  Diodorus’ definition of that which is possible can be split into two distinct claims: first that everything that either is or will be true is possible, and second, that everything that is possible either is or will be true. The first statement was not questioned by Hellenistic philosophers. It is the second statement that was and is considered counterintuitive and in need of justification; it is this claim which Diodorus attempted to back up with his Master Argument (Alexander, On Aristotle's Prior Analytics 183.34-184.6; Epictetus, Dissertations 2.19).