 According to Kripke, our initial surprise at the divergent extensions of a prioricity and necessity should be mitigated on reflection. A prioricity (epistemic necessity) is an epistemological notion: it has to do with what can be known. That is not true of the concept of necessity. (2) is necessary because the atomic number of gold is an essential feature of it, and on the face of it, that has nothing to do with what is known or believed by anyone. This kind of necessity is a metaphysical notion, and we may use the term ‘metaphysical necessity’ to distinguish it more clearly from epistemic necessity.