Abstract: Central to Mary Shepherd's philosophical system is her theory of kind membership. However, there is a problem with this theory that has gone largely unnoticed. My first goal is to articulate this problem, and my second goal is to solve it. The problem is that Shepherd apparently thinks that there are non-basic natural kinds with members while also being committed to theses which imply all such kinds must be empty. The solution is to clarify her account of natural kinds via a distinction between genuine kinds with real definitions comprised of causal powers and merely nominal kinds with stipulative definitions comprised of sensible effects. In other words, I argue that Shepherd's apparent talk of non-basic kinds is really tracking what Shepherd (following Locke) calls nominal essences. Since non-basic kinds are merely nominal, there is no contradiction between her metaphysical theory of kind membership and her theory of non-basic kinds.

I then consider how this theory of kind membership interacts with one of Shepherd's main philosophical projects: justifying ordinary cases of induction contra Hume. Shepherd thinks that ordinary induction concerns nominal kinds, like 'fire' and 'candle.' Furthermore, Shepherd thinks we are justified in making inductions concerning these kinds. But, since nominal kinds are defined by us, is Shepherd simply attempting to define her way out of Hume's problem? And, if she is not, how does she justify her theory of induction?

I argue that Shepherd's theory of cause and effect provides her with a solution to Hume's riddle of induction. Because, for Shepherd, there is nothing in an effect that is not in a cause, and causation is understood in terms of a union of causes into an effect, the essences of unions correspond with the essences of their more basic causal components. So, tracing this down to the fundamental level, the essences of all causal unions will correspond to the essences of the most fundamental objects, which Shepherd takes to be members of basic, elemental kinds, and thus our nominal kinds track consistent and necessary features of real kinds. This causal theory, I argue, combined with a denial of a Humean recombination principle, provides Shepherd with a non-question-begging response to Hume's problem of induction even for non-basic, nominal kinds.