Christopher Hookway presents a series of studies of themes from the work of the great American philosopher Charles S. Peirce (1839-1913), often described as the founder of pragmatism. These themes concern how we are able to investigate the world rationally; and, as Hookway shows, the ideas introduced by Peirce can still make fruitful contributions to research in philosophy, logic and semiotics. After an extended examination of Peirce's account of truth, and of its relations to his ideas about logic, reference, and representation, Hookway discusses his claims that rationality requires a system of 'scientific metaphysics'. The second half of the book studies the role of common sense, sentiments, and emotions in rationality. It concludes with discussions of Peirce's approach to religious belief and the role of pragmatism in his thought. These compelling essays present the fruits of fifteen years of research on Peirce, but do so in a way that makes his ideas accessible and relevant for philosophers who are not specialists in the history of American thought. The introduction offers a general sketch of Peirce's philosophy as a way into the book for such readers, and draws together the themes of the essays.