The contributions of Peirce’s scientific work to his philosophy have not heretofore been noticed. His psychological experiments extended the realm of admitted observation: by making putative observations, finding that they agree and that their agreement can be explained by what is putatively observed, what was putative is verified. There is no empirical knowledge without metaphysical but fallible presuppositions; they can only be confirmed by the success of the observations they permit. Peirce expanded empiricism in two directions, both surprising. His astronomical work, ranking stars by order of magnitude, required careful attention to one’s own sensations: interpersonal agreement in that ranking suggested the possibility of phenomenology. And the impressionistic ranking of stars’ magnitudes became the model for Peirce’s idea of normative science. The seemingly oddest of his studies, the ’Great Men Study’, provided evidence that normative impressions, as they agree, are observations. It remained only to make the presumed metaphysics intelligible.

Peirce’s concept of science entails that normative judgment in science, about which types of theory or explanation or evidence, etc., are good, must depend on the evidence provided by the experience of inquiring (Chapter 2), a thesis supported by the history of science (Chapter 3). This implies a method, at once empirical and normative, which Peirce’s late sketch of a trio of ’normative sciences’ (aesthetics, ethics, logic) generalizes and rationalizes. Its generalization is supported by Peirce’s expansion of empiricism (Chapter 7), and its rationalization depends on the rediscovery of final causation (Chapter 6). Although sketchy, Peirce’s idea of normative sciences is important; for its plausibility undermines that most pernicious of dichotomies, of fact and value. This chapter explicates Peirce’s idea of normative science, traces its method from Schiller’s aesthetics through Kant’s ethics, and suggests that the rediscovery of final causation corrects what is most problematic in Kant’s metaphysics of morals, viz., its anti-naturalism.