Linguistic categories play a key role in virtually every theory that has a bearing on human language. This paper presents a connectionist model of grammatical category formation and use, within the domain of the German nominal system. The model demonstrates (1) how categorical information can be created through cooccurrence learning; (2) how grammatical categorization and inflectional marking can be integrated in a single system; (3) how the use of cooccurrence information, semantic information and surface feature information can be usefully combined in a learning system; and (4) how a computational model can scale up toward simulating the full range of phenomena involved in an actual system of inflectional morphology. This is, to our knowledge, the first connectionist model to simultaneously address all these issues for a domain of language acquisition.