 It is a commonplace to say that, while the Ten Modes, as presented in Sextus, are concerned with conflicting appearances, the Five Modes are about argument or proof. In these modes, the skeptics develop strategies by which to attack theories that the dogmatists defend. If this is how we characterize the Modes, Aristotle’s objection (section 2.3) immediately comes to mind. Do the Five Modes reveal the skeptic’s lack of understanding because they presuppose that everything is subject to proof? (Barnes 1990; Hankinson 1995, 182–92; Long 2006, ch.3) The three so-called formal modes—Regress, Hypothesis, and Circularity—can be construed in this fashion: when employing them, the skeptic can argue that every premise must be supported by argument; if it is not so supported, the theory begins from a mere hypothesis (on earlier uses of the term hupothesis in Plato and in medicine, cf. Cooper 2002 [2004a]); or it is ultimately circular.