A definition of an analytic, a contradictory and a generic sentence, based on the notion of presupposition, is proposed. A sentence is analytic iff it presupposes itself, is contradictory iff it presupposes its own negation, and is generic iff its presuppositions are analytic. A difference is made between an analytic and a necessarily true sentence, and between a contradictory and a necessarily false sentence. There are sentences which are both analytic and contradictory- they are never true and never false. Analytic (...) sentences can have non-trivial consequences, but they are not asserted but presupposed. This fact permits to avoid some classical difficulties with the definition of analytic sentences. A paralleHsm between analytic and generic sentences is indicated. (shrink)