Introduction

The theoretical use of reason was concerned with objects of the cognitive faculty only, and a critical examination of it with reference to this use applied properly only to the pure faculty of cognition; because this raised the suspicion, which was afterwards confirmed, that it might easily pass beyond its limits, and be lost among unattainable objects, or even contradictory notions. It is quite different with the practical use of reason. In this, reason is concerned with the grounds of determination of the will, which is a faculty either to produce objects corresponding to ideas, or to determine ourselves to the effecting of such objects (whether the physical power is sufficient or not); that is, to determine our causality. For here, reason can at least attain so far as to determine the will, and has always objective reality in so far as it is the volition only that is in question. The first question here then is whether pure reason of itself alone suffices to determine the will, or whether it can be a ground of determination only as dependent on empirical conditions. Now, here there comes in a notion of causality justified by the critique of the pure reason, although not capable of being presented empirically, viz., that of freedom; and if we can now discover means of proving that this property does in fact belong to the human will (and so to the will of all rational beings), then it will not only be shown that pure reason can be practical, but that it alone, and not reason empirically limited, is indubitably practical; consequently, we shall have to make a critical examination, not of pure practical reason, but only of practical reason generally. For when once pure reason is shown to exist, it needs no critical examination. For reason itself contains the standard for the critical examination of every use of it. The critique, then, of practical reason generally is bound to prevent the empirically conditioned reason from claiming exclusively to furnish the ground of determination of the will. If it is proved that there is a [practical] reason, its employment is alone immanent; the empirically conditioned use, which claims supremacy, is on the contrary transcendent and expresses itself in demands and precepts which go quite beyond its sphere. This is just the opposite of what might be said of pure reason in its speculative employment.

The theoretical use of reason concerned only the objects of our capacity for knowledge. A critical examination of reason in this use therefore properly applied only to the pure capacity for knowledge. This was because there was reason to suspect that it could easily go beyond its limits. It might then lose itself among objects beyond its reach, or even among contradictory ideas. This suspicion was later confirmed. The practical use of reason is quite different. Here, reason is concerned with what determines the will. The will is a capacity either to produce objects corresponding to ideas or to commit ourselves to producing them. This is so whether or not we have the physical power to produce them. In other words, the will determines our power to bring about effects. Here, reason can at least succeed in determining the will. As far as willing alone is concerned, reason always has objective reality. The first question, then, is whether pure reason alone is enough to determine the will. Or can reason determine the will only when it depends on conditions drawn from experience? Here, a concept of causality enters the discussion. This concept is freedom. The critique of pure reason justified it, although it cannot be demonstrated through experience. Now suppose we can find a way to prove that freedom does belong to the human will, and therefore to the will of all rational beings. This would show not only that pure reason can be practical. It would also show that pure reason alone, and not reason limited by experience, is undoubtedly practical. Consequently, we must critically examine practical reason in general, not pure practical reason. Once pure reason is shown to exist, it needs no critical examination. Reason itself contains the standard for critically examining every use of reason. The critique of practical reason in general must therefore prevent reason conditioned by experience from claiming that it alone can determine the will. If a [practical] reason is proved to exist, its use alone is immanent, or within its proper limits. By contrast, the use of reason conditioned by experience is transcendent when it claims supremacy. It then expresses itself in demands and rules that go far beyond its proper sphere. This is just the opposite of what might be said of pure reason in its speculative use.

However, as it is still pure reason, the knowledge of which is here the foundation of its practical employment, the general outline of the classification of a critique of practical reason must be arranged in accordance with that of the speculative. We must, then, have the Elements and the Methodology of it; and in the former an Analytic as the rule of truth, and a Dialectic as the exposition and dissolution of the illusion in the judgements of practical reason. But the order in the subdivision of the Analytic will be the reverse of that in the critique of the pure speculative reason. For, in the present case, we shall commence with the principles and proceed to the concepts, and only then, if possible, to the senses; whereas in the case of the speculative reason we began with the senses and had to end with the principles. The reason of this lies again in this: that now we have to do with a will, and have to consider reason, not in its relation to objects, but to this will and its causality. We must, then, begin with the principles of a causality not empirically conditioned, after which the attempt can be made to establish our notions of the determining grounds of such a will, of their application to objects, and finally to the subject and its sense faculty. We necessarily begin with the law of causality from freedom, that is, with a pure practical principle, and this determines the objects to which alone it can be applied.

However, this is still pure reason, and knowledge of pure reason is the basis for its practical use. So the general structure of a critique of practical reason must follow that of the critique of speculative reason. It must have an Elements section and a Methodology section. The Elements must include an Analytic as the rule of truth. They must also include a Dialectic to explain and dispel the illusion in judgments of practical reason. But the subdivisions of the Analytic will follow the reverse order from those in the critique of pure speculative reason. Here, we will begin with principles, proceed to concepts, and only then, if possible, turn to the senses. In the critique of speculative reason, by contrast, we began with the senses and had to end with principles. Again, the reason for this difference is that we are now concerned with a will. We must consider reason not in relation to objects, but in relation to the will and its causality. So we must begin with the principles of a causality that is not conditioned by experience. After that, we can try to establish our concepts of what determines such a will. We can then consider how these concepts apply to objects, and finally to the subject and its capacity for sensation. We must begin with the law of causality from freedom, that is, with a pure practical principle. This principle determines the only objects to which it can be applied.