To have a propositional attitude, a thinker must possess the concepts included in its content. Surprisingly, this rather trivial principle refl ects badly on many theories of concept possession because, in its light, they seem to require too much. To solve this problem, I point out an ambiguity in attributions of the form ' possesses the concept ofs'. There is an undemanding sense which is involved in the given principle, whereas the theoretical claims concern a stronger sense which can be brought out by formulations such as ' has an adequate conception ofs' or ' knows whats are'.
Kant distinguishes concept negation from copula negation. While the latter results in a negative judgement, i.e. a judgement denying a property of certain objects, the former gives rise to a negative concept, such as ‘immortal’. Since Kant’s remarks on concept negation are scattered and inconclusive, five interpretations are worked out and put to the test: logical negation, pseudo-negation, attribution of a zero degree, possibility-restricted negation and genus-restricted negation. Whereas the first four interpretations fail for a number of reasons, genus-restricted negation turns out to be tenable.