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Full Idea
The original or 'primary' qualities of body produce simple ideas in us, viz. solidity, extension, figure, motion or rest, and number.
Gist of Idea
Primary qualities produce simple ideas, such as solidity, extension, motion and number
Source
John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 2.08.09)
Book Ref
Locke,John: 'Essay Concerning Human Understanding', ed/tr. Nidditch,P.H. [OUP 1979], p.135
A Reaction
The tricky word here is 'simple', which clearly won't be enough on its own to distinguish primary from secondary qualities. Notice that there is a germ of an empirical theory of arithmetic in the word 'number'.