Abstract

A central aspect of science is the classification of natural phenomena. Not only is this to some extent an end in itself, an account of what kinds of things there are being an important part of the picture of the world that science aims to provide. but classification is also inextricably connected with the development of scientific theories. The change from phlogiston theory to atomic chemistry, for example, involved not just a different theory but an entirely new way of sorting the domain of chemistry into kinds. It is often supposed that a necessary condition for an adequate or correct scientific theory is that its generalizations be formulated in terms of natural kinds ‐ those kinds, roughly speaking, that really exist in nature. Thus oxygen, but not dephlogisticated air, may be said to mark a natural kind. Natural kinds are sometimes conceived precisely as being those kinds to which true scientific laws apply. In addition, natural kinds have generally been thought of as defined by the common possession of an essence, a property both necessary and sufficient for an entity to be a member of the kind, and from which the further important properties of the kind flow.