 Kripke (1980;1971) famously argues that because a rigid designator designates the same object in all possible worlds, an identity statement in which both designators are rigid must be necessarily true if it is true at all, even if the statement is not a priori. His classic example is the identity statement ‘Hesperus is identical with Phosphorus’, which is true, but which was discovered a posteriori to be true. (Let us understand a “statement” to be a sentence under an interpretation; and, following Kripke’s notation in 1971 and elsewhere, let us shorten ‘Hesperus is identical with Phosphorus’ to ‘Hesperus = Phosphorus’ even though Kripke does not do that in 1980.) ‘Hesperus’ is a name that was given to a heavenly body seen in the evening, and ‘Phosphorus’ is a name that was, unknown to the first users of the name, given to that same heavenly body seen in the morning. The heavenly body is Venus.