Full Idea
Our ideas of substance being supposed copies, and referred to archetypes within us, must still be taken from something that does or has existed; they must not consist of ideas put together at the pleasure of our thoughts.
Gist of Idea
Our ideas of substance are based on mental archetypes, but these come from the world
Source
John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 4.04.12)
Book Reference
Locke,John: 'Essay Concerning Human Understanding', ed/tr. Nidditch,P.H. [OUP 1979], p.568
A Reaction
This is a begrudging concession from Locke, who has been rather sarcastic about our supposed knowledge of substance. His is a realist about the physical world, and rightly says that our ideas are shaped by externals. We just don't have the evidence.