Full Idea
Even if we guessed that the two words denoted the two truth-values, we should not know which stood for the value 'true' and which for the value 'false' until we knew how the sentences were in practice used.
Gist of Idea
We could only guess the meanings of 'true' and 'false' when sentences were used
Source
Michael Dummett (Thought and Reality [1997], 4)
Book Reference
Dummett,Michael: 'Thought and Reality (Gifford Lectures)' [OUP 2006], p.52
A Reaction
These types of problem are always based on the idea that some one item must have logical priority in the process, but there is a lot of room for benign circularity in the development of mental and linguistic functions.