One of the activities of metaphysics is the elucidation of basic categories. Basic categories are the fundamental kinds of thing of which the world is made, or 'the basic divisions which our thought and talk about reality entail' (Carr 1987: 2). As such, basic categories form part of the foundations of the psychological construction of reality: ascertaining what the basic categories of this construction are yields the most general, overall organisation of the construction, the most general definition of clear research problems. This is not to say that psychologically basic categories necessarily match those to be found in any philosophical theory: they are not the products of ratiocination but have a psychological origin, which I shall attempt to elucidate in a later section. But in the absence of psychological theories about basic categories, philosophy is a useful starting-point for exploration of this problem.