• In the second sentence the ball is the Subject.
• The ?-role is same in both the cases, i.e.,
  THEME.

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Summarization

• Lexicon should comprise a set of lexical
  entries-specifying idiosyncratic properties
• Differentiate between subclasses of a category
• Distinguish between intransitive, transitive and
  ditransitive verbs
• Necessity of Selectional Restrictions
• Importance of Thematic Roles

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Suggested Readings

• Andrew Radford, Transformational Grammar A First
  Course, Cambridge Textbooks in Linguistics, 1988.
• Noam Chomsky, Aspects of the Theory of Syntax,
  The MIT Press, 1964.