A proposition can be true or false only by being an image of reality.

When reality and the proposition are compared, one must not overlook that fact that a proposition makes sense independently of the facts. That error would lead one to suppose that true and false are relations between signs and what they signify, and have equal status. One could declare, for example, that (p) signifies in the true way what (~p) signifies in the false way, etc.

Could we not communicate using false propositions just as we have up to now with true ones, as long as one knows that they are meant to be false? No!

A proposition is true if things really are as it says they are. Now let us mean (~p) if we say (p) and let things actually be as we mean them. Then, because we construe reality in the new way, (p) is true and not false.

But that the signs 'p' and '~p' could possibly say the same thing is important. For it shows that nothing in reality corresponds to the sign '~'. The occurrence of negation in a proposition is not enough to characterize its sense (~~p = p). The propositions 'p' and '~p' may have opposite sense, but one and the same reality corresponds to them.