Full Idea
Essence, in the ordinary use of the word, relates to sorts; ..take but away the abstract ideas by which we sort individuals, and rank them under common names, and then the thought of anything essential to any of them instantly vanishes.
Gist of Idea
Essences relate to sorting words; if you replace those with names, essences vanish
Source
John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 3.06.04)
Book Reference
Locke,John: 'Essay Concerning Human Understanding', ed/tr. Nidditch,P.H. [OUP 1979], p.440
A Reaction
The claim seems to be that if you refer to 'the dog', you instantly see its doggy essence, but if you refer to 'Fido' you see no such thing. But he is confusing the name with the idea. 'Fido' reveals no essence, but my idea of my beloved dog does.