Full Idea
The mind makes the particular ideas, received from particular objects, to become general,..by considering them as they are in the mind such appearances, separate from all other circumstances of real existence, as time or place. This is called ABSTRACTION.
Gist of Idea
The mind creates abstractions by generalising about appearances of objects, ignoring time or place
Source
John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 2.09.09)
Book Reference
Locke,John: 'Essay Concerning Human Understanding', ed/tr. Nidditch,P.H. [OUP 1979], p.159
A Reaction
What is distinctive here is that abstraction works on 'appearances' within the mind (which might be labelled 'sense-data'), rather than on the actual properties of the objects. Presumably abstraction can work on inferred unobservable properties?