Full Idea
We can never be sure that we know all the powers that are in any one body, till we have tried what changes it is fitted to give to or receive from other substances, in their several ways of application.
Gist of Idea
We can only know a thing's powers when we have combined it with many things
Source
John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 2.31.08)
Book Reference
Locke,John: 'Essay Concerning Human Understanding', ed/tr. Nidditch,P.H. [OUP 1979], p.381
A Reaction
This must include the possibility that some combinations are never tried, in nature or by us, and so the powers remain permananently hidden. Maybe the combination of copper and element 147 produces chaffinches.