On this erroneous objective use of the Ideas three so-called sciences are based:  speculative psychology, speculative cosmology, and speculative theology, which, together with ontology, constitute the stately structure of the (Wolffian) metaphysics.  The Critique of Reason completes its work of destruction when, as Dialectic (Logic cf.  Illusion), it follows the refutation of dogmatic ontology—­developed in the Analytic—­which believed that it knew things in themselves through the concepts of the understanding, with a refutation of rational psychology, rational cosmology, and rational theology.  It shows that the first is founded on paralogisms, and the second entangled in irreconcilable contradictions, while the third makes vain efforts to prove the existence of the Supreme Being.

(i) The Paralogisms of Rational Psychology.  The transcendental self-consciousness or pure ego which accompanies and connects all my representations, the subject of all judgments which I form, is, as the Analytic recognized, the presupposition of all knowing (pp. 358-359), but as such it can never become an object of knowledge.  We must not make a given object out of the subject which never can be a predicate, nor substitute a real thinking substance for the logical subject of thought, nor revamp the unity of self-consciousness into the simplicity and identical personality of the soul.  The rational psychology of the Wolffian school is guilty of this error, and whatever of proof it advances for the substantiality, simplicity, and personality of the soul, and, by way of deduction, for its immateriality and immortality as well as for its relation to the body, is based upon this substitution, this ambiguity of the middle term, and therefore upon a quaternio terminorum,—­all its conclusions are fallacious.  It is allowable and unavoidable to add in thought an absolute subject, the unity of the ego, to inner phenomena;[1] it is inadmissible to treat the Idea of the soul as a knowable thing.  In order to be able to apply the category of substance to it, we would have to lay hold of a permanent in intuition such as cannot be found in the inner sense.  Empirical psychology, then, alone remains for the extension of our knowledge of mental life, while rational psychology shrivels up from a doctrine into a mere discipline, which watches that the limits of experience are not overstepped.  But even as a mere limiting determination it has great value.  For, along with the hope of proving the immateriality and immortality of the soul, the fear of seeing them disproved is also dissipated; materialism is just as unfounded as spiritualism, and if the conclusions of the latter concerning the soul as a simple, immaterial substance which survives the death of the body, cannot be proved, yet we need not, for that reason, regard them as erroneous, for the opposite is as little susceptible of demonstration.  The whole question belongs not in the forum of knowledge, but in the forum of faith, and that which we gain by the proof that nothing can be determined concerning it by theoretical reasoning (viz., assurance against materialistic objections) is far more valuable than what we lose.