Syntactic Rules

Syntactic rule states what words can form a syntactic category and in what order.

NP(the cat) -> Det(the) N(cat)

Lexical Entity

Lexical Entity

A rule that spells out individual words in a category.

N -> cat, mouse, dog, person

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Rule Types

• Head rules (XP -> ... X ...): Expand a phrase into a head plus complements/specifiers (e.g., VP -> V NP, PP -> P NP).
• Adjunction rules (X -> ... X ...): Expand a category into itself plus optional adjuncts (e.g., VP -> VP Adv, N -> Adj N).
• Exocentric rules: Expand a category into other categories of different types (e.g., TP -> NP T' or S -> NP VP).# Syntactic Rule Examples
• Recursive rule: a syntactic rule can be recursive. (e.g., N -> Adj N)

Syntactic Rule Examples

• S: S -> NP VP
• VP: VP -> V, VP -> TV NP, VP -> DTV NP NP, VP -> SV S, VP -> VP Adv, VP -> VP PP
• NP: NP -> Det N, NP -> PropN
• N: N -> Adj N, N -> N PP
• PP: PP -> P NP

General Phrase Structure Principles

• Head (X): Core element that projects into a phrase of the same type (XP).
• Specifiers: Provide additional information about the head. (e.g., Det in NP)
• Complements: Required by heads to complete the phrase.
• Modifiers: Optional elements. Can be freely reordered relative to each other.

Sentence as Tense Phrase

A sentence combines a subject and a predicate incorporating tense via a Tense Phrase (TP).

• Head (T): Tense ([+past] or [-past]) or Modals (can, will, must). Modals take the place of tense under T, making the following verb non-tensed.
• Specifier: Subject NP.
• Complement: Predicate VP.

Auxiliaries (AuxP)

Function as helping verbs between TP and VP.

Start with a sentence "He would have left".
TP
├─ NP
│  └─ N: He
├─ T: would
└─ AuxP
   ├─ Aux: have
   └─ VP
      └─ V: left

• Progressive auxiliary: continuation of an event. e.g., is V-ing, was V-ing
• Perfective auxiliary: completion of an event. e.g., had V-ed, have V-ed
• Passive auxiliary: focus on the object of the sentence. e.g., is V-ed, are V-ed

Generation

Generation (Syntax)

Start with S and randomly choose which rules to follow until you have generated a sentence.

Start with "S"
S
├─ NP
│  ├─ Det: that
│  └─ N: person
└─ VP
   ├─ VP
   │  └─ V: slept
   └─ Adv: badly

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Parsing

Parsing (Syntax)

Start with a sentence and figure out how it could have been generated by the rules.

Start with a sentence "Sally thought the dog chased the furry cat".
S
├─ NP
│  └─ PropN: Sally
└─ VP
   ├─ SV: thought
   └─ S
      ├─ NP
      │  ├─ Det: the
      │  └─ N: dog
      └─ VP
         ├─ TV: chased
         └─ NP
            ├─ Det: the
            └─ N
               ├─ Adj: furry
               └─ N: cat

Process of Parsing a Sentence

1. Label the categories for all the individual words.
2. Find a sequence of categories that matches the right-hand side of a rule.
3. Draw a tree with the left-hand side of the rule on top.
4. Repeat until you have a single tree that covers all the words in the sentence.

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