form class

linguistics

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June 26, 2026

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In linguistics, a form class refers to a group of words or linguistic units that share common grammatical features and can occupy the same position within a sentence's structure. These classes are similar to traditional parts of speech but are defined by their syntactic behavior and substitutability.12

For example, "personal substantive expressions" like "John" or "Boy" form a class because they can be used in similar ways, such as calling for attention. Similarly, "infinitive expressions" like "run" or "jump" can function as commands. A single word can belong to multiple form classes depending on its usage. The concept of form classes is central to understanding syntax and how words combine to create meaning.2

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linguistics
Syntax
…syntax were the notions of form classes and constituent structure. (These notions were also relevant, though less central, in the theory of morphology.) Bloomfield defined form classes, rather imprecisely, in terms of some common “recognizable phonetic or grammatical feature” shared by all the members. He gave as examples the form…
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…syntax were the notions of form classes and constituent structure. (These notions were also relevant, though less central, in the theory of morphology.) Bloomfield defined form classes, rather imprecisely, in terms of some common “recognizable phonetic or grammatical feature” shared by all the members. He gave as examples the form…
Read More