Philosophy is traditionally conceived as a quest for knowledge and especially for the best kind of it. Given how important this quest is, the skeptic’s questioning of our very ability to generate knowledge constitutes the most formidable challenge against the possibility of philosophy. Sextus Empiricus masterfully describes the way in which ancient philosophers felt attracted by skepticism: “Men of talent, desire to find a way out of the troubling disorder of things in the world that presents them with innumerable conflicts—of appearances, thoughts, and doctrines. They turn to philosophy to settle those conflicts but find themselves time after time in a situation (…) where the reasons for all of a set of conflicting views seem to be of equal weight, so that they cannot decide among themFootnote 1”.

Skepticism has had a long-standing appeal for philosophers since the days of Pyrrho of Elis. From Pyrrho’s time, the major controversies between philosophical schools have often been defined by skeptical arguments. This is illustrated by the debates between Epicureans, Stoics and Academics in Hellenistic philosophy, and perhaps even more so since the rediscovery of Pyrrhonism in Modernity, a period that was remarkably well-researched by Richard PopkinFootnote 2. Even in the Middle Ages, a time in which it was long considered that the problem of radical skepticism was conspicuously absent, recent historiography has shown that the discussion of skeptical arguments played a central role in epistemological debatesFootnote 3.

Skepticism itself has evolved across history. Starting as an attitude aimed at improving the quality of life by upholding the suspension of judgement, it developed into a larger set of arguments and ideas apt to undermine the very possibility of knowledge. Troubled by this prospect, philosophers like Epicurus, the Stoics, Augustine, Descartes, Reid, Kant, Hegel, G.E. Moore and Wittgenstein dealt with some varieties of radical skepticism. They came to realize that the most radical forms of skepticism had the potential to unsettle the very foundations of the philosophical quest. Yet their responses—developed in times and contexts different from our own—may not have all been equally successful. For one thing, Descartes’ discussion of evil demon scenarios, initially intended to provide an absolute foundation for certainty, is considered by many as having fuelled skeptical considerations and as being one of the main avenues for skeptical overtures in modern philosophy. Similarly, it has sometimes been argued that the Common Sense response to Humean skepticism defended by Thomas Reid and the Scottish school of Common Sense grounded knowledge in a blind and irrational instinct that conceded too much to Hume’s skeptical claims.

Yet the limits of some anti-skeptical strategies do not entail that skepticism cannot be successfully dealt with. To reveal the failure of skepticism, the so-called “particularists”Footnote 4 have often pointed to the knowability of the world. Generally, scientists, philosophers, and theologians have assumed that the world is knowable, and that there are many things that we do in fact know. Arguably, this conviction has paved the way for the scientific and technological revolutions of the last centuries. Likewise, if philosophy and theology had not previously asked major questions about the cosmos, human beings, and God, many of the claims of skepticism would be probably contextually void, for they were crafted to dampen the untrammelled aspirations of dogmatism. Yet in practice, the skeptic is no less confident in the power of knowledge and reason than the dogmatic. In this respect, Hume ironically referred to the “extravagant attempt of the sceptics to destroy reason by argument and ratiocination; yet is this the grand scope of all their enquiries and disputesFootnote 5”.

Unlike ancient skepticism, modern and contemporary skepticisms are epistemological theories. These theories can be said to be, in many senses, epistemological theories that throw into question the possibility of knowledge or justified belief. Yet they do so to teach us something about the visible limits of cognition. In this way, current skepticism has become part and parcel of epistemology, or of a particular branch of it. Perhaps this idea might be illustrated by Wittgenstein’s certainties. He argued that skeptical considerations can only be framed against the backdrop of a set of basic presuppositions about the scope and limits of epistemology that make these considerations meaningful and part of a wider language-game. Wittgenstein held that while certainty is a requisite for doubt, doubt is in turn parasitic on certainty. So, it can be said that for skeptical doubts to make sense at all other claims must be epistemically warranted. This holds true for contemporary skepticism, and the reason why our rational capacities are generally reliable.

We do not want to minimize the challenges facing the anti-skeptical traditions in their attempt to confront skepticism. Nor do we want to imply that bringing together all existing critiques of skepticism will automatically disprove the skeptic. Yet a substantive step in this direction can be taken if skeptical strategies are reconsidered in light of the best, most innovative, and most appealing anti-skeptical strategies, whether past or present. The goal of this special issue of Topoi is exactly this. And for that, this issue both reassesses the strengths and limits of some anti-skeptical strategies, and those of skepticism itself.

We may divide the articles contained in this issue in two groups: the historical and the topical. Historical articles assess Descartes’, Kant’s, Wittgenstein’s and Davidson’s anti-skeptical strategies, as well as Levinas’ and Cavell’s considerations about the limits of all anti-skeptical arguments. On the other hand, topical articles include discussions of assorted skeptical theories, arguments and stances such as brains-in-vats arguments, skepticism about the external world, about other minds, about our very experiences and assessments—that may be positive or negative. As a result, they represent an extended variety of anti-skeptical strategies that include externalism, self-undermining responses, contextualism or common sense theories. Together, these articles provide us with a mosaic view of the relative strengths and weaknesses of many skeptical and anti-skeptical strategies.

This issue opens with François-Xavier de Peretti’s “Stop Doubting with Descartes”, which assesses the most prominent anti-skeptical strategy of modern philosophy, namely Descartes’ cogito. According to de Peretti’s interpretation, Descartes’ response to skepticism relies on a particular kind of faith in reason that is never really put in doubt. It constitutes an undetected blind spot in Descartes’ “hyperbolic” doubt. A historical consequence of this is that Descartes’ strategy can be construed and enlightened in Wittgensteinian terms using the anti-skeptical notion of the necessary “hinges” of doubt. A systematic consequence is that Descartes’ response cannot be taken to be successful as a refutation of the skeptic, but only as a decision or bet to move beyond skeptical doubt.

Dietmar Heidemann’s “Material Dependence and Kant’s Refutation of Idealism” examines two Kantian critiques of skepticism to be found in the Critique of Pure Reason. In one of these, Kant articulates the material dependence of the inner from the outer sense. Kant argues that a skeptic about the external world is forced to accept the existence of the world based on the empirical existence of the skeptic in time—a precondition of her own “I am” awareness. Heidemann puts forward that this overlooked argument, which Kant finds apt to defeat skepticism within certain limits, may be more powerful than Kant believed because he considered all our intellectual concepts necessarily derive from perception, and this dependence reveals an intrinsic link between sensibility and understanding.

Miguel García-Valdecasas’ “Are Wittgenstein’s Hinges Rational World-Pictures? The Groundlessness Theory Reconsidered” carefully analyses Wittgenstein’s notion of hinges, i.e. the basic and fundamental certainties on which knowledge is supposed to rest. In the standard analysis of hinges, these are neither justified nor unjustified and lack any truth-value. Inspired by OC 166, the so-called “groundlessness interpretation” puts hinges outside the realm of JTB epistemology. Yet García-Valdecasas disputes this interpretation for two reasons: it is not based on solid evidence, and it suggests that hinges should be accepted by fiat. But hinges can be seen as illuminating world-pictures that reflect reality and are answerable to facts in a derivative way, being thus continuous with one’s ordinary beliefs. If this is so, hinges are ultimately rational devices, and hence, apt instruments to deal with skepticism.

Nathaniel Goldberg’s “The Systematicity of Davidson’s Anti-skeptical Arguments” can be said to present a very original interpretation of Davidson—an author not standardly recognized as having put forward an anti-skeptical project. Goldberg identifies a connecting thread going through several of his papers and arguments that can ultimately present a coherent and systematic “master argument” against skepticism. In his interpretation, Davidson’s master argument refutes in one fell swoop three kinds of skepticism: solipsism, falsidicalism and conceptual relativism. Though Davidson’s first premise is Cartesian in spirit—the “new cogito”, as Nagel called it, the nerve of his anti-skeptical strategy is semantic, and relies on considerations about the constraints on interpretation.

Alexander Altonji’s “Must Skepticism Remain Refuted? Inheriting Skepticism with Cavell and Levinas” examines Cavell’s and Levinas’ idea that no anti-skeptical argument can claim universal assent. This is based on the idea that skepticism, especially skepticism about other minds, is not restricted to epistemological matters but has important consequences for metaphysics and ethics. One of these is that human finitude and the lack of guarantee about the future intelligibility of phenomena make it difficult to say that our expressions about them will be secured in future contexts. The appeal to metaphysical universals or to social convention cannot ensure the historical transmission of the intelligibility of our expressions. As a result, sharing meaning entails acknowledging each other as a separate source of significance.

John Greco’s “Externalism and the Myth of the Given” reviews objections against two kinds of externalist foundationalism: a response to “no good inference” arguments for skepticism about the external world and a response to skeptical regress arguments. Some of them are objections to foundationalism along the lines of Sellars’ critique of “the given” in “Empiricism and the Philosophy of Mind”. After carefully analysing these objections and their consequences, Greco concludes that they are ineffective against the kind of externalist foundationalism defended, because they either believe perception involves an inference from appearance to reality, or trade on considerations that externalism can ultimately accommodate.

Epistemologists agree that safety and sensitivity accounts of knowledge need to be relativized to a method. However, it is unclear to what method we should attribute a given token belief. Haicheng Zhao’s “Sensitivity, Safety, and Brains in Vats” presents an argument in favor of Nozick’s much maligned “Same-Experience-Same-Method Principle” for determining which methods produce a given token belief. According to Zhao, sensitivity and safety theorists who reject the Same-Experience-Same-Method Principle will wrongly attribute knowledge to individuals when skeptical possibilities are close. If we accept the Same-Experience-Same-Method Principle, however, sensitivity and safety theorists can give the right verdict. Thus, we have some reason for accepting Nozick’s controversial principle.

Genia Schönbaumsfeld’s “Scepticism about Scepticism or the Very Idea of a Global ‘Vat-Language’” argues that we should be skeptics about skepticism. She holds that such skepticism is not inspired by the fact that the skeptic’s doubts about the external world are unrealistic or overblown, but by the fact that we cannot know what the world seems like while being unable to know on the basis of what it is like. If this is true, skepticism about the external world should resolve itself into skepticism about perceptual appearances. If radical skepticism questions these, the radical skeptic is in a predicament, because at a minimum she requires her perceptual appearances to have a content that she can know. By being unable to exploit the alleged discrepancy between how the world appears to her and how it actually is, she even lacks the means to motivate skepticism in the first place.

Joe Milburn’s “Unpossessed Evidence: What’s the Problem?” considers three quasi-skeptical arguments put forward by Nathan Ballantyne: the meta-defeater argument, the overlooked defeater argument, and the doubtful fairness argument. Each of these arguments starts from our awareness of unpossessed evidence concerning a proposition p, and conclude that we have undefeated defeaters for our belief that p. Milburn argues that Ballantyne’s arguments are unsatisfactory in that they fail to express the skeptical problem presented by unpossessed evidence. What matters, according to Milburn, is not an awareness of unpossessed evidence as such, but rather an awareness of unpossessed counter-evidence that respectable inquirers take to justify disagreeing with us.

A Pyrrhonian normative skeptic is someone who believes it is possible that a global normative error theory is true and has suspended judgment on whether it is true or false. Can such a radical skeptic be brought out of their skepticism? Elizabeth O’Neill’s “A Normativity Wager for Skeptics” proposes a new decision problem for Pyrrhonian normative skeptics, which she calls the “normativity wager for skeptics.” In brief, the Pyrrhonian normative skeptic must decide whether or not to attempt to comply with any reasons to which he may be subject. O’Neill argues that considering this decision problem will motivate skeptics to attempt to act in accordance with any normative reasons to which they might be subject, and she considers three ways that this could bring skeptics to give up their skepticism.

One important anti-skeptical strategy to stave off knowledge-skepticism is to accept knowledge-fallibilism. Fallibilists hold that one can know that p while not p is possible given one’s evidence. But fallibilism faces the problem of concessive knowledge attributions (CKAs). When we make a concessive knowledge attribution “I know that p, but maybe p isn’t true”, we seem to be contradicting ourselves. However, fallibilism implies that CKAs are true. In this context, Jacques Vollet’s “Fallibilism and the Certainty Norm of Assertion” argues that fallibilist philosophers should accept the certainty norm of assertion. According to this norm, one should assert p only if one meets the contextual epistemic standards of certainty for p. By accepting the certainty norm of assertion, Vollet argues, fallibilists can give a better pragmatic explanation of the incoherence of CKAs than they can give by relying on standard appeals to Gricean implicature.

Jean-Baptiste Guillon’s “The Dynamic Strategy of Common Sense against Radical Revisionism” develops an anti-skeptical argument situated within the Common-Sense Tradition, one of the most important traditions of anti-skepticism in modern and contemporary philosophy. According to Guillon, this tradition contains different concepts of common sense and different strategies against skepticism. The specific strategy he develops here is one that defines common sense as the “epistemic starting point” of the philosophical enquiry. He tries to show that “radical revisions” of this starting point are very unlikely to be epistemically justified once we accept plausible principles about the rational norms of belief-revision. This “dynamic” strategy of common sense combines elements from Peirce’s “critical common-sensism” and from Moore’s response to Humean and Russellian skepticism.

Jumbly Grindrod’s “Anti-Skepticism Under a Linguistic Guise” presents a critical assessment of a certain family of anti-skeptical strategies, namely those that are framed in linguistic terms. Grindrod shows that strategies apparently as diverse as Austin’s anti-skeptical argument, Contextualism or the “function-first” approach, share the following core intuition (formulated also by Dogramaci): that it is psychologically easier to expect an anti-skeptical result when the question of knowledge is framed as a linguistic question about the extension of the word “know”. Though Grindrod acknowledges the appeal of this intuition, he shows, about the three instances just mentioned, that this kind of strategy in fact does not work. Grindrod also offers an error theory about why we have this illusory intuition in the first place.

Anita Avramides’ “The Sceptic, the Outsider, and Other Minds” holds that the problem of other minds is normally analysed as a corollary of the problem of the external world. Drawing on work by Cavell and Moran, this article argues that the skeptic usually misses an important difference in our concepts of mind and of body. This difference is reflected in her formulation of a problem regarding other minds. In Avramides’ view, an understanding of this key conceptual difference is absent in the work of those who attempt to reply to the skeptic. In this context, this article discusses both inferential and perceptual accounts of our knowledge of other minds, and holds that they fail because of a lack of understanding of the key conceptual difference in our concepts of mind and of body. She develops then an analysis of this error that draws on the work of Edith Stein and Cavell.

We wish to thank the Editorial Board of Topoi, and particularly its Editor-in-Chief, Fabio Paglieri, for having taken an early interest in the topic of this special issue. Some of the articles included in it originated in the LVI Reuniones Filosóficas, the philosophical meetings of the Department of Philosophy of the University of Navarra (Spain) of 2021. Around 70 philosophers from Europe, the United States and other parts of the world took part in it. Drawing on the interest awakened by these meetings, it is to be hoped that other future gatherings give continuity to it.