Rethinking Deduction Five of Plato’s Parmenides (160b5-163b6)

Abstract

The fifth “deduction” in Plato’s Parmenides (160b5-163b6) concerns the consequences that follow for a (or the) one from the hypothesis that it is not. I argue that the subject of this hypothesis is, effectively, any Form, considered just insofar as it is one Form. The hypothesis, I further argue, does not concern any essential aspect of a Form, but rather posits its contingent non-instantation (“a one is not” = “a Form is not instantiated”). The motion this deduction attributes to its one is a special type of motion: motion into and out of instantiation.