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 early essays have been thought to frame a grand system later developed more fully (’On a New List of Categories’, 1867) and to provide some of that system’s details (the theory of cognition sketched in three 1868–1869 papers). But the formal structure limned was later understood differently: it is an enduring system in appearance only. These essays suggested though they did not consistently express a conceptual idealism in which true thoughts are distinguished from reality by nothing but their incompleteness – a view later contradicted. Yet, with intentional irony, those same essays were in method empirical. Many have damned Peirce’s writings as fragmentary and contradictory, but these would be faults only were he a system-builder. Instead, his conjectures posed obvious problems and were meant to invite inquiries along diverse and mutually inconsistent lines, in which additions and refinements might be made by which those problems can be solved.

Peirce’s 1890s cosmological speculations were fascinating failures. Their basic idea, that laws require explanation, which could only be by evolution from lawless chaos, was suggested by the success of statistical reasoning in thermodynamics and in Darwinian biology. But the development of that idea was supposed to predict the forms of physical laws not yet discovered, and none of its mutually incompatible developments could do that. In one version, Peirce projected a form of idealism, anti-conceptual and named ’objective’, in which feelings unfelt by any organism are supposed to constitute the material universe; this idealism disappears from later writings. In another version, he projected a ’law of mind’, fundamental to other laws, confused by some commentators with his c.1902 idea of final causation. But such a law and final causation are polar contraries; in showing this, I develop and defend Peirce’s idea of final causation, made use of in Chapter 9.

Modern science is conventionally blamed for the ills of modernity: our hedonism, selfish individualism, and aimless turmoil. Peirce, to the contrary, consistently opposed modern science to modernity, ironically associating it with medieval scholasticism – in anti-individualist method, in realist metaphysics, and in morals. By extending scholastic realism to triadic relations, he could maintain that societies are irreducible to their existing members and, indeed, that persons are social products. In particular, the scientist’s freedom of thought derives from education by and membership in the research community. Restlessness is the one feature of modernity that Peirce embraced: the research community is united in an endless pursuit of truth, hence in a faith that the truth can be known. Science, thus, is a model of selfless devotion to a transcendent, dimly perceived cause. Possibly, this vision was Peirce’s moral motivation; but the several inquiries he initiated, each highly original, resist even such a reduction.

Modern science is systematic inquiry, not systematic knowledge. It cannot be defined by its method or by its metaphysics, since these are amended as inquiry progresses. The norms of science are therefore the business of science and represent empirical discoveries. Peirce’s conception of science is nontechnical and for that reason difficult: he identified it by its ’spirit’, a restless quest for concrete discovery fruitful of further discovery. Theory, then, is no longer the end of inquiry, a resting place, but is, instead, a means to further discovery. Whereas philosophical systems were meant to be coherent and comprehensive, a theory that grounds research cannot be complete and any incoherence in it is a stimulus, not a fatal flaw. But the pursuit of concrete knowledge requires specialization and an evolving network of specialists. Peirce reversed the usual deprecation of specialization: its aim is growth of a knowledge that transcends any individual consciousness.

This chapter summarizes Peirce’s attainments and accomplishments during the period of his scientific career, noting their variety, describing his important contributions to mathematical logic, and mentioning his philosophical essays and lectures, but emphasizing his empirical investigations, which were in experimental psychology as well as in astronomy and geodesy. He improved on such recent developments as Venn’s frequency theory of probability and Boole’s algebra of logic. He studied the histories of science and of logic. I report nothing not already known; this chapter’s purpose is to establish the depth of Peirce’s immersion in modern science, so as to ground the fundamental thesis of this book, that his philosophical modus operandi was that of a scientist. His essays should be read, not as constructing a system, much less as conceptual analysis, but as framing bold conjectures intended to guide the inquiries in which they will be refined and tested, amended or superseded.

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.

Peirce’s c.1902 taxonomy of the sciences is briefly described, stressing its anti-foundationalist formulation. That taxonomy identified philosophy as a science of discovery and divided it into several empirical, albeit very general, inquiries. Of these, phaneroscopy (phenomenology) is the most basic. Phaneroscopy depends not only on empiricism’s expansion (Chapter 7) but also on a vocabulary of phaneroscopic description, free of metaphysical assumptions, drawn from the algebra of relations. The resulting three phaneroscopic categories are here developed systematically. Peirce’s 1903 reformulation of pragmatism (Chapter 4) mandated a phaneroscopic account of the meaning of modal and metaphysical ideas – of possibility, actuality, and, especially, law – by which to establish the meaningfulness of modal realism. This implies that some forms of lawfulness are directly perceived. But direct (i.e., non-inferential) perception of lawfulness does not prove law’s reality, which must remain a hypothesis supported, never proven, by common experience and especially by the progress of scientific inquiry.

This chapter examines what was most constant in Peirce’s thought albeit constantly developing. He was always an idealist but not always in the same way. His early embrace of scholastic realism deepened over time so as to include triadic relations and the recognition that these entail modal realism. Modal realism affirms the irreducible meaningfulness of subjunctive conditionals, hence, the reality of what would be and what would have been. In his initial 1878 statement of what came to be called ’the pragmatic maxim’ (not a theory of meaning but a prescription for growth in meaning, that is, ’clarification’), Peirce explicitly denied modal realism. But that maxim requires the meaningfulness of modal locutions, for which nonetheless it cannot account. The resulting problems (e.g., that of ’buried secrets’) were resolved in 1903 by a revised maxim that added a Lockean dimension of meaning to the pragmatic dimension – an addition not heretofore recognized.

This chapter defends Peirce’s conception of science against a pair of current, mutually antagonistic ideas of the difference of modern science from classical and medieval philosophy. The one party celebrates the difference, the other deplores it, but they agree that modern science rejects the classical ideal of theory as knowledge good for itself. Peirce saw that difference more subtly as one in which the classical ideal of knowing is transformed rather than abandoned. This revolution in cognitive aim did not occur arbitrarily. Well-established facts about the defeat of the Aristotelian world-view are cited to support the novel thesis that it depended on an empirical yet normative discovery, that restless, unending, specialist inquiry is more satisfying intellectually than is the dialectic of systems. The history of science reviewed in this chapter provides evidence for the argument of Chapter 9, that there is normative knowledge and that it is empirical.