Reason, as the faculty of principles, determines the interest of all the powers of the mind and is determined by its own.The interest of its speculative employment consists in the cognition of the object pushed to the highest a priori principles: that of its practical employment, in the determination of the will in respect of the final and complete end.As to what is necessary for the possibility of any employment of reason at all, namely, that its principles and affirmations should not contradict one another, this constitutes no part of its interest, but is the condition of having reason at all; it is only its development, not mere consistency with itself, that is reckoned as its interest.
If practical reason could not assume or think as given anything further than what speculative reason of itself could offer it from its own insight, the latter would have the primacy.But supposing that it had of itself original a priori principles with which certain theoretical positions were inseparably connected, while these were withdrawn from any possible insight of speculative reason (which, however, they must not contradict); then the question is: Which interest is the superior (not which must give way, for they are not necessarily conflicting), whether speculative reason, which knows nothing of all that the practical offers for its acceptance, should take up these propositions and (although they transcend it) try to unite them with its own concepts as a foreign possession handed over to it, or whether it is justified in obstinately following its own separate interest and, according to the canonic of Epicurus, rejecting as vain subtlety everything that cannot accredit its objective reality by manifest examples to be shown in experience, even though it should be never so much interwoven with the interest of the practical (pure) use of reason, and in itself not contradictory to the theoretical, merely because it infringes on the interest of the speculative reason to this extent, that it removes the bounds which this latter had set to itself, and gives it up to every nonsense or delusion of imagination?
In fact, so far as practical reason is taken as dependent on pathological conditions, that is, as merely regulating the inclinations under the sensible principle of happiness, we could not require speculative reason to take its principles from such a source.Mohammed's paradise, or the absorption into the Deity of the theosophists and mystics would press their monstrosities on the reason according to the taste of each, and one might as well have no reason as surrender it in such fashion to all sorts of dreams.But if pure reason of itself can be practical and is actually so, as the consciousness of the moral law proves, then it is still only one and the same reason which, whether in a theoretical or a practical point of view, judges according to a priori principles; and then it is clear that although it is in the first point of view incompetent to establish certain propositions positively, which, however, do not contradict it, then, as soon as these propositions are inseparably attached to the practical interest of pure reason, it must accept them, though it be as something offered to it from a foreign source, something that has not grown on its own ground, but yet is sufficiently authenticated; and it must try to compare and connect them with everything that it has in its power as speculative reason.
It must remember, however, that these are not additions to its insight, but yet are extensions of its employment in another, namely, a practical aspect; and this is not in the least opposed to its interest, which consists in the restriction of wild speculation.
Thus, when pure speculative and pure practical reason are combined in one cognition, the latter has the primacy, provided, namely, that this combination is not contingent and arbitrary, but founded a priori on reason itself and therefore necessary.For without this subordination there would arise a conflict of reason with itself;since, if they were merely co-ordinate, the former would close its boundaries strictly and admit nothing from the latter into its domain, while the latter would extend its bounds over everything and when its needs required would seek to embrace the former within them.Nor could we reverse the order and require pure practical reason to be subordinate to the speculative, since all interest is ultimately practical, and even that of speculative reason is conditional, and it is only in the practical employment of reason that it is complete.
IV.The Immortality of the Soul as a Postulate of Pure Practical Reason.
The realization of the summum bonum in the world is the necessary object of a will determinable by the moral law.But in this will the perfect accordance of the mind with the moral law is the supreme condition of the summum bonum.This then must be possible, as well as its object, since it is contained in the command to promote the latter.Now, the perfect accordance of the will with the moral law is holiness, a perfection of which no rational being of the sensible world is capable at any moment of his existence.Since, nevertheless, it is required as practically necessary, it can only be found in a progress in infinitum towards that perfect accordance, and on the principles of pure practical reason it is necessary to assume such a practical progress as the real object of our will.
