This article is about why moral praxis matters, and how it matters. My textual focus is Sartre’s unpublished and undelivered 1965 Cornell Lectures on ‘Morality and History’. In these Lectures, Sartre presents his mature understanding of moral praxis with a degree of systematicity not found elsewhere in his writings on the topic. Staying close to the idiom of the lectures, then, I discuss the materiality of the ‘ethical normative,’ and the historical efficacy of ‘moral conducts’. The discussion moves from a phenomenological account of normativity, temporality, and creativity, to a dialectical account of their generative interaction, which Sartre names, somewhat ambiguously, ‘ethos’. Sartre’s descriptions and analyses paint a picture of ethos as manifest through moral praxis. Moral praxis exists where ethical exigencies are taken up across time through creative invention, and ethos, as manifest moral praxis, results (for good or ill) in a transformation of the practical field.