The purpose of this paper is to offer a distinct contribution to recent attempts to understand Peirce’s normative thinking. Scholars have interpreted the real tensions in Peirce’s normative thought by conflating passages from different moments in the development of his philosophy. Extracts from Peirce’s famous 1898 lectures (when he dismissed ethics as useless) are frequently combined with later passages from 1902 onwards, when he changed his mind. This paper proceeds by tracing the growth of Peirce’s thinking about ethics and correlating (...) his conflicting positions with his theory of the categories. The approach offered here is diachronic. A diachronic approach is necessary to correct some efforts to resolve the inconsistencies in Peirce’s moral theory. Also, a categorical account is understood as essential to perceive the inner coherence of his moral philosophy and to support the view that Peirce moved from a nominalist to a realist position in ethics. By connecting Peirce’s conceptions of ethics to his theory of the categories I hope to have provided a better understanding of the structure of his normative realism. (shrink)