Full Idea
Anyone who observes their different qualities can hardly doubt that many of the individuals, called by the same name, are, in their internal constitution, as different from one another as several of those which are ranked under different specific names.
Gist of Idea
Many individuals grouped under one name vary more than some things that have different names
Source
John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 3.10.20)
Book Reference
Locke,John: 'Essay Concerning Human Understanding', ed/tr. Nidditch,P.H. [OUP 1979], p.501
A Reaction
I take this to agree with Aristotle, and disagree with the medieval scholastic view that essences pertain to species. Locke and I think that the so-called essences of natural kinds and sortal classes are just loose inductive generalisations.
Related Idea
Idea 15993 If we observe total regularity, there must be some unknown law and relationships controlling it [Locke]