The nature of parts of speech

Abstract Parts of speech have both semantic and structural aspects. The two sets of features are essentially incommensurate, since the semantic features derive from the functions of language in communication and cognition, while the structural features are essentially based in the combinatorial potential of signs in a text. Consequently, the two sets of features are largely independent of each other.Their combination in a language yields sets of parts of speech whose systematicity is largely language-internal. To the extent that there is a functional motivation for parts of speech, three restrictions must be made: 1) It is not, in the first place, a cognitive, but rather a communicative motivation. 2) The functional motivation of word classes is not direct, but mediated by semantic and syntactic categories of higher order. 3) Only the primary word classes (verb and noun) are motivated in this way. The secondary classes (adjectives, adverbs etc.) and the minor word classes (pronouns, subordinators etc.) increasingly have a systeminternal structural rather than a universal functional motivation. Given these heterogeneous functions and constraints, there is no uniform nature to all parts of speech.