Sextus Empiricus' Outlines of Pyrrhonism is one of the most important and influential texts in the history of Greek philosophy. In The Demands of Reason Casey Perin examines those aspects of Pyrrhonian Scepticism as Sextus describes it in the Outlines that are of special philosophical significance: its commitment to the search for truth and to certain principles of rationality, its scope, and its consequences for action and agency. Perin argues that the Sceptic is engaged in the search for truth and that since this is so, the Sceptic aims to satisfy certain basic rational requirements. He explains how the fact that the Sceptic has this aim makes it necessary, as Sextus says it is, for the Sceptic to suspend judgment under certain conditions. Perin defends an interpretation of the scope of Scepticism according to which the Sceptic has no beliefs about how things are rather than merely appear to him to be. He then explores whether, and how, Sextus can respond to the objection that since the Sceptic lacks beliefs of this kind, he cannot act and Scepticism is not, as Sextus claims it is, a possible way of life.