Full Idea
In substances the most frequent [ideas] are of powers; v.g. 'a man is white' signifies that the thing that has the essence of a man has also in it the essence of whiteness, which is nothing but the power to produce the idea of whiteness in one with eyes.
Gist of Idea
The essence of whiteness in a man is nothing but the power to produce the idea of whiteness
Source
John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 3.08.01)
Book Reference
Locke,John: 'Essay Concerning Human Understanding', ed/tr. Nidditch,P.H. [OUP 1979], p.474
A Reaction
Alexander cites this to support his claim that the powers are the same as the textures, but the quotation seems neutral about what actually constitutes the powers, and Idea 15971, seems to separate powers from textures.
Related Ideas
Idea 15971 Secondary qualities are powers of complex primary qualities to produce sensations in us [Locke]
Idea 15973 In my view Locke's 'textures' are groups of corpuscles which are powers (rather than 'having' powers) [Locke, by Alexander,P]
Idea 15976 What is the texture - the real essence - which makes substances behave in distinct ways? [Locke]