Categories

Categories are hard to describe, and even harder to define. This is in part a consequence of their complicated history, and in part because category theory must grapple with vexed questions concerning the relation between linguistic or conceptual categories on the one hand, and objective reality on the other. In the mid-fourth century bc,Aristotle initiates discussion of categories as a central enterprise of philosophy. In the Categories he presents an ‘ontological’ scheme which classifies all being into ten ultimate types, but in the Topics introduces the categories as different kinds of predication, that is, of items such as ‘goodness’ or ‘length of a tennis court’ or ‘red’, which can be ‘predicated of’ subjects. He nowhere attempts either to justify what he includes in his list of categories or to establish its completeness, and relies throughout on the unargued conviction that language faithfully represents the most basic features of reality. In the twentieth century, a test for category membership was recommended by Ryle, that of absurdity: concepts or expressions differ in logical type when their combination produces sentences which are palpable nonsense.Kant, working in the eighteenth century, derives his categories from a consideration of aspects of judgments, hoping in this manner to ensure that his scheme will consist exclusively of a priori concepts which might constitute an objective world. The Sinologist Graham argues that the categories familiar in the West mirror Indo-European linguistic structure, and that an experimental Chinese scheme exhibits suggestively different properties, but his relativism is highly contentious.