His philosophical writings include: "Inductive Logic" (1896); "The Problems of Philosophy" (1898); "Hegel's Logic" (1902); "Deductive and Inductive Logic" (1905). All of these show mathematical precision of statement and lucid exposition. His books on logic, though later superseded, still constituted a valuable approach to the Hegelian system. His most enduring contribution is "The Philosophy of the Enlightenment" (1910) in the Epochs of Philosophy Series, of which he was the general editor. His account of the development of Kant's philosophy is masterly, and he ranks Kant as the culminating thinker of the Enlightenment. The Kantian emphasis on moral freedom through intuitive recognition and willing assent to a universally binding moral law was the keynote of his ethics and the fulcrum of his opposition to all forms of utilitarianism and pragmatism. In "The Vocation of the Scholar," in the volume "A Defense of Prejudice," he opposes William James's "creed of change," with this declaration of philosophical fundamentalism: "There are certain ideas which in the history of the race experience have become established for all time, for all places, and for all persons and things" (pp. 146–47).