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It is generally accepted that skeptical scenarios must be possible to raise legitimate skeptical doubt. I argue that if the possibility in question is supposed to be genuine metaphysical possibility, the skeptic's reasoning does not straightforwardly succeed. I first motivate the metaphysical possibility requirement on skeptical scenarios: it's a plausible position that several authors accept and that a family of prominent views-sensitivity, safety, relevant alternatives-are committed to. I argue that plausible constraints in modal epistemology show that justification for believing that certain global skeptical scenarios are metaphysically possible rests on some justified beliefs about the external world, and that this undermines the skeptical argument. While there may still be local skeptical challenges, skeptics cannot appeal to the metaphysical possibility of skeptical scenarios to generate global external world skepticism.Consider this picture of the skeptical dilemma: Descartes sits in his armchair, wondering what the world is like, and worried whether it is as it seems to be. He realizes that there are many ways the world could bemany possible ways for the world to be-that he lacks the resources to choose between. Since all the possibilities he is considering include his having experiences like the ones he has actually had, experience cannot help choose between them.In this paper I argue that if the purported possibilities in the above picture are supposed to be genuine metaphysical possibilities, this line of skeptical reasoning does not straightforwardly succeed. The above sketch assumes that Descartes can know the metaphysically possible ways the world might be from the armchair. 1 That assumption raises questions about modal epistemologyconceivability and possibility, intuitions about possibility-that have received extensive treatment in the philosophy of mind literature. I argue that plausible constraints in modal epistemology show that justification for believing that certain global skeptical scenarios are metaphysically possible rests on some justified beliefs about the external world, and that this undermines the skeptical argument. While there may still be local skeptical challenges, skeptics cannot appeal to the metaphysical possibility of skeptical scenarios to generate global external world skepticism.

Recently in epistemology a number of authors have mounted Bayesian objections to dogmatism. These objections depend on a Bayesian principle of evidential confirmation: Evidence E confirms hypothesis H just in case Pr(H|E) > Pr(H). I argue using Keynes' and Knight's distinction between risk and uncertainty that the Bayesian principle fails to accommodate the intuitive notion of having no reason to believe. Consider as an example an unfamiliar card game: at first, since you're unfamiliar with the game, you assign credences based on the indifference principle. Later you learn how the game works and discover that the odds dictate you assign the very same credences. Examples like this show that if you initially have no reason to believe H, then intuitively E can give you reason to believe H even though Pr(H|E) ≤ Pr(H). I show that without the principle, the objections to dogmatism fail.Keywords Epistemology · Bayesianism · Confirmation · Evidence · Foundationalism · Dogmatism Epistemology concerns both the nature of epistemic justification but also the lack thereof. On many understandings of epistemic justification, justification requires reasons; epistemologists are therefore also interested in the notion of having no reason to believe that P. It is this intuitive notion that I examine in this paper.Recently in epistemology there has been a resurgence of interest in applying formal methods to epistemological problems. To evaluate these applications we need a clear understanding of the ingredient intuitive epistemic notions, like having no reason. For instance, Bayesian epistemology operates under the assumption that rational belief and evidential confirmation are successfully modeled using Bayesian probability theory.