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In a traditional subject-predicate analysis, a predicate is the portion of a clause that says something about its subject. It can include a verb together with other material, rather than being identical to a single verb form.^[ref]

For The sample changed color, the subject is the sample and the predicate is changed color. In The sample is red, is red expresses the predication, although the central property is contributed by the adjective red. The examples show why “predicate” and “action word” are not interchangeable classifications.

An explicit model can distinguish the grammatical expression from its interpretation. A formal semantics might represent the property red by a set and ask whether the sample belongs to it, while the syntax describes how is red combines with the subject. The linguistic unit and the mathematical representation are related analytical choices.