Since Greenberg’s groundbreaking publication on universals of grammar, typologists have used semantic categories to investigate (constraints on) morphological and syntactic variation in the world’s languages and this tradition has been continued in the WALS project. It is argued here that the employment of semantic categories has some serious drawbacks, however, suggesting that semantic categories, just like formal categories, cannot be equated across languages in morphosyntactic typology. Whereas formal categories are too narrow in that they do not cover all structural variants attested across languages, semantic categories can be too wide, including too many structural variants. Furthermore, it appears that in some major typological studies semantic categories have been confused with formal categories. A possible solution is pointed out: typologists first need to make sure that the forms or constructions under investigation do the same job in the various languages (functional sameness); subsequently this functional selection can be narrowed down on the basis of formal or semantic criteria to construct a set of elements that is similar enough to allow for crosslinguistic comparison (formal and semantic similarity).
