Constituent (linguistics)

In syntactic analysis, a constituent is a word or a group of words that functions as a single unit within a hierarchical structure.

Phrases (noun phrases, verbal phrases, etc.) are usually constituents of a clause, but clauses may also be embedded into a bigger structure. For example, in the clause "I didn't hear what you said," the subordinate clause "what you said" is embedded into the main clause and is syntactically its object; this can be demonstrated by substituting the pronoun "it" for the subordinate clause "what you said"; the result of this substitution is the clause "I didn't hear it."

Constituency tests

Various constituency tests exist. Some syntacticians arrange such tests on a scale of reliability, with less-reliable tests treated as useful to confirm constituency though not sufficient on their own by Eric Bakovic of University of California, San Diego.

Failing to pass a test, however, does not always mean that the unit is not a constituent. It is best to apply as many tests as possible to a given unit in order to prove or to rule out its constituency.

Substitution (replacement)

Using "it" instead of the whole clause "what you said" is called substitution, or replacement. This is one of the tests used to determine the internal structure of a sentence, i.e. to determine its constituents. Substitution normally involves using pronouns like...
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