In what sense, and to what extent, do rules of inference determine the meaning of logical constants? Motivated by the principle of charity, a natural constraint on the interpretation of logical constants is to make the rules of inference come out sound. But, as Carnap observed, although this constraint does rule out some non-standard interpretations, it does not rule them all out. This is known as Carnap’s problem. I suggest that a charitable interpretation of the logical constants should, as far as possible, make the rules of inference both sound and complete, and I show how this idea can be brought to bear on a successful solution to Carnap’s problem in the case of classical propositional logic, as well as classical first-order logic. In fact, the solution generalizes to any logic whose rules of inference are sound and complete with respect to a bivalent semantics that is classical with respect to negation.