Stefan Sienkiewicz. Five Modes of Scepticism: Sextus Empiricus and the Agrippan Modes. Oxford: Oxford University Press, 2019. Pp. x + 204. Cloth, $65.00. This book, which originated as the author's 2013 Oxford dissertation, treats five modes of argument described by the Pyrrhonian skeptic Sextus Empiricus. In the first book of the Outlines of Pyrrhonism (PH), Sextus claims that these modes (disagreement, hypothesis, infinite regression, reciprocity, and relativity) bring about suspension of judgement, a mental state in which one finds the considerations for and against some claim to be balanced. We see the modes used both alone and in combination when Sextus investigates dogmatic philosophy. Accordingly, Sienkiewicz assigns a chapter to each mode and concludes with how they might work together. This book has much to commend it: Sextus's text is clearly explained, distinctions are carefully drawn, the prose is clear, and attention is paid to philological and philosophical issues. Sienkiewicz's main claim is that we must attend to how the modes might make not only the dogmatist suspend judgment, but also the skeptic. This latter task is more difficult, since the skeptic is limited in the beliefs that she can appeal to. Approaching the modes from a skeptical and not dogmatic perspective is important and has never been pursued in depth. Sienkiewicz's essential idea is to conceive of these modes as argument schemata about a given proposition, for instance, the mode of disagreement: "(i) There is peer disagreement over P. (ii) If there is peer disagreement over P, then S should suspend judgement over P. Therefore, (iii) S should suspend judgement over P." (29) Sienkiewicz then asks if the skeptic, given her lack of beliefs, is entitled to believe (i), (ii), or (iii) for any P. In this case, he argues that, since (ii) is a controversial claim in contemporary epistemology, held on the basis of argument, a Pyrrhonian skeptic cannot believe it and cannot use it in the argument to establish suspension of judgement, according to any interpretation of skeptical belief. For four modes, Sienkiewicz argues that the skeptical mode involves opposing arguments. The main problem facing this interpretation is that Sextus only mentions oppositions for two modes. Sienkiewicz thinks this is the only permissible way for the skeptic to employ these modes. Were that true, it would give some support for his interpretation. But Sienkiewicz says that, even with the skeptical versions of the modes, the mature skeptic does not believe the conclusion that she ought to suspend judgment on the basis of rational argumentation from the premises. Instead, the skeptic suspends judgment due to a "disposition" to do so that was developed when she was a "proto-skeptic" (45–46) and still felt rationally compelled to draw such conclusions. But once we say this about skeptical modes, we can say the same thing about dogmatic modes. The mature skeptic has a disposition to suspend judgement in accordance with the modes even though she does not believe the premises or conclusion. If that is so, we can retain the "dogmatic" versions of the modes when they fit the text and no longer need to resort to filling in imagined gaps in Sextus's argumentation. Indeed, so long as the premises are true, even if the skeptic does not believe them, suspension of judgement might be warranted. Something must be said about the relationship between this book and Jonathan Barnes's justly celebrated Toils of Scepticism (Cambridge, 1990), which it structurally mirrors and alludes to even to the point of illustrating an undecided disagreement with a debate about Aristotle's ethical works and ending with a joke about suspending judgment. At many points, Sienkiewicz surely corrects Barnes's readings. Sienkiewicz is also to be commended for incorporating the mode of relativity, which is conspicuously absent in Barnes, even though Sienkiewicz thinks that in the end it is inconsistent with the mode of disagreement. However, both largely put to one side the question of the historical roots of these modes, how they relate to other sets of modes in the Pyrrhonian tradition, and how they are systematically applied outside of PH I. These questions remain largely terra incognita, and Sienkiewicz might have done well to step outside of Barnes's shadow by treating some of them. I close with two areas where Barnes's treatment of the modes clearly surpasses Sienkiewicz's, not because they are faults only with the latter, but because much contemporary scholarship disappoints in this regard. First, Barnes prefaces his discussion of each mode and the system as a whole by reference to an enormous variety of ancient texts by philosophers, physicians, orators, and satirists. This cast of characters is absent from Sienkiewicz, and his discussion loses richness for it. Second, Sienkiewicz takes no note of modern scholarship written in languages other than English, despite the fact that Barnes himself engages deeply with Karel Janácek and Victor Brochard. For these two reasons, although Sienkiewicz makes a valuable contribution to the literature, this book does not supplant that of Barnes. JUSTIN VLASITS Eberhard Karls Universität Tübingen