 By contrast, the ideas that we use to make up our nominal essences come to us from experience. Locke claims that the mind is active in making our ideas of sorts and that there are so many properties to choose among that it is possible for different people to make quite different ideas of the essence of a certain substance. This has given some commentators the impression that the making of sorts is utterly arbitrary and conventional for Locke and that there is no basis for criticizing a particular nominal essence. Sometimes Locke says things that might suggest this. But this impression should be resisted. Peter Anstey has characterized Locke’s conventionalism about classificatory terms as both constrained and convergent (Anstey 2011: 209, 212). Locke claims that while the making of nominal essences is the work of the understanding, that work is constrained both by usage (where words stand for ideas that are already in use) and by the fact that substance words are supposed to copy the properties of the substances they refer to. Locke says that our ideas of kinds of substances have as their archetype the complex of properties that produce the appearances we use to make our nominal essences and which cause the unity of the complex of ideas that appear to us regularly conjoined. The very notion of an archetype implies constraints on what properties (and hence what ideas) can go together. If there were no such constraints there could be no archetype. (For further discussion of the nominal-real essence distinction see the entry  Locke on Real Essences).