 While it is widely believed that some necessary truths are capable of justification and can be known only empirically (e.g., “Water is H2O”), some contingent truths also seem justifiable, and knowable, a priori. Saul Kripke proposed that “the standard meter stick, S, in Paris is a meter long at \(t_0\)” is such an example (Kripke 1972: 274–275). “The length of S in the actual world at \(t_0\)” rigidly designates that length, that is, it refers to length L in every possible world. The reference of “one meter” is given by that reference-fixing description, so “one meter” rigidly designates L. However, “the length of S at \(t_0\)” does not rigidly designate any particular length since at \(t_0\) in other possible worlds S will be longer or shorter than L. So the proposition that “S is a meter long at \(t_0\)” is contingent because in other possible worlds that very same stick will be shorter or longer than it was in the actual world at that time. Still, we can know a priori, that is, independent of any empirical evidence, that “S is a meter long at \(t_0\)” is true in the actual world given that we know how the reference of “one meter” is fixed by a description that refers to the length of S in the actual world. If empirical evidence plays any role, it is only insofar as we need it to know that there really is a stick, S, that was designated as the meter at some particular time and place. 