Closure, Underdetermination and the peculiarity of Sceptical scenarios

Abstract Epistemologists understand radical scepticism as arising from two principles: closure and underdetermination. Both possess intuitive prima facie support for their endorsement. Understanding how they engender scepticism is crucial for any reasonable anti‐sceptical attempt. The contemporary discussion has focused on elucidating the relationship between them to ascertain whether they establish distinct sceptical questions and which of the two constitutes the ultimately fundamental threat. Major contributions to this debate are due to Brueckner, Cohen and Pritchard. This contribution aims at defending Brueckner's contention that underdetermination expresses the fundamental sceptical threat and that the closure‐based argument can ultimately be reduced to it, at least concerning sceptical contexts. This will be achieved by undermining Cohen's objections to Brueckner on both counts. Cohen's argument endorses a picture of evidential underdetermination, which, while apt for non‐sceptical contexts, cannot be applied to radical scepticism. A comparison with a case of scientific underdetermination is developed to argue for this idea. Our argument is then applied to the principle equivalence issue and to objections against it. It is then shown how this analysis possesses a distinctive effect on our understanding of the sceptical threat and the assessment of successful anti‐sceptical strategies.