ABSTRACT
Prototypical examples of natural kinds are chemical elements and types of fundamental physical particles. Natural kinds are objective – the differences between them are fixed by the structure of the world, rather than being imposed by human minds – and they are theoretically important. Whether the kinds investigated by a discipline are natural kinds is a question of key importance to New Essentialists and other causal realists. Causal realists claim that the world is full of powerful particulars. These particulars fall into natural kinds, and each particular behaves in ways characteristic of its kind. Thus, where there are natural kinds there will also be real causal powers, and, as members of a natural kind behave predictably, there will also be natural laws. This in turn implies that where there are natural kinds it will be possible to make sound inductive inferences. For example, as oxygen is a natural kind, we are justified in concluding that the flame will burn brightly in this test-tube of oxygen, as it has in all the other testtubes of oxygen. Where there are kinds we can also explain the behaviour of individuals by reference to the kind to which it belongs (so, for example, we can explain that the key is attracted to the magnet because it is made of iron). In short, whether a domain consists of natural kinds matters, because with natural kinds come natural laws, and the possibility of explanations and sound inductive inferences.1
