Full Idea
Natural kinds are the kinds one should make use of in inductive inference (if that is explanation which leads to laws).
Gist of Idea
Natural kinds are those that we use in induction
Source
Alexander Bird (Philosophy of Science [1998], Ch.3)
Book Reference
Bird,Alexander: 'Philosophy of Science' [UCL Press 2000], p.119
A Reaction
The problem with this is that it is epistemological rather than ontological. In induction we use superficial resemblences that are immediately obvious, whereas the nature of kinds can be buried deep in the chemistry or physics.