Full Idea
The natural thought is to think that real kinds are given only by classification on the basis of essential properties: properties that make an object the kind of thing that it is.
Gist of Idea
Kinds are fixed by the essential properties of things - the properties that make it that kind of thing
Source
Antony Eagle (Locke on Essences and Kinds [2005], II)
A Reaction
Circularity alert! Circularity alert! Essence gives a thing its kind - and hence we can see what the kind is? Test for a trivial property! Eagle is not unaware of these issues. Does he mean 'necessary' rather than 'essential'?