By Hume's fork, a statement's "meaning" either is analytic or is synthetic, the statement's "truth"—its agreement with the real world—either is necessary or is contingent, and the statement's purported "knowledge" either is or is . An analytic statement is true via its terms' meanings alone, hence true by definition, like "Bachelors are unmarried", whereas a synthetic statement, concerning external states of affairs, may be false, like "Bachelors age badly". By mere logical validity, the necessary is true in all possible worlds, whereas the contingent hinges on the world's state, a metaphysical basis. And the "a priori" is knowable without, whereas the "a posteriori" is knowable only upon, experience in the area of interest.