The great majority of philosophers and theologians still hold the contrary opinion. They affirm, with Kant, that the moral world is quite independent of the physical, and is subject to very different laws; hence a man's conscience, as the basis of his moral life, must also be quite independent of our scientific knowledge of the world, and must be based rather on his religious faith. On that theory the study of the moral world belongs to _practical_ reason, while that of nature, or of the physical world, is referred to _pure_ or theoretical reason. This unequivocal and conscious dualism of Kant's philosophy was its greatest defect; it has caused, and still causes, incalculable mischief. First of all the "critical Kant" had built up the splendid and marvellous palace of pure reason, and convincingly proved that the three great central dogmas of metaphysics--a personal God, free will, and the immortal soul--had no place whatever in it, and that no rational proof could be found of their reality. Afterwards, however, the "dogmatic Kant" superimposed on this true crystal palace of _pure_ reason the glittering, ideal castle in the air of _practical_ reason, in which three imposing church-naves were designed for the accommodation of those three great mystic divinities. When they had been put out at the front door by rational knowledge they returned by the back door under the guidance of irrational faith. The cupola of his great cathedral of faith was crowned by Kant with his curious idol, the famous "categorical imperative." According to it, the demand of the universal moral law is unconditional, independent of any regard to actuality or potentiality. It runs: "Act at all times in such wise that the maxim (or the subjective law of thy will) may hold good as a principle of a universal law." On that theory all normal men would have the same sense of duty. Modern anthropology has ruthlessly dissipated that pretty dream; it has shown that conceptions of duty differ even more among uncivilized than among civilized nations. All the actions and customs which we regard as sins or loathsome crimes (theft, fraud, murder, adultery, etc.) are considered by other nations in certain circumstances to be virtues, or even sacred duties.