Full Idea
Let us suppose the mind to be, as we say, white paper, void of all characters, without any ideas. How comes it to be furnished? Whence has it all the materials of reason and knowledge? To this I answer, in one word, from Experience.
Gist of Idea
All the ideas written on the white paper of the mind can only come from one place - experience
Source
John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 2.01.02)
Book Reference
Locke,John: 'Essay Concerning Human Understanding', ed/tr. Nidditch,P.H. [OUP 1979], p.104
A Reaction
In the face of Kant's wonderfully rich account of the mind, this simple empiricism seems to be horribly naïve, but it could be defended by saying that all the other paraphernalia of the mind (associations, categories etc) are not in any way ideas.