Full Idea
Essential kinds can be very specific, and arguably too specific for the purposes of ontological categories.
Gist of Idea
Essential kinds may be too specific to provide ontological categories
Source
Jan Westerhoff (Ontological Categories [2005], §27)
Book Reference
Westerhoff,Jan: 'Ontological Categories' [OUP 2005], p.64
A Reaction
Interesting. There doesn't seem to be any precise guideline as to how specific an essential kind might be. In scientific essentialism, each of the isotopes of tin has a distinct essence, but why should they not be categories