The Master Argument of the Megarian logician Diodorus Cronos, famous in antiquity,1 has received a considerable amount of attention in the past quarter century. On the one hand, its apparent use of tense-logic and its implications for modal logic have been a source of interest to modern philosophers,2 while on the other, historians of thought have discussed its origin in and connection with the works of other Greek philosophers.3 The aid of both of these groups of critics, moreover, has been enlisted in yet another undertaking?reconstruc ting the Master Argument itself. In this case the goal is to produce a valid argument to Diodorus' conclusion and one employing premisses known in antiquity and which at any rate Diodorus could have used.4 The position in which the ancient sources put us vis ? vis the Master Argument is a tantalizing one. Despite the numerous references to it, no account of the proof is contained in the tradition. Epictetus, however, informs us of the premisses (or, rather, two of the premisses) on which it was based and also its conclusion.