The Impossibility of Doubting the Existence of Other Selves

Abstract This chapter defends the Sanity Principle, which states that it is impossible to be sane while doubting the existence of other selves who play a role in one’s life. It grounds this claim in three interconnected requirements: the Certainty Requirement, which holds that pride or shame requires certainty about other selves; the Comparison Requirement, which argues that pride or shame necessarily depends on comparisons with others; and the Pride-and-Shame Requirement, which asserts that sanity itself requires the capacity for pride or shame. The chapter demonstrates that solipsists and uncertain selves cannot meaningfully experience pride, shame, or self-esteem, and thus cannot qualify as fully sane agents. It also engages with objections; clarifies the relation between certainty and belief; and situates the discussion in relation to Hume, Strawson, Nagel, and Sartre. Finally, the chapter concludes that sanity conceptually requires belief in the existence of other selves, thereby rendering radical doubt about them impossible.