Semantics

Semantics is the study of how the form of a linguistic expression relates to its meaning.

Linguistic Meaning

Linguistic Meaning

Sense and reference are the two aspects of linguistic meaning.

Sense

A mental representation of a meaning.

unicorn, The queen of the United States, The first person on Mars

Reference

The set of real objects in the word that an utterance refers to.

Multiple senses, same reference: The most populous country in the word, The country that hosted the 2008 Olympics

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Lexical Semantics

Lexical Semantics

Lexical Semantics is a study of the sense and reference of words. Proper names refer to one specific entity. However, common nouns, adjectives, and intransitive verbs refer to sets of entities.

Relationships Between Words

• Homonyms: Words that sound the same, but have totally unrelated meanings. (e.g., two and to)
• Polysemous: A word has multiple, related meanings.
• Hyponym: X is a hyponym of Y if and only if the reference of Y is a superset of the reference of X.
• Hypernym: X is a hypernym of Y if and only if the reference of Y is a subset of the reference of X.
• Synonyms: X and Y are synonyms if and only if they have the same reference.
• Antonyms: X and Y are antonyms if and only if their references contrast in some way.
  • Complementary antonyms: Two words X and Y are complementary antonyms if and only if there is no entity in the reference of both X and Y.
  • Gradable antonyms: Gradable antonyms identify different directions on a scale.
• Meronymy: A part-whole relationship where an individual component makes up part of a larger whole. (e.g., wheel is a meronym of car).

Semantic Ambiguity

• Lexical ambiguity: A word is lexically ambiguous if it has two or more possible meanings in a sentence. (e.g., My bat is one of the best things in the world.)
• Structural ambiguity: A sentence has more than one structures that leads to more than one possible meanings. (e.g., Young men and women dominate the company.)
• Scope ambiguity: There’s more than one way to distribute the NPs doing the action in the sentence. (e.g., in a sentenceFour body builders moved two trucks., the number of trucks could be 8 or 2 in total)

Mind Representation of the Sense of a Word

• Dictionary-Style Definitions: Dictionary definitions are circular.
• Mental Images: different People may get different images for the same word
• Usage-Based Definitions: The sense of a word is defined in terms of the contexts where it can be used.

Composition of Adjectives and Nouns

• Pure intersection The Reference of the Adj+N is the intersection of the reference of the Adj and the reference of the N. (e.g., Healty cow, Blue suit)
• Relative intersection: The Reference of the Adj+N is a subset of the reference of the N, defined by the Adj. (e.g., Tall person, Loud music, Good food)
• Nonintersection: The Reference of the Adj+N combination is not necessarily a subset of the reference of the N. (e.g., alleged crime, potential customer)
• Anti-intersection: The Reference of the Adj+N combination is definitely not a subset of the reference of the N (e.g., fake gun, imitation leather)

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Compositional Semantics

Compositional Semantics

Study of how the meanings of words combine to form the meanings of sentences.

Compositional Meanings

The meaning of a sentence can be figured out by looking up the meanings of the words.

It is raining today is compositional, but It is raining cats and dogs is not compositional.

Sense of a Sentence

The sense of a sentence is a Proposition. The reference of a sentence is its truth value.

Thematic Roles

Thematic Roles

Thematic roles describe the semantic relationships between verbs and their arguments. Violating these semantic requirements leads to semantic anomalies rather than ungrammaticality e.g. *The small train loves chocolate.

Thematic Roles for NP

• Agent: the entity that intentionally performs an action. (e.g., Winnie in Winnie fought the bear.)
• Experiencer: the entity that experiences a psychological state. (e.g., Charles in Charles felt sad about his Discovery.)
• Theme: the entity affected by an action. (e.g., the boulder in I push the boulder with all my might.)
• Benefactive: the entity that benefits from an action. (e.g., us in He wiped the tables clean for us.)
• Source: the entity from which something is moved by performing an action. (e.g., Spain in I traveled from Spain to Italy.)
• Goal: the entity toward which an action is directed. (e.g., Italy in I traveled from Spain to Italy.)
• Instrument: the object in which the action is completed with. (e.g. an axe in I slashed the body up with an axe.)

Thematic Grids

A thematic grid lists these thematic roles in order for a specific verb context.

• Dive: <Agent> (e.g., The puppy dove)
• Devour: <Agent, Theme> (e.g., A big monster devoured the kid)
• Give: <Agent, Theme, Goal> (e.g., Susie gave a bucket to Charlie)
• Borrow: <Agent, Theme, Source> e.g., My dad borrowed $10,000 from me.

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