Syntactic Categories and Constituents
Syntax is all about how words combine into phrases and sentences. Syntactic categories tell you what kind of word you're dealing with, and constituency tells you how those words group together. These two concepts are the foundation for everything else in syntax.
Syntactic Categories
Major syntactic categories
Every word in a sentence belongs to a syntactic category (also called a part of speech or word class). The major categories carry the core meaning of a sentence:
- Nouns (N) represent people (teacher), places (Paris), things (book), or ideas (freedom). They function as subjects, objects, or complements in sentences.
- Verbs (V) express actions (run), states (exist), or occurrences (happen). The verb serves as the main predicate of the sentence.
- Adjectives (Adj) modify nouns or pronouns, describing qualities (red) or attributes (intelligent).
- Adverbs (Adv) modify verbs, adjectives, or other adverbs. They provide information about manner (quickly), time (yesterday), place (here), or degree (very).
- Prepositions (P) show relationships between words, indicating spatial (under), temporal (before), or logical (despite) connections.
Lexical vs. functional categories
Not all categories work the same way. Linguists draw a key distinction between lexical and functional categories.
Lexical categories are the open-class words: nouns, verbs, adjectives, and adverbs. They carry the primary meaning in a sentence, and new words are regularly added to these classes. Think of how selfie or google (as a verb) entered the language.
Functional categories are the closed-class words: determiners (the, a), auxiliaries (will, have, be), conjunctions (and, but), and complementizers (that, whether). These words provide grammatical structure rather than content meaning. They're a small, fixed set that rarely accepts new members.
Both types work together to build well-formed sentences:
- Lexical categories form the core meaning of phrases: big dog, run fast
- Functional categories connect and shape those phrases: the big dog, will run fast
- Functional categories often control how lexical items are distributed. Compare a book (singular, with the indefinite article) vs. books (plural, no article needed).
Constituents
The concept of constituency
A constituent is a group of words that functions as a single unit within a larger structure. In the sentence The big dog chased the cat, the words the big dog form a constituent because they work together as the subject.
Sentences have a hierarchical structure, meaning constituents nest inside other constituents. The big dog is a noun phrase (NP), and within it, big modifies dog. You can represent this nesting like this: [The [big] dog].
Words group into phrases, and phrases combine to form clauses and sentences. The main phrase types you'll encounter are noun phrases (NP), verb phrases (VP), prepositional phrases (PP), and adjective phrases (AdjP).
Constituency tests
How do you prove that a group of words is actually a constituent? You use constituency tests. These are the three most common:
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Substitution — Replace the group of words with a single word (often a pronoun). If the sentence still works, the group is a constituent.
- The man in the hat left → He left (so the man in the hat is a constituent)
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Movement — Move the group of words to a different position in the sentence. Constituents can move as a unit; non-constituents can't.
- The man stood in the hat → In the hat, the man stood (so in the hat is a constituent)
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Coordination — Join two groups with a conjunction like and or or. Only constituents of the same type can be coordinated.
- The man in the hat and the woman in the coat left (both are NPs, confirming they're constituents)
No single test is foolproof on its own. Use multiple tests together to build a stronger case.
Analyzing constituent structure
Once you've identified constituents, you can map out the full structure of a sentence. Two common tools for this:
- Tree diagrams visually represent the hierarchical structure of a sentence. Each branching point shows how a constituent breaks into smaller parts. You'll work with these extensively in syntax.
- Immediate constituent analysis breaks a sentence into progressively smaller parts, identifying the head (the core word of a phrase, like the noun in a noun phrase) and its complements (the elements that complete its meaning) at each level.
For example, in The cat sat on the mat, you'd first split into the subject NP (the cat) and the VP (sat on the mat). Then you'd break the VP into the verb (sat) and the PP (on the mat), and so on, until every word is accounted for.