A number of people question why I used the phrase “natural kinds” to describe what I’m talking about when I talk about categorization. My brief explanation runs something like this:
In giving an account of things, sometimes it’s possible to divide things up in pretty much any way and have it work out. Other times, we inherit or impose category schemes that make it hard or impossible to give a successful account. Still other times, our taxonomy especially allows for successful enquiry— that is, it works but proceeding with a substantially different taxonomy would not have. By natural kind I mean kinds that figure in the latter sort of taxonomy.
In the former sorts of cases, the kinds in our taxonomy are merely conventional. In the latter sort, there are not merely conventional. So my natural kinds are the ones which are not merely conventional, and the phrase “natural kinds” seemed apt to mark that contrast. Jim Woodward once suggested unhelpfully that I might instead call them unconventional kinds.
Several people have suggested that I might instead adopt Nelson Goodman’s phrase and call them relevant kinds. I resist, because it has the wrong connotation.
I think Goodman means something different than I do. Here’s his justification for not saying “natural kinds”:
[W]orlds differ in the relevant kinds they comprise. I say “relevant” rather than “natural” for two reasons: first, “natural” is an inapt term to cover not only biological species but such artificial kinds as musical works, psychological experiments, and types of machinery; and second, “natural” suggests some absolute categorical and psychological priority, while the kinds in question are rather habitual or traditional or devised for a new purpose.1
The first reason resonates with me a bit. Some people hear “natural” and think that the contrast must be with artificial, whereas for me the contrast is with merely conventional. Nevertheless, I want to insist that music, psychology, and machinery are not somehow above or outside of nature. Even if types of machinery won’t be natural kinds for the botanist, they might well be for the anthropologist or the engineer.
The second reason shows (I think) that Goodman’s usage is not strong enough for what I have in mind. It’s true that my natural kinds are not absolute categories, but it’s not true that any merely habitual or traditional category gets to count as natural. Contrariwise, I take it that for Goodman traditional categories all get to count as relevant kinds— relevant at least until the tradition changes.