 The phrase may be of 19th-century coinage, but there were obviously ethics of belief well before Clifford and James. Descartes says in the Meditations that when forming a judgment, “it is clear by the natural light that perception of the intellect should always precede (praecedere semper debere) the determination of the will” (1641, 7:60). In the context of a search for certain knowledge (scientia), Descartes maintains, we have the obligation to withhold assent from all propositions whose truth we do not clearly and distinctly perceive (clear and distinct perceptions themselves, by contrast, will produce belief ineluctably). In other contexts, it may be both permissible and prudent to form a mere “opinion” (opinio) whose truth we do not clearly and distinctly perceive. Even then, however, we are obliged to have some sort of evidence before giving our assent. Thus Descartes advises Elizabeth that “though we cannot have certain demonstrations of everything, still we must take sides, and in matters of custom embrace the opinions that seem the most probable, so that we may never be irresolute when we need to act” (1645, 4:295, my emphasis). 