Reasons for Doubting the Existence of Other Selves

Abstract This chapter defends skepticism about the external world, including other selves, by distinguishing between knowledge and rational certainty of the truth. It explains that skepticism does not necessarily involve doubt but denies the possibility of rational certainty, a stance consistent with Moore’s and Nagel’s insights, while creating a deep conflict with the previous chapter’s claim that sanity requires certainty. The chapter contrasts skepticism about perception with skepticism about reason and memory, showing that perceptual beliefs are uniquely vulnerable to illusion and inference. It develops an empirical probabilistic “dreaming argument,” demonstrates how skeptical reflection leads to a self-undermining evidential loop, and critiques responses such as the Moorean, Austinian, Non-circularity Requirement, Loop, and Bootstrapping principles. Finally, the chapter concludes that although sanity demands certainty about external reality and other selves, rational certainty remains unattainable, leaving skepticism inescapable.