In his Critique of Judgment Kant seeks to deal with the person who is unable to believe in the existence of a God or a soul. This atheist is required by the moral law to continue his moral acts and not to deviate from that law. But on a practical basis this is hardly to be expected and even at best his moral fervor would greatly diminish and even vanish. If an atheist wants to remain strong in his moral commitment and yet cannot, due to the inanity of the purpose asserted for the moral act, i.e., the Highest Good (where moral perfection is matched by commensurate happiness), then Kant calls for him simply to assume the existence of God and act accordingly. There is no contradiction for him doing this, for here the question is not concerned with theory and speculation, but merely with practice.

7.1 This proof, which can be expressed with logical precision, does not claim to say that: “it is just as necessary to assume the existence of God as to acknowledge the validity of the moral law”; and thus also not: “who cannot persuade himself of the former may judge himself to be released from the obligation of the latter”.

7.2 Not at all! Only the aiming at the final purpose in the world, operating through the compliance of the latter (as happiness of rational beings harmoniously commensurate with the compliance with moral laws, as the highest world best) would then have to be given up.

7.3 Every rational person would still always have to recognize himself as strictly bound to the prescriptions of morality, for those laws are formal and are commanded unconditionally and without regard to purposes (where purposes are the material of the wanting).

7.4 But that one requirement of the final purpose, as practical reason prescribes it to the beings of a world, is a purpose which is undeniably required via man's nature (as a finite entity). And reason claims to know this natural demand as subject only to the moral law as the inviolable condition (or also made universal according to that) and so makes the promotion of happiness in agreement with morality to be the final purpose.

7.5 Now to promote this final purpose as much (concerning happiness and morality) as is in our capacity, is commanded through the moral law; and letting the turn of events, which this striving may obtain, be what it will.*

7.6 The fulfillment of duty consists in the form of the sincere will, not in the mediating causes of the success.

[* And so we are morally required to pursue the highest good even though we could have no guarantee that its natural and rational final purpose will be attained.]

8.1 Assume therefore, that someone is moved partly by the weakness of all the exalted speculative arguments, and partly through some irregularities appearing to him in nature and the moral world and comes to the persuasion that there is no God. But still even in his own eyes he would be an unworthy person if he, for that reason, were to hold the laws of duty as merely imagined, invalid and nonbinding and to resolve boldly to overstep them.

8.2 If such a person could subsequently convince himself of the existence of God and overcome these doubts and were even quite exact in the performance of his morally required duty, he would still be an unworthy person in thinking about morally in that way and such that his compliance were based on fear or in anticipation of some reward and so where his disposition were not duty for the sake of duty.

8.3 On the other hand, let this person continue to comply properly and selflessly as a believer according to his consciousness and then as a thought-trial let him assume there were no God. If he were then to consider himself free of all moral obligation, we would have to judge that his internal moral disposition were not rightly ordered within him.*

[* Strictly speaking Kant is correct here. However it is still true that most theists, upon becoming convinced that there were no God, i.e., becoming atheists, would find that the moral law along with everything else in existence were utterly inane and pointless. Accordingly there would be a natural tilt toward nihilism and a universal emptiness and absurdity. And they would hardly be concerned about any judgment of their internal moral disposition. There would be a natural (but still not insurmountable) temptation to disregard the moral law. See comment to 10.5 below.]

9.1 Therefore let us assume a righteous man (e.g., Spinoza) who is firmly persuaded that there is no God and also no future life (because with respect to the object of morality the absence of any God has the same effect as no future life). How will such a man assess his own internal determination of purpose through the moral law which he actively honors?

9.2 He requires no advantage for himself from compliance with that [moral law] either in this world or in any other. Instead he will unselfishly promote only the good to which that holy law directs all his powers.

9.3 But his effort [in pursuit of that good] is limited.* Occasionally he can expect a chance cooperation from nature, but never any correspondence with his purpose according to regular and enduring rules (as inwardly his maxims are and must be) and which purpose he still feels himself bound and impelled to produce.

9.4 Deceit, violence and envy will always sway about him even though he is upright, peaceful and well-meaning. And the upright people whom he encounters apart from himself, regardless of all their worthiness for happiness, will still be subjected by nature (which pays no attention to such worthiness) to all the evils of deprivation, sickness and untimely death that greet the other animals of the earth. And this will always be the case until a wide grave swallows them all together (upright or not--for here that makes no difference), and casts those who were able to believe in a final purpose of the creation back into the abyss of the purposeless chaos of matter from which they had been drawn.

9.5 In any case, therefore, this well-disposed atheist would have to give up as impossible the purpose which he had in mind, and should have in mind, regarding compliance with the moral law. But if he wants to remain devoted to the call of his moral, internal determination and not to weaken the respect (which moves him directly to obey the moral law) by means of the inanity of the single, ideal, final purpose commensurate with its higher demand--and this [weakening] cannot occur without injury to the moral disposition--then in the practical intention (which he also can very easily do, since at least it is not contradictory per se to make a concept of at least the possibility of the final purpose which morality prescribed to him), he must assume the existence of a moral author of the world, i.e., God.**

[* He will be promoting as much goodness as he can, but will often find nothing good ensuing from his efforts.]

[** Here Kant tells us that without the Highest Good as the final purpose of the moral act, the respect for the moral law will likely weaken, and this can only be avoided by simply deciding that there is a God, i.e., by assuming a God and acting on that assumption. This is consistent with Kant's thinking in his Religion Within The Bounds Of Sheer Reason where it is not to be expected for an individual to maintain moral fervor in this evil world and where the only hope for moral improvement is in cooperation with others of a like spirit in a church (and which calls for God).]

Note: here again we see the need for the reconciliation of moral thinking and prudent thinking, and so we are back to healing this split in rational thinking by means of the Ideas of the Highest Good and God. This is the original logic in the CPrR. And surely this is why Kant suggests to Spinoza that he should just assume the existence of God and thereby to ease his striving to be a good and upright man.