This paper puts together an ancientand a recent approach to classificatory language, thought, and ontology.It includes on the one hand an interpretation of Aristotle's ten categories,with remarks on his first category, called (or translated as) substancein the Categories or What a thing is in the Topics. On the other hand is the ideaof domain-specific cognitive abilities urged in contemporary developmentalpsychology. Each family of ideas can be used to understand the other. Neitherthe metaphysical nor the psychological approach is intrinsically morefundamental; they (...) complement each other. The paper incidentally clarifies distinct uses of the word category in different disciplines, and also attempts to make explicit several notions of domain. It also examines Aristotle's most exotic and least discussed categories, being-in-a-position (e.g., sitting) and having-(on) (e.g., armour). Finally the paper suggests a tentative connectionbetween Fred Sommers' theory of types and Aristotle's first category. (shrink)