Pyrrhonism and the Dialectical Methods: The Aims and Argument of PH II1* Justin Vlasits 1. Introduction The Pyrrhonian skeptics occupy a paradoxical place in the history of "philosophical inquiry". On the one hand, they are the only school that self-consciously defined themselves as inquirers, this being, of course, the root meaning of σκεπτικός.2 Moreover, they developed many τροποί or "modes" in order to conduct that inquiry. So surely, Sextus Empiricus, the only member of that tradition from whom we possess complete works, should be the star of the show when we talk about ancient conceptions of modes of inquiry. On the other hand, he has also been accused of not really being an inquirer at all. Pyrrhonian inquiry is a sham. According to Jonathan Barnes, for instance, "real Sextan sceptics do not investigate"3 and as Gisela Striker says, "contrary to Sextus' initial claim that the Sceptic goes on investigating, philosophical investigations seem to be precisely what the Sceptic's way of life is designed to avoid."4 The way that this objection is normally formulated, the question is whether it is possible for a Pyrrhonian to inquire at all, given their suspension of judgement and argumentative techniques. Sextus directly answers a version of this objection in a number of passages.5 A related, but less familiar, objection might grant that there is some kind of inquiry that the skeptic can engage in, but that they don't inquire in the right way and this is the reason that their inquiry never gets anywhere. R.J. Hankinson, for instance, has described skeptical investigation as "a gentle sort of pottering about comparing and contrasting things."6 According to this objection, if one were to really inquire in the right way, doing more than "pottering about", one would not end up like a Pyrrhonist but like a dogmatist of one sort or another. The plausibility of this dogmatist response seems to directly hinge on whether they can say what "the right way" is, that is, if they can give us a methodology, an account of the correct method of inquiry, which is able to say that dogmatists end up at their dogmata by inquiring in the right way while skeptics have the problems they have because they are not inquiring in the right way. The dogmatist should be able to specify how one should go about inquiring such that 1) one is inquiring rationally or correctly, and 2) one ends up not as a Pyrrhonian who still suspends judgement and inquires, but as a person holding whatever dogmata they should be holding. That is, in order to make this objection stick, the dogmatist needs to show that he has reliable methods for discovering the truth. If the dogmatist cannot do this, and the Pyrrhonist 1* Versions of this paper were presented in Bochum (via Skype), Tübingen, and London, where I profited greatly from the comments by Klaus Corcilius, Jim Hankinson, Pieter Sjoerd Hasper, Federica González-Luna, Julia Pfefferkorn, Vasilis Politis, Johanna Schmitt, Mark Textor, and Máté Veres. Special thanks are due to Mike Arsenault, Kristian Larsen, Philipp Steinkrüger, Katja Vogt and two anonymous reviewers for extensive comments on (at least!) one version of the paper. 2 Barnes 2007, Striker 2001, Vogt 2012. 3 Barnes 2007, 327. 4 Striker 2001, 121. 5 See PH II.1-12, M 8.337–332a, and Palmer 2000, Perin 2010, Vogt 2012, Fine 2014. 6 Hankinson 1995, 299. can specify a plausible way of inquiring through the modes that leads to continued inquiry and suspension of judgement, then it seems like the dogmatic objection doesn't have a leg to stand on. Fortunately for the dogmatists of all stripes, they do have various things to say about methodology, broadly construed. While it is controversial exactly when the study of methodology begins in antiquity, there is no question that by the time of Sextus, authors from Epicurus to Galen had made methodology a central part of their epistemological projects.7 The thesis of this paper is that Sextus has a response to the dogmatic objection suggested above: there is a single continuous line of argument that runs through the second book of the Outlines of Pyrrhonism (PH) to the conclusion that one ought to suspend judgement on the reliability of dogmatic methodologies. If successful, this argument undercuts the dogmatic objection by showing that the methodologies they are pointing to are themselves puzzling and need to be investigated. He does not meet the challenge by claiming that skeptical inquiry is methodical- this would be dogmatizing in a way that is clearly unacceptable to Sextus. Rather, he shows that the very distinction between methodical and unmethodical inquiry that the dogmatic objection relies upon is deeply puzzling and itself the subject to further inquiry. Without a firm handle on what constitutes reliable, methodical inquiry, one is not in a position to say whether or not someone else is inquiring methodically. This constitutes an indirect, but nevertheless sufficient response to the dogmatist challenge. Showing that the objection makes a presupposition to which they are not entitled is enough to disarm that objection. I show below how this single argument structures and unifies PH II. This book is more than merely a skeptical inquiry into various topics dogmatists classify under "logic". It does contain such an inquiry, but as part of a bigger project to undercut the objection from dogmatic methods. The significance of this thesis is not merely limited to giving us a better understanding of Sextus' treatment of logic. If successful, this thesis will open up a new way of approaching Sextus' works more generally. Most work on Sextan Pyrrhonism has focused either on the first book of PH, on isolated arguments in the rest of the corpus, or occasionally on general themes and argumentative strategies of a book.8 As far as I am aware, there has been no attempt to detect a single, unified line of argument in anything like an entire book of Sextus.9 In this paper, I will thus try to do two things: show that there is the unity to PH II that I am suggesting and that this unity is geared towards responding to the dogmatic objection about methodology.10 The plan for this paper is as follows. First, I will give some background to the debate between Pyrrhonism and dogmatism and develop in more detail the dogmatist objection to Pyrrhonism 7 For Epicurus, see Asmis 1984 and Allen 2001. For Galen, Frede 1987. 8 On Against the Ethicists, see Bett (1997). For Against the Physicists, Bett (2012) and Algra and Ierodiakonou (2015). For Against the Musicians, Bett (2013). For Against the Arithmeticians, see Brisson (2006) and Corti (forthcoming). Bett (2005)'s argument breakdown of Against the Logicians is a useful comparison for my own project. While I follow Bett in his breakdown of the series of topics, I go beyond Bett in showing that there is a single argument that runs through this series of topics. Compare also the discontinuities in the argument of M IX and X noted by Algra and Ierodiakonou (2015). 9 The closest attempts to my own are Hankinson 1998 and Thorsrud 2009, who each give a unified account of the criterion-sign-proof sections. 10 I leave open whether other works of Sextus can contribute in some indirect way towards responding to the dogmatic objection, for instance, by making his own inquiries conform to the dogmatic conception of methodical inquiry. My main aim is to say that PH II is the place where we get a direct response. that PH II is an answer to. I will argue that Sextus criticizes particular dogmatic methodologies in a rather understudied portion of PH (II.193-259). I then uncover an implicit "master argument" against dogmatic methodology in the discussion of the criterion-sign-proof that occupies the majority of PH II. Then I will briefly connect this argument with the introduction to PH II on the possibility of skeptical inquiry. I proceed backwards throughout the book, since its methodological focus is clearer in the later sections than the earlier. I will conclude by connecting the project of PH II to Sextus' overall outlook. 2. Pyrrhonism and Dogmatism Sextus takes Pyrrhonists as committed to inquiry, as opposed to dogmatists, who think that inquiry is already at an end: [T1] When people are investigating any subject, the likely result is either a discovery, or a denial of discovery and a confession of inapprehensibility, or else a continuation of the investigation. This, no doubt, is why in the case of philosophical investigations, too, some have said that they have discovered the truth, some have asserted that it cannot be apprehended, and others are still investigating. Those who are called Dogmatists in the proper sense of the word think that they have discovered the truth- for example, the schools of Aristotle and Epicurus and the Stoics, and some others. The schools of Clitomachus and Carneades, and the other Academics, have asserted that things cannot be apprehended. And the Sceptics are still investigating. (PH I.1-3)11 According to the Pyrrhonists, inquiry is a matter of opposing considerations (of things thought and things observed) and their way of doing this is with the various sets of modes. In the skeptic's experience, use of these modes has led to suspension of judgement and then to tranquility. So we might read his way of distinguishing skeptics from dogmatists in a variety of ways. Most generally, the dogmatist could be said no longer to do any sort of inquiry at all, even inquiry of a different sort from what the skeptic does. Another, more specific option, would be to say that the dogmatist doesn't oppose considerations in their inquiry. Finally, the dogmatist might not use those particular modes. The text above seems to suggest the most general interpretation. Dogmatists, it seems, are just those who no longer inquire tout court. However, we might think there is something unfair about this characterization of dogmatism.12 Dogmatists do agree that one should be an inquirer-they just think that if you inquire properly, you won't end up suspending judgement. That is, it evidently does not follow from one being skeptikos, or even from the idea that inquiry requires coming up with considerations for and against, or even coming up with considerations through the use of the modes, that one will end up suspending judgement. For one could inquire in such a way as to discover decisive considerations and expose all other considerations as somehow problematic. The fundamental challenge to Pyrrhonism that is considered in this paper is this: why can't properly conducted inquiry lead to discovery? 11 Translations of PH are from Annas and Barnes 2000, occasionally with substantive changes. 12 Barnes 2007, Fine 2014. PH I has no response to this sort of objection-Sextus merely articulates the skeptical way and does not engage with dogmatic methodologies.13 But this is a serious worry, one that should be addressed somewhere in a work like the Outlines. My suggestion is that this is done in PH II, which has as its stated goal the examination of dogmatic logical theory. The idea that the study of methodology would somehow coincide with the study of logic is not a surprising one in this time period. Galen just says "The logical methods have the power of discovering what is investigated" (MM 10, 28-29 Kühn). Here he clearly means by "logical methods" not merely rational methods or something like that, but more narrowly the sort of thing developed by philosophers like Plato, Aristotle, Theophrastus, and even the Stoics, in particular methods of classification and demonstration, because his opponents (the so-called "methodists") do not pay sufficient attention to these philosophers. On Galen's view, knowing logic will help the practicing doctor come up with, inter alia, accounts of diseases and treatments.14 But Galen was not alone in this methodological understanding of logic. Alexander of Aphrodisias claims that logic, in the sense of syllogistic, is the study of various kinds of "method" (In APr 1,3) and claims that the study of syllogistic is important for philosophy "only to the extent that dealing with them [i.e., syllogisms] is useful for demonstration and for the discovery of what is true" (In APr 8,22-25). A middle Platonist such as Alcinous also claims explicitly that dialectic is fundamentally about how one comes to know, in his case, essence and attribute and that the dialectician knows the nature of reality (Didask 156.24-26, 160.4041). Even in the Stoics, dialectic is said to be what makes the wise man infallible in argument and distinguishes true from false (DL 7.47). Although the details of each of these views differed, sometimes in major ways, they all agreed on a tight connection between logic on the one hand and epistemology/methodology on the other. In what follows, I will show how Sextus has a two-pronged response to this line of objection. (i) He challenges the particular methods that have been brought up by dogmatists (syllogistic, induction, division, definition, and sophisms), showing for each of them that we should suspend judgement about whether these methods reliably bring about discovery. (ii) He has an argument that we should suspend judgement about the possibility of dogmatic method as such, by arguing that we should suspend judgement on the existence of presuppositions of method. While many of these passages have been treated in isolation in the past, what is novel about the approach here is that I am interpreting these passages together as a unified response to the dogmatist's objection to Pyrrhonism. These two arguments that Sextus gives, on my interpretation, complement one another. The more general argument has the benefit of applying 13 Indeed, it is plausible that PH as a whole makes room for the possibility that inquiry does result in decisive considerations being uncovered. That is, it does not rule out that one could engage in dogmatically successful inquiry. Nevertheless, I am claiming that only in PH II does Sextus consider the idea that dogmatists inquire methodically as an objection to Pyrrhonism and responds to this objection. Thanks to Jim Hankinson and an anonymous reviewer for pressing me on this issue. 14 See Barnes 1991 for Galen on the use of logic. to methods as of yet unproposed, but it has the disadvantage that it assumes as a premise that all methods presuppose the existence of the criterion of truth, (indicative) signs, and proofs, itself a rather strong assumption. This weakness is ameliorated by the arguments against specific methods, which do not depend on such presuppositions. 3. The Challenge to Dogmatic Methods If we look carefully at the body of PH II, we see it divides into two big sections. After the proem introducing the skeptical discussions of logic, physics, and ethics on the possibility of skeptical inquiry and the right order of inquiry into dogmatic matters (II.1-13), we have a long section on the criterion of truth, sign-inference, and proof (II.14-192) and then a section on what I will call the "dialectical methods" of syllogism, induction, definition, division, and sophisms (II.193-end).15 It has not been recognized in the literature that these constitute two quite different sections and appeal to quite different strategies. So, before discussing the content of each section, I will briefly try to motivate a view about the structure and unity of the book as a whole. In 14-192, the three subsections are linked by a deliberate and very clear strategy that I call "successive concession".16 This strategy originates roughly with Gorgias' On not being, a text Sextus knew well.17 Gorgias' argument, abstracting from the many difficulties, is roughly as follows: l Nothing exists. l If nothing exists, we couldn't know anything. But even if something existed, we could not know it. l If we cannot know what exists, we couldn't communicate it. But even if we could know it, we could not communicate it. On its face, these "even if"s are quite strange. What's the point of these further arguments, once one has been convinced that nothing exists? Certainly no one would dream of saying that we know and communicate things that do not exist. I suggest that this strategy effectively allows Gorgias to do two things simultaneously. First, he indicates the dependence of knowledge on existence and communication on knowledge (and thus also on existence). Thus any problems 15 Mates 1996, by contrast, sees the turn from 192 to 193 to be a shift from Stoic logic to Peripatetic logic. However, Sextus treats the Stoic and Peripatetic theories of syllogism twice: once in the section on proof (Stoic 157-162; Peripatetics 163-166) and once in the section on syllogisms (Peripatetics 195-197; Stoics 198-203). Thorsrud, in his discussion of Sextus on dogmatic logic, simply omits discussion of the sections after proof. Bett 2019, 126-127 makes the contrast between "epistemological" and more formal "logical" topics, but again, many logical topics such as the syllogism receive technical treatment in both sections and, as will be clear below, Sextus' focus at the end of PH II is still epistemological. Still, Bett is right that the basic notions under discussion at the end do not themselves epistemologically loaded in the way that the criterion, sign, and proof are. 16 Hankinson 1998, 194-6 calls it the "Concessive Method" and discusses its structuring role in the discussion of the criterion of truth, sign, and proof. 17 M VII.65-86 and Ps-Aristotle On Melissus, Xenophanes, and Gorgias are our two extent sources on this treatise. for things existing transfer to problems for knowledge and communication. Second, the strategy allows Gorgias to raise independent problems for knowledge or communication. Sextus' skeptical twist on the Gorgianic maneuver structures PH II.14-192: l One should suspend judgement about the existence of the criterion of truth. l If one should suspend judgement about whether there is a criterion of truth, one should suspend on whether there are signs. But even if there were a criterion, one should suspend on there being signs.18 l If one should suspend judgement about whether there are signs, one should suspend on whether there are proofs. But even if there were signs, one should suspend on whether there are proofs.19 Sextus thus replaces Gorgias' denials of existence with suspension of judgement, but the overall strategy is parallel. Sextus can both gradually build up a very powerful set of considerations against the existence of proof and show how these considerations relate to one another. It is not necessary for my purposes here to give a full catalogue of Sextus' arguments in his discussion of the criterion, sign, and proof, although I will return to some important passages in the next section. What is important, however, is to distinguish 14-192 from 193 and following. There are a number of significant differences between these sections and what came before. The first section following upon the discussion of proofs, on syllogism, is introduced with a different kind of transition than the successive concessions that we saw before: [T2] For this reason it is no doubt superfluous to deal with the syllogisms which they talk so much about-they are turned about together with the reality of proofs (for it is plain that if there are no proofs, then probative arguments have no place either) [...] (II.193) On the surface, this seems to be of a piece with the earlier transitions, since Sextus is saying that it is not necessary to continue the discussion because of what came before, even though he will anyway. But what is different here is the reason Sextus gives for doing that. Here the idea is not that, since there are no proofs, there are a fortiori no syllogisms. Sextus has just said quite the opposite of this in PH II.138, 145-167-only some syllogisms are proofs, since proofs unlike syllogisms, must have true premises. Showing that there are no proofs could not in general show that there are no syllogisms, as there could be non-probative syllogisms. Rather, Sextus says, if we suspend on whether there are proofs, we should suspend judgement on whether any syllogisms amount to proofs. More strikingly, perhaps, is the fact that between the sections on syllogism, induction, definition, division, and sophisms, there are no transitions at all. That could either indicate that these are just a bunch of appendices to the main subject of book II or else that, unlike the 18 PH II.95, T7 below. 19 "It is clear from these considerations that proof too is an object of disagreement. If we suspend judgement about signs, and proofs are a sort of sign, then it is necessary to suspend judgement about proofs too. For we shall find that the arguments we propounded about signs can also be applied to proofs[...] But if something must be said about proofs specifically, I shall consider briefly the argument about them..." (PH II.134-5 with omissions). criterion/sign/proof arguments, Sextus does not see any direct relations of dependence between these chapters. I suggest that internal and external evidence points to the latter. On a purely textual level, there is an extraordinary difference between these sections and the previous: none of these sections are paralleled in Against the Logicians, unlike 14-192, for which there is a direct parallel for more than 2/3 of the passages.20 Furthermore, Sextus himself explicitly groups them together: [T3] Since some of the Dogmatists say that dialectic is syllogistic, inductive, definitional, and divisional science and we have already discussed (after the arguments about criterion, sign, and proof) syllogisms and induction as well as definitions, we don't think it out of place to also discuss division briefly. (II.213) In T3 Sextus explicitly marks the sections after proof as being unified by being somehow the sciences that make up "dialectic". In doing so, he follows standard parallel groupings found in roughly contemporary authors. Alcinous, for instance, lists the parts of dialectic as induction, syllogism, division, definition, and analysis (Didask 5). Clement of Alexandria lists induction, division, definition, and demonstration (Stromata VIII.6). Beginning perhaps with Syrianus and Proclus, the list of dialectical methods in late antiquity became standardized as division, definition, demonstration, and analysis (Ammonius In Isagogen 38, 17-20).21 Finally, the lack of transitions does not mean that there are no connections between these texts. The most notable such connection is the method of induction (PH II.204). Sextus presages his discussion of induction in PH II.195-7, which discusses one way of justifying the universal premise of a syllogism. He probably also refers to induction at PH II.210, where he suggests that a definition should be, but cannot be, judged with reference to the "infinite particulars", apparently suggesting that definitions cannot be justified by induction.22 So it seems that we have good reason to conclude that we are dealing with a unified section of text.23 20 For the parallel passages, see Bett 2005, 193-5. 21 Because of the lack of parallels for this sort of grouping in earlier sources and the presence of many parallels in Platonist texts beginning in the 2nd century, it seems reasonable that either Sextus himself or else a recent predecessor is here incorporating new material in response to recent trends in dogmatic philosophy. Because of Galen's polemic against Pyrrhonism (De Lacy 1991) and their common medical background, it is possible that we are seeing a reaction to his methodology. 22 Annas and Barnes 2000 ad loc. 23 Two possible problem texts: the section on common accidents and sophisms appear on neither list nor in any of the parallels. The common accidents section is part of the discussion of division. This is indicated by the fact that Sextus says that the same argument against division of genera into species applies mutandis mutandis to common accidents. Moreover, in Ps-Galen Philosophica Historia 14 and Boethius (drawing on Porphyry drawing on Andronicus of Rhodes) (De divisione 48,26ff.), we know that there was interest in dividing a subject into accidents, which even Aristotle mentions (PA 643a27–31), although he does not discuss it in any detail. Thus it seems most likely that Sextus' arguments against the existence of common accidents is of a piece with his arguments against other universals in division. The section on sophisms is perhaps trickier. There are several possible explanations for this. One is that Galen (cf De Lacy 1991) often called skeptical arguments sophistical, suggesting that one skilled in dialectic would be able to solve them. Another, more general point, is that sophisms might have been considered important for dialecticians to know to defend In these sections, Sextus does not argue that we should suspend judgement about whether there are syllogisms, inductive arguments, etc (as he does with the criterion, sign, and proof) but rather gives arguments to the effect that they are not persuasive, useful, or "scientific". That this is so is especially clear in the section on syllogisms, since he had arguments in the earlier section on proof (II.156 ff) that all the indemonstrable arguments are inconclusive by redundancy and thus not syllogisms at all. Sextus refers to these arguments in T2, but does not repeat them, instead aiming for the weaker conclusion, meaning that Sextus could have perfectly well argued for the stronger conclusion here but chose not to. Here is not the place for detailed reconstructions of his arguments against each of these methods, since our main interest is Sextus' larger argumentation. Here my aim is merely to show that Sextus is arguing for the same sort of conclusion in each of these cases and to tie up some loose ends surrounding two passages that do not seem to fit in with the general program. l PH II.193-203: Syllogisms "have no subsistence" in the sense that they cannot be used to confirm their conclusions, since confirming the major premise just involves confirming something about the relationship between minor premise and conclusion. For example, consider the Stoic first indemonstrable, "If A, B. A. So, B". If you have belief in A, but wondered about whether B, that would mean that one also wondered about "If A, B", since all it is to wonder about the conditional is to wonder whether B follows from A. So conversely, belief of the premises presupposes and thus cannot confirm the conclusion. Sextus' frequent claim in this section that syllogisms have no "subsistence" (ὑπόστασις) seems to mean not that there are no syllogisms in the Stoic/Peripatetic senses, but rather that they do not have the confirmatory power or "weight" that the Stoics and Peripatetics think they have. He does not argue here that, for instance, the first indemonstrable is not a syllogism, but rather assumes that it is and argues that it is epistemically sterile.24 l PH II.204: Induction "totters" (σαλεύεσθαι) because it is impossible to go through all the particulars and only going through some of them is risky (ἀβέβαιος).25 l PH II.205-212: Definitions are not useful for apprehension or teaching as the dogmatists claim, since apprehending the definition of x presupposes that one apprehends x.26 l PH II.213-228: Division is not a "science". Sextus gives different reasons for different varieties of division:27 o PH II.214: Division of words into meanings isn't scientific because meaning is conventional. o PH II.215-218: Division of a whole into parts isn't scientific because we should suspend about whether there are parts of wholes. o PH II.219-227: Division of a genus into species (and species into individuals) isn't scientific because we should suspend about whether there are genera and themselves, while the other methods discussed are more "offensive"-aimed at establishing things one way or another. See, e.g., Alexander In APr 8, 27-29. 24 The problems that Sextus raises here can be usefully compared to the contemporary "scandal of deduction" in Hintikka 1973 and Dummett 1991. 25 See Vlasits (2020) for discussion of Sextus' argument against induction and comparison of it to the Humean problem of induction. 26 This problem is close to the one identified in Geach 1966 as the "Socratic fallacy". 27 For similar accounts of the varieties of division, see Alcinous Didask 5, Galen, PHP IX 9,43 ff, Clement of Alexandria Strom. VIII.6,19 and Boethius De Divisione 6, 17ff. species. Either genera and species are conceptions or else separate substances, but in either case, it is unclear whether they exist. o PH II.228: Division into common attributes has the same problematic ontological implications. l PH II.229-259: Sophisms that can be solved by dialecticians (such as the paradoxes dealt with by the Stoics) are not those that seriously puzzle us. Sophisms that do, such as medical sophisms, can only be solved by those who have mastered the relevant craft.28 As is clear from the very brief summary of these passages, Sextus' strategy for each of these purported methods is to pick out particular features of that method. Then he argues that the presence of these features makes it puzzling whether that method reliably leads to discovery. For instance, division moves from (some kind of) whole to (some kind of) part. Induction is problematic because it is an ampliative inference, while syllogisms are problematic because they are non-ampliative. This strategy, if successful, would make the reliability of any instance of such a method quite puzzling, since any instance would have the problematic feature that Sextus has identified in each of these cases. 4. The Master Argument Against Dogmatic Method So far we have a series of arguments against the reliability of various dogmatic methods. Against Sextus' particular opponents, these arguments should carry some force, insofar as the opponents do presuppose the reliability of these methods.29 On its own, however, this would be a somewhat weak argument-what if I happen to have a new method? Surely it is folly to think that the methods discussed above somehow a priori constitute all the possible methods one might dream up. In this section, I will show how Sextus uses the modes of Agrippa (PH I.164-177) to construct a master argument, designed to induce suspension of judgement about the reliability of any possible method to do what the dogmatists want it to do.30 This would significantly strengthen his argument. 28 For a more thorough treatment of this difficult section, see Schmitt ms. 29 The dogmatic opponent for whom these arguments would carry the least force are the Epicureans, who were widely reputed to be disdainful of dialectic. See, among many places in Cicero, de finibus I.22. Epicurean methodology, so far as we know, did not make extensive use of things such as definitions and syllogisms, but rather forms of sign-inference as attested especially in Philodemus. 30 The modes of Agrippa have received more scholarly attention in contemporary philosophy than almost any other aspect of Pyrrhonian thought. As Williams (1988) has shown, Sextus' use of the modes of Agrippa is largely focused on inducing suspension of judgement about higher-order epistemological claims and is not used as a knock-down argumentative strategy for any topic whatsoever. It is not my aim here either to give a definitive treatment of the modes, Sextus' general attitude towards their use alone or as a network, or their significance in contemporary philosophy. Instead, I will only say enough about them to illuminate Sextus' strategies in the particular passages that I am interested in. See Barnes (1990) for a comprehensive treatment of the modes in Sextus and more recently Bett (2019), ch. 6 for the approach to the modes closest to the one that I favor, although I do not believe much hinges on it for the present discussion. It is worth noting that even Bett, who is concerned with the relationship between the description of the modes in PH I and their application elsewhere in the corpus, only treats PH II.20 of the passages I will be discussing as using multiple modes To have such an argument, we must first reflect somewhat on features of method in general. Galen gives us perhaps the most comprehensive account of the notion in antiquity: [T4] Thus attempting to discover something methodically is opposed to doing so by chance or spontaneously. The method follows a certain route in an orderly way, so that there is a first stage in the inquiry, a second, a third, a fourth, and so on through all of them in order until the investigator arrives at what was at issue at the outset. However, the Empiricists are right when they assert that there is no necessary order, either of discovery or of instruction, for them: experience is unsystematic and irrational, and requires good fortune to arrive at the discovery of what was sought. On the other hand, those who made reason and order the mothers of invention, and who held that there is only one road that leads to the goal, must begin from something agreed by everybody, and proceed from there to the discovery of the rest. (MM 10.31-32 K, trans. Hankinson) This is just one way of thinking about method, influenced both by the philosophical and medical debates of his time-there are undoubtedly others. However, it has the advantage of being relatively precise and sufficiently abstract that it can serve as a general account of method appropriate for philosophy as well as the special sciences ranging from mathematics (Galen's example of a science that uses the correct methodology) to medicine. Moreover, his account is both roughly contemporary with Sextus and reflects an ancient tradition, plausibly extending much farther back than Galen himself.31 From Galen, I think we can isolate three different notions presupposed by any reliable method: (i) A reliable, clear starting point. (ii) A step-by-step way of moving from that starting point to the unclear matter of inquiry. (which Galen calls the "order" for arriving at what is unknown) This consists of: (iia) A revelatory thing. (each previous step in the order in relation to the next step) (iib) A revealing that happens through the revelatory thing. (the movement towards the next step) These seem to be presuppositions of any possible method because, if one is to move step-bystep to come to know x, it is plausible that one needs a reliable place to start and then a way of getting to x from there. It might be thought that one could investigate methodically without recourse to these sorts of notions. Indeed, one might even be able to engage in first order disputes about the methodology of inquiry without these notions. For example, one could in concert. As will become clear, while Bett is completely correct that all four modes are only explicitly used in this passage, I think there are strong enough argumentative parallels between the three main texts to say that they all use the modes. For a contemporary perspective, see Lammenranta (2008). 31 This tradition could even go back as far as Aristotle, whose Posterior Analytics has often been interpreted as containing a guidebook on method. The most famous example of such an interpretation is Jacopo Zabarella, but see more recently, Bronstein 2016. argue, as Aristotle does in Parts of Animals I.2-4, that one shouldn't classify dichotomously as others in the Academy apparently did when one is trying to discover the essences of animal kinds. However, that does not mean that Aristotle isn't committed to the existence of (i), (iia) and (iib). If we should suspend judgement on the existence of any possible reliable starting point for inquiry, then his first order methodological claim that one should not divide dichotomously is undermined together with it. Indeed, it seems to me that only someone who entirely avoids first-order methodology (as Galen claims the Empiricist doctors do) and simply goes about doing one's inquiring can avoid commitment to these notions.32 First, I will suggest that it is plausible to think of the criterion of truth filling the role of (i), signs the role of (iia), and proof the role of (iib). My argument here is restricted to how Sextus conceives of these notions. It is beyond the scope of this paper to show that all the dogmatists share these conceptions.33 Then I will show three related passages in Sextus that together give his "master argument" against method. 4.1. The Criterion of Truth, Sign, and Proof as Methodological Notions We begin with the criterion of truth. There are a number of passages that suggest that, at least according to Sextus, it is meant to be the way by which we grasp what is evident. For example: [T5] Well then, having created so many impasses about the criterion and about what is true, let us inquire after this into the procedures that are constructed, from the criterion, for the apprehension of what is true but does not impinge on us all by itself – that is, sign and demonstration. (M VIII.140, trans. Bett 2005) [T6] Since there is, at the highest level, a dual distinction among things, in terms of which some things are clear, others unclear (clear things being the ones that impinge on the senses and thought all by themselves, and unclear things being those that are not grasped by themselves), our discussion of the criterion, directed toward the impasse over plain things, proceeded according to a sound method (for if the criterion is shown to be infirm, it also becomes impossible to state confidently about apparent things that they are in their nature such as they appear). (M VIII.141-2) [T7] Criteria of truth having appeared perplexing, it is no longer possible to make strong assertions, so far as what is said by the Dogmatists goes, either about what seems to be evident or about what is unclear. For since the Dogmatists deem that they apprehend the latter from what is evident, how, if we are compelled to suspend judgement about what they call evident [= what is grasped through the criterion of truth] could we be bold enough to make any assertion about what is unclear? (PH II.95) These passages strongly suggest that the things judged by the criterion of truth are thought to be "plain" (enargos or prodelos). There are also, however, texts that suggest something slightly different: a criterion of truth is "every technical measure of apprehension of an unclear object" (PH II.15, M VII.33). Brunschwig (1988) has dubbed this the "adelic" conception of the 32 Thanks to Vasilis Politis for pressing me to clarify this issue. 33 The worry that Sextus misunderstands his interlocutors is quite common in the literature on the criterion (e.g., Striker 1974), sign (Allen 2001), and proof (Barnes 1980). Although I cannot fully substantiate this claim here, the framework that I introduced above can, I believe, alleviate many of their worries. criterion and, along with Striker (1974) and others, takes it to be inconsistent with the "prodelic" conception in T5-7. This seems to suggest that we use a criterion to judge unclear objects, not clear ones. However, on the interpretation that I am suggesting, this is not a problem, since the point of the criterion of truth is to enable us to make a move from what is apparent to what is not apparent.34 To say that the criterion of truth is a measure of apprehension is to say that it is the sort of thing that can be used to measure whether other things are true, just as a straightedge is used to measure whether other things are straight. That is, Sextus is here precisely referring to the methodological job description (i) above in his characterization of the criterion of truth. It is supposed to be the clear, reliable, starting point for eventually coming to know things that are unclear. These two conceptions, or better, descriptions, of the criterion are not in conflict on the interpretation in the way that Brunschwig and Striker take them to be.35 Rather, they reflect two different sides of a single methodological role. For something to serve as a measure of the apprehension of something unclear, it seems natural, indeed, that this thing is itself clear. The straightedge is an excellent illustration of this. For its user, it is already clear that the straightedge is straight. This is precisely why the straightedge is useful for checking whether other things are straight. If it weren't so clear that the straightedge is straight, it would in turn require some sort of straightedge. There is also evidence in these same passages that sign and proof are together intended to perform job description (ii). This is clear in T4 where signs and demonstrations are described as "procedures constructed from the criterion for the apprehension of what is true but does not impinge on us all by itself", but also in the continuation of T7: [T8] But for extra good measure, we shall also produce particular objections against unclear objects. And since they are thought to be apprehended and supported through signs and proofs, we shall suggest briefly that it is right to suspend judgement both about signs and about proofs. (PH II.96) But what of the relationship between sign and proof? Sextus repeatedly claims that sign is the genus of proof (PH II.96, 122, 131, 134, M VIII.178, 277, 299), which, he claims justifies the prior investigation of sign, since that is the more generic and fundamental notion. The clearest explanation of what he means can be found in Against the Logicians: [T9] And demonstration is agreed to belong to the genus sign. For it is capable of showing the conclusion, and the conjunction of its premises will be a sign of the conclusion being so. For example, in a case such as "If there is motion, there is void; but there is motion; therefore there is void," the conjunction "<There is motion, and> if there is motion, there is void," being a conjunction of the premises, is also immediately a sign of the conclusion "There is void." (M VIII.277) The idea seems to be that whenever you have a proof such as the void argument, the conjunction of the premises constitutes a sign and so, whenever you have a proof, you have a sign, just as whenever you have a human, you have an animal. There is some disanalogy here, since a sign seems here to be more like a component of a proof than the genus of proof. But either way, 34 Striker 1974. 35 It is notable that neither Striker nor Brunschwig give any arguments for this claim and have suggested elaborate explanations for why these two incompatible conceptions exist side-byside. Presumably, the thought motivating them is simply that nothing is both clear and unclear, so the criterion could not have each as its specific object. Sextus is only suggesting that proof somehow presupposes signs and not vice versa, so we should investigate signs first. This gets some further confirmation from the main accounts of signs and proof that Sextus discusses: those of the Stoics. Sextus reports that a sign is "a pre-antecedent statement in a sound conditional, revelatory of the consequent" (PH II.101, repeated at 104) and a proof as "an argument, by way of agreed assumptions and in virtue of yielding a conclusion, reveals an unclear consequence" (PH II.134).36 On these definitions, it is quite plausible again to understand the conjunction of the premises of a proof as a sign, just as in T9, since the Stoic test for a conclusive argument is the truth of the conditional where the preantecedent is the conjunction of the premises and the consequent is the conclusion. How are we to understand this view? From T9, I suggest, we can see evidence for the interpretation of signs as the (iia) (the revelatory thing) and proofs as (iib) (the revealing that happens through the revelatory thing). For the job of the conjunction of the premises of a demonstration is to be the thing that reveals the unclear conclusion and the proof, when completed with the conclusion, will be an argument that reveals this conclusion. Putting all these pieces together, we have evidence in Sextus that the criterion of truth, sign, and proof, were thought of as playing the methodological roles that I described above. 4.2. The Master Argument Revealed The argument against method, I suggest, is contained in three parallel passages. These argue for the non-existence of the criterion, the (indicative) sign, and proof respectively. One should not take this as a sort of negative dogmatism, however, since Sextus explicitly either gives or refers to what he takes to be equally plausible arguments for the existence of each (PH II.79, 130-133, 185-192). I will quote them all before going through them one at a time. The first passage is in the section about the opening of the discussion of the criterion of truth: [T10a] Again, in order for the dispute that has arisen about criteria to be decided, we must possess an agreed criterion through which we can judge it; and in order for us to possess an agreed criterion, the dispute about criteria must already have been decided. In the background of T10a is the idea that there is a dispute about the criterion of truth, both concerning whether it exists at all and, even if it does, what it is. This is the beginning of Sextus' use of the modes of Agrippa, leading him to seek a way to resolve the dispute. The dispute about what the criterion is (and whether it exists at all) presupposes, he claims, a criterion of truth. This makes quite a lot of sense on the interpretation of the criterion suggested above. If the criterion of truth is a presupposition of a method, then a methodical resolution to any dispute would require the existence of the criterion. Indeed, if we are to appeal to the criterion in resolving the dispute, even more is necessary: we must know what it is. This results in a simple version of the reciprocal mode. 36 See Brunschwig 1980 and Barnes 1980 for the difficulties in Sextus' account of the Stoic definition of proof. The differences do not impact the main claims of this paragraph. [T10b] Thus the argument falls into the reciprocal mode and the discovery of a criterion is blocked-for we do not allow them to assume a criterion by hypothesis, and if they want to judge the criterion by a criterion we throw them into an infinite regress. Sextus rules out in T10b two different things a dogmatist might do to block the reciprocity: either take the existence and identity of the criterion of truth for granted, or try to find another criterion for this criterion. The former is ruled out by the mode of hypothesis-it is not a satisfying way to resolve a dispute about anything to just hypothesize one answer when one could equally hypothesize the opposite. Nor is the latter satisfying, for now we can ask the very same question that we asked about the first criterion of truth. [T10c] Again, since a proof needs a criterion which has been proved and a criterion needs a proof which has been judged, they are thrown into the reciprocal mode. (PH II.20) In T10c, Sextus rules out another strategy. Instead of resolving the dispute about the criterion somehow with one or another criterion, the dogmatist could try to prove that it exists and has a particular character. On the strategy jettisoned in T10b, the dogmatist would be supposing that the criterion of truth's existence and identity were manifest (delon) and thus within the scope of the criterion of truth. On this second strategy, the dogmatist is supposing that it is unclear (adelon), and hence in need of proof. The problem with this strategy, Sextus points out, is that proofs themselves require a criterion. This is not yet fully explained, but have already gotten a hint in PH I.114-7 as to the reason.37 There he claims that proofs, since they are true (that is, sound arguments), must be judged by a criterion of truth. Once that is so, Sextus can use the reciprocal mode once again. The combined force of this dilemma is enough to lead Sextus to suspend judgement about the existence of the criterion of truth, but as we have seen, it is not yet a complete argument because, in particular, he has not motivated his claim that proofs need a criterion. I will suggest that he does this precisely in the section on proof. But first we will examine a parallel argument about signs. This argument, although it does not appeal as transparently to the Modes of Agrippa as T10, has many of the same features and indeed, seems to be implicitly using the modes. [T11a] In addition, there is the following to be said. There has been a dispute among our predecessors, some saying that there are indicative signs, others asserting that nothing is an indicative sign. Now anyone who says that there are indicative signs will speak either simply and without proof, making a mere assertion, or else with proof. Again, just as in T10a, Sextus here refers to the presence of disagreement about the existence of sign. Here he introduces two ways of resolving the disagreement: either the dogmatists merely assert that there are signs, or else they try to prove that there are signs. [T11b] But if he makes a mere assertion he will be unconvincing; and if he wants to give a proof he will take for granted the matter under investigation. For since proof is said to be a species of sign, then as it is controversial whether there are any signs or not, 37 See Barnes (1990), pp. 62-3 for analysis. On his account, this use of the reciprocal mode here is really an instance of the mode from infinite regress. My aim is not to give an analysis of the modes themselves, but only the arguments in which they occur, so this is not important for present purposes. there will be controversy too as to whether there are any proofs or not-just as, if you are investigating, say, whether there are any animals, you are also investigating whether there are any humans; for humans are animals. But it is absurd to try to prove what is under investigation through what is equally under investigation or through itself; therefore no-one will be able by way of a proof to affirm that there are signs. The charge that mere assertion is unconvincing is apparently here a loose way of talking about the mode from hypothesis (cf. T10b). The other option is equivalent to showing there are signs through signs since every proof is a kind of sign. This will involve, again as in T10, a sort of infinite regress, since if every sign is proved by another sign, that in turn will require a sign, etc. [T11c] But if it is not possible to make a firm assertion about signs either simply or with a proof, it is impossible to make an apprehensive assertion about them; and [d] if signs are not accurately apprehended, they will not be said to be significant of anything inasmuch as they themselves are not agreed upon-and for that reason they will not even be signs. Hence in this way too we deduce that signs are non-existent and inconceivable. (PH II.121-123) The first conclusion that Sextus draws from this is the one that we might expect on the basis of T10: it is impossible to make a firm assertion about signs. But in T11d, Sextus infers from this that there are no signs at all. Call this the inference from suspension to unreality. As we shall see, the end of our next text makes the very same claim about proofs-I will delay consideration of this move until we have seen it as well. The final passage stands at the end of the section on proofs. [T12a] Since proof is unclear, then, because of the dispute about it (for disputed items, insofar as they have been subject to dispute, are unclear), it is not manifest in itself but ought to be recommended to us by a proof. Sextus' argument against proof again begins with the mode from disagreement. Here he explicitly claims that the fact of disagreement about the existence and nature of proof is sufficient for saying that proof is, to that extent, unclear. In b, c, and d respectively, he considers three different ways of resolving this disagreement: proof, sign, and the criterion. [T12b] Now the proof through which proof is established will not be agreed upon and manifest (for we are now investigating generally whether there is proof); but, being disputed and unclear, it will need another proof, and that another, and so on ad infinitum. But it is impossible to prove infinitely many things. Therefore, it is impossible to establish that there is proof. Here, like in T10b and T11b, Sextus uses the mode from infinite regress to reject the possibility that proof can be "self-proving", since that would require infinitely many proofs, as each one would require another. [T12c] Nor can it be revealed by way of signs. For, as the question of whether there are signs is being investigated, and since signs require proof to show their own reality, the reciprocal mode turns up, proof needing signs and signs in turn needing proofs-which is absurd. [d] And for the following reasons it is not possible to judge the dispute about proof: the judgement requires a criterion and, as there is an investigation as to whether there are any criteria (as we have established) and criteria therefore need a proof to show that they are criteria, the reciprocal mode of puzzlement is discovered again. Signs and the criterion are both ruled out because they have already been shown to be unclear and in need of proof, hence leading to the reciprocal mode as in T10c. This last point clearly requires something like the arguments of T10 and T11, which aim to connect the notions of the criterion and sign, respectively, to that of proof. Yet it is only here where we really see why this is so problematic, since it was not until this point that we understood that the notion of proof was just as questionable as that of the criterion and the sign. [T12e] If, then, it cannot be suggested either by a proof or by a sign or by a criterion that there is proof, and if proof is not clear in itself, as we have established, then it will be inapprehensible whether there is proof. [f] And for that reason proof will actually be unreal; for proof is thought with the help of proving, and what is not apprehended cannot prove. Hence, there will not actually be proof. (PH II.182-4)38 From this trilemma, Sextus concludes first that it is inapprehensible whether there is proof (T12e) and then makes the suspension to unreality inference in T12f, just as he did in his discussions of signs. These passages display a number of common argumentative techniques that suggest they should be read together. First, they all begin with or imply the existence of disagreement (T10a, T11a, T12a) about the existence and identity of the thing under discussion. This, according to Sextus, should make an inquirer seek a resolution to this disagreement. The plausible ways of resolving the disagreement could either appeal to the thing itself or one of the other methodological presuppositions described by the dogmatist.39 If one tries to appeal to the thing itself, one is thrown into infinite regress or the hypothetical mode (T10b, T11b, T12b), since we are assuming that this thing needs justification already. If one tries to appeal to one of the other three notions, one will eventually end up in either another regress or the reciprocal mode (T10c, T11b, T12c-d). Together, these arguments show that the notions of the criterion of truth, sign, and proof, since they are 1) all unclear (due to the disagreement about what fulfills the roles among dogmatists themselves) and 2) are mutually reliant, none can provide the buck-stopping support for the others. But that doesn't yet show that there is no proof/sign/criterion, just that we don't know whether there is one. But this is the significance of the suspension to unreality inferences in T11d and T12f above. Sextus argues that, if we should suspend judgement about whether there are proofs then proofs do not exist. Why is this? Because proof, being unclear needs to be proved, but in a sense it would also have to do the proving. For this, however, to happen, it would already need to be 38 Compare this passage with M VIII.379-380. 39 Why does Sextus limit himself to only these three options? It seems to be a rather strong assumption that these are the only things that one could appeal to. However, given the job descriptions I have outlined above, I do not think that it is really very implausible that Sextus limits himself in this way. Given the distinction between things that are clear and unclear, and the plausible idea that we must use the latter to grasp the former, there doesn't seem much else necessary for a method. apprehended. The upshot is that proof would need to be known in order to be used and need to be uncontroversial if they will settle any controversies. But nothing of that sort can exist if all its presuppositions are controversial. This step of the argument goes beyond the modes of Agrippa and appeals to features specific to the fact that proof, like the criterion of truth and sign, is a methodological notion. What the modes were able to deliver us with was merely suspension of judgement. The suspension to unreality inferences go strictly beyond this. This argument undermines the whole line of response against the Pyrrhonist. If any account of the proper comportment of inquiry makes presuppositions that themselves need to be subjected to inquiry, that method cannot be used to show the skeptic how to inquire. That is, if one's own methodological views are the subject of continued inquiry, one cannot complain that the skeptic does not use those methods. One could only plausibly make such a claim, it seems to me, if one already knew that one's methods were effective. Importantly, this whole line of argument does not show that there are no good ways to inquire- just that methods of inquiry themselves are to be investigated. So, while this line of argument is sufficient to disarm the dogmatic objection from methodology sketched at the beginning, it does not stop us from inquiring into the existence of various dogmatic methods. This is because Sextus has balancing arguments in favor of their existence: he refers to such arguments for the criterion without giving them (PH II.79) and gives the celebrated self-refutation arguments for signs (PH II.130-133) and for proofs (PH II.185-192). So, even though this particular dogmatic objection does not succeed, there is still, as it were, work to be done on the question. 5. The Possibility of Skeptical Inquiry Thus far, I have argued that Sextus' inquiry into dogmatic logic forms a unified argument. In this section, I will briefly suggest that PH II.1-13, the opening to both books II and III, fits into this story. This passage primarily concerns the possibility of skeptical inquiry into dogmatic issues.40 Sextus there suggests different conceptions of thinking on which it is possible for the skeptic to think about and investigate dogmatic matters as well as going on the offensive and charging that dogmatists are prevented from inquiring because of their commitments. Together these points respond to the dogmatic objection about the possibility of skeptical inquiry and try to shift the burden onto the dogmatists to explain how they can inquire. As I suggested above, we should distinguish between an objection to the possibility of skeptical inquiry as such and the challenge that has thus far been my topic: that skeptics do not inquire with effective methods. However, if what I've said so far is correct, it makes good sense for Sextus to preface his response to the objection about skeptical methodology with this other problem, since this is, in a sense, a more radical worry. If the skeptic cannot inquire at all, then you cannot even raise the question of her doing it correctly or incorrectly. Thus it makes good sense to deal with the possibility-objection before moving on to an objection that grants skeptics can inquire. On my interpretation, the possibility-objection is thus, although logically distinct, a connected question for Sextus. Although this passage stands outside of the treatment of logic proper, it is closely connected thematically to the main body of book II. Moreover, PH II.14 ff supports the two major claims of the proem: skeptics can inquire into dogmatic matters and dogmatists cannot. He shows the 40 The other issue, dealt with much more briefly, is the order in which skeptical inquiry should take place. Because Sextus himself is ambivalent, I will leave this aside. first claim is true in the body of PH II by actually engaging in skeptical inquiry. He shows that dogmatists cannot by showing that their methods are deeply puzzling and one should suspend judgement about their effectiveness. This should suggest that the methods alone are not enough for the dogmatists to confidently reach their conclusions. Rather, what gets the dogmatists to end their inquiries must be something that they have merely presupposed. This suggests, as Sextus indeed says, that having dogmatic beliefs hinders one from fully inquiring. Thus, in addition to the official resolution to the possibility-objection that we find in the opening sections of PH II, we also find support for that same resolution in the logic section proper. 6. Conclusion I have argued that Sextus has a response to the dogmatist objection that skeptical inquiry is unmethodical and, if one inquired methodically, one would end up as a dogmatist. By showing that one should suspend judgement on the reliability of the specific methods proposed by the dogmatists as well as the presuppositions of any possible method, Sextus has indirectly undercut this objection. He has not shown that the skeptic does not merely potter about, to return to Hankinson's phrase. Instead, he shows that the dogmatist's distinction between methodical and unmethodical inquiry is just as controversial as any of the dogmatist's first order philosophical commitments and itself requires investigation. Therefore the dogmatist cannot appeal to it in their challenge without already, as it were, jumping to conclusions. So, even though Sextus has left open the possibility that the skeptic does not inquire methodically, he has nevertheless sufficiently responded to the challenge. This in itself would be quite a result: there is an argument stretching throughout PH II as a whole that undermines an important dogmatic objection. However, Sextus has quietly shown us more than this, for not only has he responded to the dogmatists' objections, but he has done so using the framework of the Pyrrhonian modes of inquiry. Even if he has not said that the modes of skepticism he described in PH I allow him to investigate methodically, he may have been able to show this to the reader. That is, the very fact that the skeptical modes could produce such a searching critique of dogmatic methodology might make one think that, whatever it is the skeptic is doing, she is in fact going about her inquiry in a methodical way. As was said above, Sextus cannot dogmatically assert that his methods are reliable. He can, however, suggest their promise as tools of inquiry by using them to undercut the tools of the dogmatists. The Sextan argument that I have reconstructed here has bearing not only on his attacks against competitors, but also begins to shed some positive light on why one should find Pyrrhonian inquiry attractive in the first place.41 For it, unlike its dogmatic counterparts, does not presuppose its own reliability-when introducing the modes, Sextus himself says "I make no affirmation either about their number or their power-they may be unsound, and there may be more than those I shall describe" (PH I.35). In contrast to dogmatic methodology, skeptical methodology is rather open-minded about itself. It allows one to inquire using these methods into the methods themselves in an unproblematic way. Bibliography 41 See Olfert 2015 for more on the epistemic advantages of being a Pyrrhonist from the perspective of Diogenes Laertius. Algra, K. and Ierodiakonou, K. 2015. Introduction. In: Algra, K. and Ierodiakonou, K. (edd.). Sextus Empiricus and Ancient Physics. Cambridge: Cambridge University Press. Allen, J. 2001. Inference from Signs: Ancient Debates about the Nature of Evidence. Oxford: Clarendon Press. Annas, J. and Barnes, J. 2000. Sextus Empiricus: Outlines of Scepticism. Cambridge: Cambridge University Press. Asmis, E. 1984. Epicurus' Scientific Method. Ithaca: Cornell University Press. Barnes, J. 2007. Sextan Scepticism. In: Scott, D. (ed.). Maieusis: Essays on Ancient Philosophy in Honor of Myles Burnyeat. Oxford: Oxford University Press. Barnes, J. 1991. Galen on Logic and Therapy. In: Durling, R.J. and Kudlien, F. (edd.). Galen's Method of Healing. Leiden: Brill. Barnes, J. 1990. The Toils of Scepticism. Cambridge: Cambridge University Press. Barnes, J. 1980. Proof destroyed. In: Schofield, M., Burnyeat, M.F., and Barnes, J. (edd.). Doubt and Dogmatism. Oxford: Clarendon Press. Bett, R. 1997. Sextus Empiricus: Against the Ethicists. Oxford: Clarendon Press. Bett, R. 2005. Sextus Empiricus: Against the Logicians. Cambridge: Cambridge University Press. Bett, R. 2012. Sextus Empiricus: Against the Physicists. Cambridge: Cambridge University Press. Bett, R. 2013. A Sceptic Looks at Art (but not Very Closely): Sextus Empiricus on Music. International Journal for the Study of Skepticism 3(3): 155-181. Bett, R. 2018. Sextus Empiricus: Against Those in the Disciplines, Oxford: Oxford University Press. Bett, R. 2019. How to be a Pyrrhonist: The Practice and Significance of Pyrrhonian Skepticism. Cambridge: Cambridge University Press. Brisson, L. 2006. Contre les arithméticiens... ou contre ceux qui enseignent que les nombres sont des principes. In: Delattre, J. (ed.). Sur le Contre les professeurs de Sextus Empiricus. Lille: Presses de l'Université de Charles-de-Gaulle-Lille 3. Bronstein, D. 2016. Aristotle on Knowledge and Learning: The Posterior Analytics. Oxford: Oxford University Press. Brunschwig, J. 1980. Proof defined. In: Schofield, M., Burnyeat, M.F., and Barnes, J. (edd.). Doubt and Dogmatism. Oxford: Clarendon Press. Brunschwig, J. 1988. Sextus Empiricus on the kriterion: The Skeptic as conceptual legate. In: Dillon, J.M. and Long, A.A. (edd.). The Question of 'Eclecticism'-Studies in Later Greek Philosophy. Berkeley: University of California Press. Corti, L. forthcoming. Sextus Empiricus: Against the Arithmeticians. Leiden: Brill. De Lacy, P. 1991. Galen's Response to Skepticism. Illinois Classical Studies 16(1/2), 283-306. Dummett, M. 1991. The logical basis of metaphysics. London: Duckworth. Fine, G. 2014. The Possibility of Inquiry: Meno's Paradox from Socrates to Sextus. Oxford: Oxford University Press. Frede, M. 1987. On Galen's Epistemology. In: Nutton, V. (ed.). Galen: Problems and Prospects. London: Wellcome Institute. Geach, P.T. 1966. Plato's Euthyphro: An Analysis and Commentary. Monist 50, 369–82, Hankinson, R.J. 1998. The Sceptics. London: Routledge. Hintikka, J. 1973. Logic, language games and information. Kantian themes in the philosophy of logic. Oxford: Clarendon Press. Lammenranta, M. 2008. The Pyrrhonian Problematic. In: Greco, J. (ed.). The Oxford Handbook of Skepticism. Oxford: Oxford University Press. Magee, J. 1998. Ancii Manlii Severini Boethii De divisione liber. Leiden: Brill. Mates, B. 1996. The Skeptic Way. Oxford: Oxford University Press. Olfert, C.M.M. 2015. Skeptical Investigation and its Perks: Diog. Laert. 9.69-70 and 79-89. In: Vogt, K.M. (ed.). Pyrrhonian Skepticism in Diogenes Laertius. Tübingen: Mohr Siebeck. Palmer, J. 2000. Skeptical Investigation. Ancient Philosophy 20(2), 351-375. Perin, C. 2010. The Demands of Reason: An Essay on Pyrrhonian Scepticism. Oxford: Oxford University Press. Schmitt, J. ms. Sextus on the Expertise Necessary for Solving Sophisms. Striker, G. 1974. Κριτήριον τῆς  Αληθείας. Göttingen: Vandenhoeck & Ruprecht. Striker, G. 2001. Scepticism as a kind of philosophy. Archiv für Geschichte der Philosophie 83(2), 113-129. Thorsrud, H. 2009. Ancient Scepticism. Berkeley: University of California Press. Vlasits, J. 2020. The First Riddle of Induction: Sextus and the Formal Learning Theorists. In: Vogt, K.M. and Vlasits, J. (edd.). Epistemology after Sextus Empiricus. Oxford: Oxford University Press. Vogt, K.M. 2012. Belief and Truth: A Skeptic Reading of Plato. Oxford: Oxford University Press. Williams, M. 1988. Skepticism without Theory. Review of Metaphysics 41(3), 547-588.