Necessity, Essence, and IndividuationAlan Sidelle's Necessity, Essence, and Individuation is a sustained defense of empiricismor, more generally, conventionalismagainst recent attacks by realists. Sidelle focuses his attention on necessity a posteriori, a kind of necessity which contemporary realists have taken to support realism over empiricism. Turning the tables against the realists, Sidelle argues that if there are in fact truths necessary a posteriori, it is not realism, but rather