On Natural Properties in Metaphysics

Abstract

Michael Dummett has characterized the primary claim of realism as being that sentences are objectively true. But even if he is right, so that it is at the level of sentences that realism's essence is revealed, realists have traditionally also had theses to advance about the components out of which sentences are built. One of these, of course, is the claim that at least some singular terms stand for entities which exist objectively and independently of mind. Another, the topic of this paper, is that at least some predicates stand for natural proper-ties; that is, that they record objective cleavages in nature, schisms in things independent of human psychology or convention, marking entirely mind-independent similarities between things. Historically, the importance in realist metaphysics of doctrines of natural properties will be obvious: in Plato's distinction between predicates like and pious which mark the Forms, and those like dirt and hair which do not; in Aristotle's contrast between predicates like man which stand for substantial forms, and those like musician orstatue which correspond to mere accidental unities or to artifacts; and in the consequent doctrines of species, genera, and real essence which run through the scholastics to the modems. But with Kant and the passing of traditional realism, and more so with the linguistic turn and the passing of traditional metaphysics in its entirety, doctrines of natural properties went rather out of fashion, and in the analytic tradition of this century they find few defenders. True, Quinton (1957) and Quine (1969) dabble with the natural, but both end up with an account too tainted with psychology to count as a true doctrine of natural properties in the present sense. Which leaves just a few isolated figures, such as the trope theorist Donald C. Williams (1953), as the last friends natural properties have. Or did, until quite recently. For as the linguistic turn loses impetus, metaphysics has been reborn within the analytic tradition and realists have re-embraced doctrines of natural properties. Keith Campbell (1990) and David Armstrong (1978) are prime exemplars of the trend. But nowhere are natural properties put to more sophisticated use than in the metaphysical system of David Lewis. This paper examines the reasons Lewis gives for believing in natural properties, and charts and evaluates the way he deploys them. In so doing, my discussion perforce engages with the detail of Lewis's system, but I trust the morals drawn are more general; that clarifying the standing of natural properties within the most comprehensive contemporary system of realist metaphysics sheds light on their significance for any system with reasonable claims to be an alternative.