3. Still, if the human knowledge makes no effort to stride beyond the narrow limits of experience, _i. e._ to become transcendent, it involves itself in the greatest contradictions. The three ideas of the reason, the psychological, the cosmological, and the theological, viz. (_a_) the idea of an absolute subject, _i. e._ of the soul, or of immortality, (_b_) the idea of the world as a totality of all conditions and phenomena, (_c_) the idea of a most perfect being—are so wholly without application to the empirical actuality, are so truly regulative, and not constitutive principles, which are only the pure products of the reason, and are so entirely without a correspondent object in experience, that whenever they are applied to experience, _i. e._ become conceived of as actually existing objects, they lead to pure logical errors, to the most obvious paralogisms and sophisms. These errors, which are partly false conclusions and paralogisms, and partly unavoidable contradictions of the reason with itself, Kant undertook to show in reference to all the ideas of the reason. Take, _e. g._ the cosmological idea. Whenever the reason posits any transcendental expressions in reference to the universe, _i. e._ attempts to apply the forms of the finite to the infinite, it is at once evident that the antithesis of those expressions can be proved just as well as the thesis. The affirmation that the world has a beginning in time, and limits in space, can be proved as well as, and no better than its opposite, that the world has no beginning in time, and no spacial limits. Whence it follows that all speculative cosmology is an assumption by the reason. So also with the theological idea; it rests on bare logical paralogisms, and false conclusions, as Kant, with great acuteness, shows in reference to each of the proofs for the being of a God, which previous dogmatic philosophies had attempted. It is therefore impossible to prove and to conceive of the existence of a God as a Supreme Being, or of the soul as a real subject, or of a comprehending universe. The peculiar problems of metaphysics lie outside the province of philosophical knowledge.
Such is the negative part of the Kantian philosophy; its positive complement is found in the “_Critick of the Practical Reason_.” While the mind as theoretical and cognitive is wholly conditioned, and ruled by the objective and sensible world, and thus knowledge is only possible through intuition, yet as practical does it go wholly beyond the given (the sense impulse), and is determined only through the categorical imperative, and the moral law, which is itself, and is therefore free and autonomic; the ends which it pursues are those which itself, as moral spirit, places before itself; objects are no more its masters and lawgivers, to which it must yield if it would know the truth, but its servants, which it may use for its own ends in actualizing its moral law. While the theoretical mind is united to a world of sense and phenomena, a world obedient to necessary laws, the practical mind, by virtue of the freedom essential to it, by virtue of its direction towards an absolute aim, belongs to a purely intelligible and supersensible world. This is the practical idealism of Kant, from which he derives the three practical postulates of the immortality of the soul, moral freedom, and the being of a God, which, as theoretical truths, had been before denied.