The Parmenides has been unduly overlooked in discussions of hypothesis in Plato. It contains a unique method for testing first principles, a method I call ‘exploring both sides’. The dialogue recommends exploring the consequences of both a hypothesis and its contradictory and thematizes this structure throughout. I challenge the view of Plato’s so-called ‘method of hypothesis’ as an isolated stage in Plato’s development; instead, the evidence of the Parmenides suggests a family of distinct hypothetical methods, each with its own peculiar (...) aim. Exploring both sides is unique both in its structure and in its aim of testing candidate principles. (shrink)