Full Idea
In this whole business of genera and species, the genus, or more comprehensive, but a partial conception of what is in the species, and the species but a partial idea of what is to be found in each individual.
Gist of Idea
Genus is a partial conception of species, and species a partial idea of individuals
Source
John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 3.06.32)
Book Reference
Locke,John: 'Essay Concerning Human Understanding', ed/tr. Nidditch,P.H. [OUP 1979], p.460
A Reaction
This is my feeling on the subject, that any definition that stops short of the individual, whence all categorisation flows, is inadequate.