Chapter 5.1

Constituency
Relations

Explore the hierarchical structure of language, where words coalesce to form phrases and meaning emerges from structure.

Understanding Constituency

Sentences aren't just strings of words; they are hierarchical structures. Words group into phrases, and phrases nest within larger constituents.

  • The Head

    The central word determining the category. E.g., "Book" is the head of the Noun Phrase "The old book".

  • Phrasal Categories

    We have NP (Noun Phrase), VP (Verb Phrase), and PP (Prepositional Phrase).

Interactive Parse Tree

S
Sentence
NP
The cat
VP
chased the mouse

👆 Click a node (S, NP, VP) to explore its function.

Constituency Tests

How do linguists prove a group of words is a constituent? We use diagnostic tests. Hover over the cards to see them in action.

Substitution

Can the phrase be replaced by a single word (like a pronoun)?

"The quick fox jumps."
"He jumps."

Movement

Can the phrase move to a different position in the sentence?

"The cat in the hat sat."
"In the hat, the cat sat."

Coordination

Can it be linked with a similar phrase using 'and' or 'or'?

"John ate an apple."
"...ate an apple and a pear."

Bracketing

Can you visually isolate the constituent boundaries?

"Alice loves to read books"
"[Alice] [loves to [read books]]"

Parsing Approaches

The evolution from rule-based algorithms to deep learning.

Top-Down

Like building a family tree in reverse. Starts from the root (S) and expands using grammar rules until words are matched.

Global View Inefficient (Backtracking)

Bottom-Up

Like a jigsaw puzzle. Starts with individual words ("Shift") and glues them into constituents ("Reduce").

Data Driven Spurious Constituents

Chart Parsing

The smart "memoization" method. Stores intermediate results in a chart to avoid re-analyzing the same phrase.

Dynamic Programming

Real World Applications

News Analysis

Parsers extract "who did what to whom".
E.g., identifying that "Company A" is the acquirer and "Company B" is the target.

Social Media

Decodes informal text. Handles hashtags, slang, and emojis by analyzing the underlying clause structure hidden in the noise.

Machine Translation

Vital for reordering words. E.g., converting SVO (English) to SOV (Japanese) requires knowing where the constituents are.