Quotation by Saul Kripke

Any necessary truth, whether a priori or a posteriori, could not have turned out otherwise. In the case of some necessary a posteriori truths, however, we can say that under appropriate qualitatively identical evidential situations, an appropriate corresponding qualitative statement might have been false.... The inaccurate statement that Hesperus might have turned out not to be Phosphorus should be replaced by the true contingency ... two distinct bodies might have occupied, in the morning and evening, respectively, the very positions actually occupied by Hesperus- Phosphorus-Venus.