Master argument Aristotle, in his work On Interpretation, had wrestled with the problem of future contingents. In particular whether one can meaningfully regard future contingents as true or false now, if the future is open, and if so, how? In response, Diodorus maintained that possible was identical with necessary (e.g., not contingent); so that the future is as certain and defined as the past. Alexander of Aphrodisias tells us that Diodorus believed that that alone is possible which either is happening now, or will happen at some future time. When speaking about facts of an unrecorded past, we know well that a given fact either occurred or did not occur, yet without knowing which of the two is true—and therefore we affirm only that the fact may have occurred: so also about the future, either the assertion that a given fact will at some time occur, is positively true, or the assertion that it will never occur, is positively true: the assertion that it may or may not occur some time or other, represents only our ignorance, which of the two is true. That which will never at any time occur, is impossible. Diodorus went on to formulate an argument that became known as the master argument (or ruling argument: ho kurieuôn logos [ὁ κυριεύων λόγος]). The most succinct description of it is provided by Epictetus: The argument called the master argument appears to have been proposed from such principles as these: there is in fact a common contradiction between one another in these three propositions, each two being in contradiction to the third. The propositions are: (1) every past truth must be necessary; (2) that an impossibility does not follow a possibility; (3) something is possible which neither is nor will be true. Diodorus observing this contradiction employed the probative force of the first two for the demonstration of this proposition: That nothing is possible which is not true and never will be. Epictetus' description of the master argument is not in the form as it would have been presented by Diodorus, which makes it difficult to know the precise nature of his argument. To modern logicians, it is not obvious why these three premises are inconsistent, or why the first two should lead to the rejection of the third. Modern interpretations therefore assume that there must have been extra premises in the argument tacitly assumed by Diodorus and