Although C. S. Peirce frequently notes the importance of the branch of logic he designates “rhetoric” or “methodeutic,” he only rarely specifies what this subdivision is meant to involve. This article reassesses the role of methodeutic in Peirce’s classification of the sciences, as well as the methodical significance of this classificatory endeavor itself. The article argues that the classification of sciences is best comprehended as a distinctive phase of methodeutic investigation, which examines actual manifestations of inquiry as well as abstract principles in crafting a normatively guiding conception of the scientific venture. It is further argued that the strict hierarchy on which Peirce bases his classification needs to be tempered to allow for a more flexible ordering, in which so-called “dynamical relationships” between inquiries are considered alongside the top-down perspective of “rational precedence.”