Now, this endless progress is only possible on the supposition of an endless duration of the existence and personality of the same rational being (which is called the immortality of the soul).The summum bonum, then, practically is only possible on the supposition of the immortality of the soul; consequently this immortality, being inseparably connected with the moral law, is a postulate of pure practical reason (by which I mean a theoretical proposition, not demonstrable as such, but which is an inseparable result of an unconditional a priori practical law.
This principle of the moral destination of our nature, namely, that it is only in an endless progress that we can attain perfect accordance with the moral law, is of the greatest use, not merely for the present purpose of supplementing the impotence of speculative reason, but also with respect to religion.In default of it, either the moral law is quite degraded from its holiness, being made out to be indulgent and conformable to our convenience, or else men strain their notions of their vocation and their expectation to an unattainable goal, hoping to acquire complete holiness of will, and so they lose themselves in fanatical theosophic dreams, which wholly contradict self-knowledge.In both cases the unceasing effort to obey punctually and thoroughly a strict and inflexible command of reason, which yet is not ideal but real, is only hindered.For a rational but finite being, the only thing possible is an endless progress from the lower to higher degrees of moral perfection.The Infinite Being, to whom the condition of time is nothing, sees in this to us endless succession a whole of accordance with the moral law; and the holiness which his command inexorably requires, in order to be true to his justice in the share which He assigns to each in the summum bonum, is to be found in a single intellectual intuition of the whole existence of rational beings.All that can be expected of the creature in respect of the hope of this participation would be the consciousness of his tried character, by which from the progress he has hitherto made from the worse to the morally better, and the immutability of purpose which has thus become known to him, he may hope for a further unbroken continuance of the same, however long his existence may last, even beyond this life,* and thus he may hope, not indeed here, nor in any imaginable point of his future existence, but only in the endlessness of his duration (which God alone can survey) to be perfectly adequate to his will (without indulgence or excuse, which do not harmonize with justice).
*It seems, nevertheless, impossible for a creature to have the conviction of his unwavering firmness of mind in the progress towards goodness.On this account the Christian religion makes it come only from the same Spirit that works sanctification, that is, this firm purpose, and with it the consciousness of steadfastness in the moral progress.But naturally one who is conscious that he has persevered through a long portion of his life up to the end in the progress to the better, and this genuine moral motives, may well have the comforting hope, though not the certainty, that even in an existence prolonged beyond this life he will continue in these principles; and although he is never justified here in his own eyes, nor can ever hope to be so in the increased perfection of his nature, to which he looks forward, together with an increase of duties, nevertheless in this progress which, though it is directed to a goal infinitely remote, yet is in God's sight regarded as equivalent to possession, he may have a prospect of a blessed future; for this is the word that reason employs to designate perfect well-being independent of all contingent causes of the world, and which, like holiness, is an idea that can be contained only in an endless progress and its totality, and consequently is never fully attained by a creature.
V.The Existence of God as a Postulate of Pure Practical Reason.
In the foregoing analysis the moral law led to a practical problem which is prescribed by pure reason alone, without the aid of any sensible motives, namely, that of the necessary completeness of the first and principle element of the summum bonum, viz., morality;and, as this can be perfectly solved only in eternity, to the postulate of immortality.The same law must also lead us to affirm the possibility of the second element of the summum bonum, viz., happiness proportioned to that morality, and this on grounds as disinterested as before, and solely from impartial reason; that is, it must lead to the supposition of the existence of a cause adequate to this effect; in other words, it must postulate the existence of God, as the necessary condition of the possibility of the summum bonum (an object of the will which is necessarily connected with the moral legislation of pure reason).We proceed to exhibit this connection in a convincing manner.
Happiness is the condition of a rational being in the world with whom everything goes according to his wish and will; it rests, therefore, on the harmony of physical nature with his whole end and likewise with the essential determining principle of his will.Now the moral law as a law of ******* commands by determining principles, which ought to be quite independent of nature and of its harmony with our faculty of desire (as springs).But the acting rational being in the world is not the cause of the world and of nature itself.There is not the least ground, therefore, in the moral law for a necessary connection between morality and proportionate happiness in a being that belongs to the world as part of it, and therefore dependent on it, and which for that reason cannot by his will be a cause of this nature, nor by his own power make it thoroughly harmonize, as far as his happiness is concerned, with his practical principles.