This duty is founded on something that is indeed quite independent of these suppositions and is of itself apodeictically certain, namely, the moral law; and so far it needs no further support by theoretical views as to the inner constitution of things, the secret final aim of the order of the world, or a presiding ruler thereof, in order to bind me in the most perfect manner to act in unconditional conformity to the law.But the subjective effect of this law, namely, the mental disposition conformed to it and made necessary by it, to promote the practically possible summum bonum, this pre-supposes at least that the latter is possible, for it would be practically impossible to strive after the object of a conception which at bottom was empty and had no object.Now the above-mentioned postulates concern only the physical or metaphysical conditions of the possibility of the summum bonum; in a word, those which lie in the nature of things; not, however, for the sake of an arbitrary speculative purpose, but of a practically necessary end of a pure rational will, which in this case does not choose, but obeys an inexorable command of reason, the foundation of which is objective, in the constitution of things as they must be universally judged by pure reason, and is not based on inclination; for we are in nowise justified in assuming, on account of what we wish on merely subjective grounds, that the means thereto are possible or that its object is real.This, then, is an absolutely necessary requirement, and what it pre-supposes is not merely justified as an allowable hypothesis, but as a postulate in a practical point of view; and admitting that the pure moral law inexorably binds every man as a command (not as a rule of prudence), the righteous man may say: "I will that there be a God, that my existence in this world be also an existence outside the chain of physical causes and in a pure world of the understanding, and lastly, that my duration be endless; I firmly abide by this, and will not let this faith be taken from me; for in this instance alone my interest, because I must not relax anything of it, inevitably determines my judgement, without regarding sophistries, however unable I may be to answer them or to oppose them with others more plausible.*[2]
*But even here we should not be able to allege a requirement of reason, if we had not before our eyes a problematical, but yet inevitable, conception of reason, namely, that of an absolutely necessary being.This conception now seeks to be defined, and this, in addition to the tendency to extend itself, is the objective ground of a requirement of speculative reason, namely, to have a more precise definition of the conception of a necessary being which is to serve as the first cause of other beings, so as to make these latter knowable by some means.Without such antecedent necessary problems there are no requirements- at least not of pure reason- the rest are requirements of inclination.
*[2] In the Deutsches Museum, February, 1787, there is a dissertation by a very subtle and clear-headed man, the late Wizenmann, whose early death is to be lamented, in which he disputes the right to argue from a want to the objective reality of its object, and illustrates the point by the example of a man in love, who having fooled himself into an idea of beauty, which is merely a chimera of his own brain, would fain conclude that such an object really exists somewhere.I quite agree with him in this, in all cases where the want is founded on inclination, which cannot necessarily postulate the existence of its object even for the man that is affected by it, much less can it contain a demand valid for everyone, and therefore it is merely a subjective ground of the wish.But in the present case we have a want of reason springing from an objective determining principle of the will, namely, the moral law, which necessarily binds every rational being, and therefore justifies him in assuming a priori in nature the conditions proper for it, and makes the latter inseparable from the complete practical use of reason.It is a duty to realize the summum bonum to the utmost of our power, therefore it must be possible, consequently it is unavoidable for every rational being in the world to assume what is necessary for its objective possibility.The assumption is as necessary as the moral law, in connection with which alone it is valid.
In order to prevent misconception in the use of a notion as yet so unusual as that of a faith of pure practical reason, let me be permitted to add one more remark.It might almost seem as if this rational faith were here announced as itself a command, namely, that we should assume the summum bonum as possible.But a faith that is commanded is nonsense.Let the preceding analysis, however, be remembered of what is required to be supposed in the conception of the summum bonum, and it will be seen that it cannot be commanded to assume this possibility, and no practical disposition of mind is required to admit it; but that speculative reason must concede it without being asked, for no one can affirm that it is impossible in itself that rational beings in the world should at the same time be worthy of happiness in conformity with the moral law and also possess this happiness proportionately.Now in respect of the first element of the summum bonum, namely, that which concerns morality, the moral law gives merely a command, and to doubt the possibility of that element would be the same as to call in question the moral law itself.