This document discusses syntax and sentence structure. It defines syntax as the rules of sentence formation and the component of grammar that represents a speaker's knowledge of phrase and sentence structure. It discusses constituents, phrase structure rules, syntactic categories, and phrase structure trees. Phrase structure trees are used to represent the hierarchical structure of sentences and show constituent structures and syntactic categories. The document notes that language has an infinite quality, as sentences can always be lengthened through the addition of modifiers. It provides examples of phrase structure trees and tests to identify verbs phrases and noun phrases.