 The Pyrrhonian skeptics sought suspension of judgment as a way of achieving calm (ataraxia) in the face of seemingly intractable disagreement. The Pyrrhonians had a number of ways, or “modes”, to induce suspension of judgment. The importance of Pyrrhonian Skepticism to contemporary epistemology derives primarily from these modes, and in particular from a subset of them referred to collectively as “the modes of Agrippa”. There are five modes associated with Agrippa, but three of them are the most important: the mode of hypothesis (or unsupported assertion), the mode of circularity (“reciprocal”), and the mode of regression to infinity. The three modes of Agrippa function together in the following way. Whenever the dogmatist (Sextus refers to those who are not skeptics as “dogmatists”, and we will follow him in this) asserts his belief in a proposition \(p_1\), the Pyrrhonian will challenge that assertion, asking the dogmatist to justify \(p_1\), to give reasons for thinking that it is true. The dogmatist will then either decline to answer the challenge or adduce another proposition \(p_2\) in support of \(p_1\). If the dogmatist refuses to answer the challenge, the Pyrrhonian will be satisfied that the only justified attitude to take with respect to \(p_1\) is to suspend judgment, because no reason for it has been given (thus appealing to the mode of hypothesis). If the dogmatist adduces another proposition \(p_2\) in support of \(p_1\), then either \(p_2\) will be identical to \(p_1\) or it will be a different proposition. If \(p_2\) is the same proposition as \(p_1\), then the Pyrrhonian will also suspend judgment with respect to \(p_1\), because no proposition can support itself (thus appealing to the mode of circularity). If, on the other hand, \(p_2\) is different from \(p_1\), then the Pyrrhonian will ask the dogmatist to justify his assertion of \(p_2\). And now either the dogmatist offers no reason in support of \(p_2\), or offers \(p_2\) itself or \(p_1\) as a reason, or adduces yet another proposition \(p_3\), different from both \(p_1\) and \(p_2\). If the dogmatist offers no reason for \(p_2\), then the Pyrrhonian will invoke the mode of hypothesis again and suspend judgment in accordance with it; if either \(p_2\) itself or \(p_1\) are offered as reasons to believe in \(p_1\), then the Pyrrhonian will invoke the mode of circularity and suspend judgment in accordance with it (because not only can no proposition be a reason for believing in itself, but also no genuine chain of reasons can loop); and, finally, if the dogmatist offers yet another proposition \(p_3\), different from both \(p_1\) and \(p_2\), as a reason to believe \(p_2\), then the same three possibilities that arose with respect to \(p_2\) will arise with respect to \(p_3\). The dogmatist will not be able to continue offering different propositions in response to the Pyrrhonian challenge forever—eventually, either no reason will be offered, or a proposition that has already made an appearance will be mentioned again. The Pyrrhonian refers to this impossibility of actually offering a different proposition each time a reason is needed as “the mode of infinite regression”. The three Pyrrhonian modes, then, work in tandem in order to induce suspension of judgment with respect to any proposition whatsoever.