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Linguistic Essentials

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Parts of Speech and Morphology

Parts of Speech correspond to syntactic or grammatical categories such as noun, verb, adjectives and prepositions.

Word categories are systematically related by morphological processes such as the formation of plural form from the singular form.

Parts of Speech

Nouns, verbs, adjectives Determiners Adverbs She ran very quickly; She often

travels to Vegas; She started off impressively. Preposition She looked up the tree Particles She looked up the number Conjunctions, complementizer Funny but

stupid She is afraid that ….

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Syntax or Phrase Structure: A simple context-free grammar S --> NP VP NP --> DT NNS | DT NN | NP PP VP --> VP PP | VBD | VBD NP P --> IN NP

DT --> the NNS --> children | students | mountains VBD --> slept | ate | saw IN --> in | of NN --> cakeThe Grammar

The Lexicon

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Syntax or Phrase Structure: A Parse Tree

S NP VP

AT NNS VBD NP The children ate AT NN

the cake

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Local and Non-Local Dependencies Dependencies may be local e.g., DT NNS A non-local dependency is an instance in which

two words can be syntactically dependent even though they occur far apart in a sentence (e.g., subject-verb agreement; wh-extraction).

Non-local phenomena are a challenge for certain statistical NLP approaches (e.g., n-grams) that model local dependencies.

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Semantic Roles

Most commonly, noun phrases are arguments of verbs. These arguments have semantic roles: the agent of an action, the patient and other roles such as the instrument or the goal.

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Subcategorization Different verbs can relate different numbers of

entities: transitive versus intransitive verbs. Verbs are classified according to the type of

complements they permit. This called subcategorization.

FrameNet combines semantic roles and subcategorization. Let’s look up “put.v”

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Attachment Ambiguity and Garden-Path Sentences Attachment ambiguities occur with phrases

that could have been generated by two different nodes in the parse tree. E.g.: The children ate the cake with a spoon.

Garden-Path sentences are sentences that lead you along a path that suddenly turns out not to work. E.g.: The horse raced past the barn fell.

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Semantics Semantics is the study of the meaning of words,

constructions, and utterances. Semantics can be divided into two parts: lexical

semantics and combination semantics. Lexical semantics: hypernymy, hyponymy, antonymy,

meronymy, holonymy, synonymy, homonymy, polysemy (no need to memorize!).

Compositionality: the meaning of the whole is built up from the meanings of its parts different from its parts. (More on the next slide…)

Semantics:Idea of Strict Compositionality The overall meaning of a phrase or sentence

derives from the meanings of the constituent parts and the particular grammatical ways in which the parts are put together.

Let’s consider examples using the context free grammar we saw earlier …

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Syntax or Phrase Structure: A simple context-free grammar S --> NP VP NP --> DT NNS | DT NN | NP PP VP --> VP PP | VBD | VBD NP P --> IN NP

DT --> the NNS --> children | students | mountains VBD --> slept | ate | saw IN --> in | of NN --> cakeThe Grammar

The Lexicon

While the constituent parts of a sentence and its grammatical structure are important for determining its meaning, strict compositionality often breaks down

Idioms are one area of language where meanings are not compositional; “to be at a crossroads” means “facing a decision or choice”

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Pragmatics

Pragmatics is the area of studies that goes beyond the study of the meaning of a sentence and tries to explain what the speaker really is expressing.

Understand the scope of quantifiers, speech acts, discourse analysis, anaphoric relations.