There exists in the faculty of reason a natural desire to venture beyond the field of experience, to attempt to reach the utmost bounds of all cognition by the help of ideas alone, and not to rest satisfied until it has fulfilled its course and raised the sum of its cognitions into a self-subsistent systematic whole. Is the motive for this endeavour to be found in its speculative, or in its practical interests alone?
Setting aside, at present, the results of the labours of pure reason in its speculative exercise, I shall merely inquire regarding the problems the solution of which forms its ultimate aim, whether reached or not, and in relation to which all other aims are but partial and intermediate. These highest aims must, from the nature of reason, possess complete unity; otherwise the highest interest of humanity could not be successfully promoted.
The transcendental speculation of reason relates to three things: the freedom of the will, the immortality of the soul, and the existence of God. The speculative interest which reason has in those questions is very small; and, for its sake alone, we should not undertake the labour of transcendental investigation- a labour full of toil and ceaseless struggle. We should be loth to undertake this labour, because the discoveries we might make would not be of the smallest use in the sphere of concrete or physical investigation. We may find out that the will is free, but this knowledge only relates to the intelligible cause of our volition. As regards the phenomena or expressions of this will, that is, our actions, we are bound, in obedience to an inviolable maxim, without which reason cannot be employed in the sphere of experience, to explain these in the same way as we explain all the other phenomena of nature, that is to say, according to its unchangeable laws. We may have discovered the spirituality and immortality of the soul, but we cannot employ this knowledge to explain the phenomena of this life, nor the peculiar nature of the future, because our conception of an incorporeal nature is purely negative and does not add anything to our knowledge, and the only inferences to be drawn from it are purely fictitious. If, again, we prove the existence of a supreme intelligence, we should be able from it to make the conformity to aims existing in the arrangement of the world comprehensible; but we should not be justified in deducing from it any particular arrangement or disposition, or inferring any where it is not perceived. For it is a necessary rule of the speculative use of reason that we must not overlook natural causes, or refuse to listen to the teaching of experience, for the sake of deducing what we know and perceive from something that transcends all our knowledge. In one word, these three propositions are, for the speculative reason, always transcendent, and cannot be employed as immanent principles in relation to the objects of experience; they are, consequently, of no use to us in this sphere, being but the valueless results of the severe but unprofitable efforts of reason.
If, then, the actual cognition of these three cardinal propositions is perfectly useless, while Reason uses her utmost endeavours to induce us to admit them, it is plain that their real value and importance relate to our practical, and not to our speculative interest.
I term all that is possible through free will, practical. But if the conditions of the exercise of free volition are empirical, reason can have only a regulative, and not a constitutive, influence upon it, and is serviceable merely for the introduction of unity into its empirical laws. In the moral philosophy of prudence, for example, the sole business of reason is to bring about a union of all the ends, which are aimed at by our inclinations, into one ultimate end- that of happiness- and to show the agreement which should exist among the means of attaining that end. In this sphere, accordingly, reason cannot present to us any other than pragmatical laws of free action, for our guidance towards the aims set up by the senses, and is incompetent to give us laws which are pure and determined completely a priori. On the other hand, pure practical laws, the ends of which have been given by reason entirely a priori, and which are not empirically conditioned, but are, on the contrary, absolutely imperative in their nature, would be products of pure reason. Such are the moral laws; and these alone belong to the sphere of the practical exercise of reason, and admit of a canon.
All the powers of reason, in the sphere of what may be termed pure philosophy, are, in fact, directed to the three above-mentioned problems alone. These again have a still higher end- the answer to the question, what we ought to do, if the will is free, if there is a God and a future world. Now, as this problem relates to our in reference to the highest aim of humanity, it is evident that the ultimate intention of nature, in the constitution of our reason, has been directed to the moral alone.
We must take care, however, in turning our attention to an object which is foreign* to the sphere of transcendental philosophy, not to injure the unity of our system by digressions, nor, on the other hand, to fail in clearness, by saying too little on the new subject of discussion. I hope to avoid both extremes, by keeping as close as possible to the transcendental, and excluding all psychological, that is, empirical, elements.
*All practical conceptions relate to objects of pleasure and pain, and consequently- in an indirect manner, at least- to objects of feeling. But as feeling is not a faculty of representation, but lies out of the sphere of our powers of cognition, the elements of our judgements, in so far as they relate to pleasure or pain, that is, the elements of our practical judgements, do not belong to transcendental philosophy, which has to do with pure a priori cognitions alone.
I have to remark, in the first place, that at present I treat of the conception of freedom in the practical sense only, and set aside the corresponding transcendental conception, which cannot be employed as a ground of explanation in the phenomenal world, but is itself a problem for pure reason. A will is purely animal (arbitrium brutum) when it is determined by sensuous impulses or instincts only, that is, when it is determined in a pathological manner. A will, which can be determined independently of sensuous impulses, consequently by motives presented by reason alone, is called a free will (arbitrium liberum); and everything which is connected with this free will, either as principle or consequence, is termed practical. The existence of practical freedom can be proved from experience alone. For the human will is not determined by that alone which immediately affects the senses; on the contrary, we have the power, by calling up the notion of what is useful or hurtful in a more distant relation, of overcoming the immediate impressions on our sensuous faculty of desire. But these considerations of what is desirable in relation to our whole state, that is, is in the end good and useful, are based entirely upon reason. This faculty, accordingly, enounces laws, which are imperative or objective laws of freedom and which tell us what ought to take place, thus distinguishing themselves from the laws of nature, which relate to that which does take place. The laws of freedom or of free will are hence termed practical laws.
Whether reason is not itself, in the actual delivery of these laws, determined in its turn by other influences, and whether the action which, in relation to sensuous impulses, we call free, may not, in relation to higher and more remote operative causes, really form a part of nature- these are questions which do not here concern us. They are purely speculative questions; and all we have to do, in the practical sphere, is to inquire into the rule of conduct which reason has to present. Experience demonstrates to us the existence of practical freedom as one of the causes which exist in nature, that is, it shows the causal power of reason in the determination of the will. The idea of transcendental freedom, on the contrary, requires that reason- in relation to its causal power of commencing a series of phenomena- should be independent of all sensuous determining causes; and thus it seems to be in opposition to the law of nature and to all possible experience. It therefore remains a problem for the human mind. But this problem does not concern reason in its practical use; and we have, therefore, in a canon of pure reason, to do with only two questions, which relate to the practical interest of pure reason: Is there a God? and, Is there a future life? The question of transcendental freedom is purely speculative, and we may therefore set it entirely aside when we come to treat of practical reason. Besides, we have already discussed this subject in the antinomy of pure reason.