Full Idea
Truth and falsehood belong, in propriety of speech, only to propositions; yet ideas are oftentimes termed 'true' or 'false ...though I think there is still some secret or tacit proposition.
Gist of Idea
It is propositions which are true or false, though it is sometimes said of ideas
Source
John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 2.32.01)
Book Reference
Locke,John: 'Essay Concerning Human Understanding', ed/tr. Nidditch,P.H. [OUP 1979], p.384
A Reaction
It is not quite clear, I think, what Locke means by 'proposition'. If it means sentences, then there are lots of problem cases like 'I am ill' (who is speaking?). I demand a theory of truth that allows animals to think truths. See Idea 12523.
Related Idea
Idea 12523 If they refer to real substances, 'man' is a true idea and 'centaur' a false one [Locke]