This chapter examines Charles Peirce's remark. Peirce and Kant are both cognitive constructivists. From his constructivist perspective Kant favors an a priori conception of cognition, whereas Peirce embraces an a posteriori approach. Peirce pragmatism is a different form of the pragmatism he attributes to the critical philosophy. The chapter explains the distinction between the Peircean and the Kantian normative conceptions of cognition in respect to the latter's moral theory. Kant bases his deontological theory of morality on his understanding of an "imperative" or, roughly, a requirement of reason. Peirce bases his use of the term "pragmatism" on his reading of Kant. Peirce distinguishes between real doubt and theoretical doubt, which afflicts only philosophers concerned with overcoming difficulties raised by other philosophers as opposed to those raised in real life. Kant applies his a priori approach to cognition to modern natural science. He was very familiar with and made a number of important contributions to modern natural science, especially astrophysics.