Full Idea
It is plain that general and universal belong not to the real existence of things; but are the inventions and creatures of the understanding, made by it for its own use, and concern only signs, whether words or ideas.
Gist of Idea
General and universal are not real entities, but useful inventions of the mind, concerning words or ideas
Source
John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 3.03.11)
Book Reference
Locke,John: 'Essay Concerning Human Understanding', ed/tr. Nidditch,P.H. [OUP 1979], p.414
A Reaction
Frege and Geach viciously attacked this view, and it seems to be discredited, but I think it is time for a revival, given that the alternative view seems to lead to platonism. I take the first step in mental abstractionism to be pre-verbal.