sortal predicate roughly, a predicate whose application to an object says what kind of object it is and implies conditions for objects of that kind to be identical. Person, green apple, regular hexagon, and pile of coal would generally be regarded as sortal predicates, whereas tall, green thing, and coal would generally be regarded as non-sortal predicates. An explicit and precise definition of the distinction is hard to come by. Sortal predicates are sometimes said to be distinguished by the fact that they provide a criterion of counting or that they do not apply to the parts of the objects to which they apply, but there are difficulties with each of these characterizations. The notion figures in recent philosophical discussions on various topics. Robert Ackermann and others have suggested that any scientific law confirmable by observation might require the use of sortal predicates. Thus ‘all non-black things are non-ravens’, while logically equivalent to the putative scientific law ‘all ravens are black’, is not itself confirmable by observation because ‘non-black’ is not a sortal predicate. David Wiggins and others have discussed the idea that all identity claims are sortal-relative in the sense that an appropriate response to the claim a % b is always ‘the same what as b?’ John Wallace has argued that there would be advantages in relativizing the quantifiers of predicate logic to sortals. ‘All humans are mortal’ would be rendered Ex[m]Dx, rather than Ex(MxPDx). Crispin Wright has suggested that the view that natural number is a sortal concept is central to Frege’s (or any other) number-theoretic platonism. The word ‘sortal’ as a technical term in philosophy apparently first occurs in Locke’s Essay Concerning Human Understanding. Locke argues that the so-called essence of a genus or sort (unlike the real essence of a thing) is merely the abstract idea that the general or sortal name stands for. But ‘sortal’ has only one occurrence in Locke’s Essay. Its currency in contemporary philosophical idiom probably should be credited to P. F. Strawson’s Individuals. The general idea may be traced at least to the notion of second substance in Aristotle’s Categories.
See also ARISTOTLE , CAUSAL LAW, ESSEN- TIALISM , PHILOSOPHY OF LANGUAG. S.T.K.