I shall argue in this paper that Plato’s so-called method of hypothesis (which he develops mainly in some of his middle dialogues, such the Phaedo and the Republic) is linked with the Platonic metaphysics, in the sense that the main principle of this method is grounded on some of Plato's main metaphysical assumptions. This indicates, I shall conclude, that in Plato epistemology has a metaphysical foundation.