The Moral Argument
Kant is the first major philosopher offer a “moral” argument for the existence of God. While he believed that extant, traditional proofs were all defective, Kant held that the existence of God was nevertheless a rational belief, indeed more rational than agnosticism or atheism. God; personal freewill and the immortality of the soul were indeed matters of faith and not ordinary speculative reason. Nevertheless this was a rational faith. (Remember he is an Enlightenment kind of guy.)
It may be helpful to review what he believed that speculative reason must be limited to the phenomenal realm of sensation. See notes on Kant’s epistemology.
From an analysis of the necessary presumption of Practical reason however. We are morally/ rationally completed to believe in freewill, the immortal soul and God. The way these arguments are supposed to work is Kant demonstrates that moral experience is absurd unless one presumes certain things about reality. Since it is always irrational to embrace an absurdity, we are thereby completed to embraces the alternative, that is, to accept the presumption (despite not having speculative evidence for it).
Remember for Kant, “ought implies can.” But this we mean that if the sentence “He ought to tell the truth.” is true, then the sentence “He can tell the truth.” is also true. And if the sentence “He can tell the truth.” is false, then the sentence “He ought to tell the truth.” is also false. This is simply the logical relation of implication. But Kant would claim, I am can be (morally) certain that the sentence “He ought to tell the truth.” is true. Therefore I can be equally (morally) certain that the sentence “He can tell the truth.” is also true. This is, roughly, Kant’s argument for freewill as a necessary postulate of moral experience.
Similarly Kant reasoned that the Moral Law commands us to seek our own moral perfection. (It is not enough to be a little bit moral; we ought to be morally perfect.) Further, people ought to be happy proportional to their moral worth. (This was his criticism of Utilitarianism.) But Kant was well aware of the fact that "there is not the slightest ground in the moral law for a necessary connexion between morality and proportionate happiness in a being that belongs to the world as a part of it." (KP 124) The only postulate, therefore, that will make sense of man's moral experience is "the existence of a cause of all nature, distinct from nature itself," i.e., a God who will properly reward moral endeavor in another world. In a godless universe morality is an absurd demand.
This is not merely "wishful thinking" but has the force of a moral imperative, a moral imperative which would be absurd unless moral agents were capable of moral actions (i.e. free will) and infinite perfection (i.e. immortality) and there were a arbiter of justice (i.e. God) who would make happiness proportional to moral worth (something like heaven) in the end (i.e. immorality).
Kant thought the moral law could be established by reason (that is the right thing to do is the right thing to do irrespective of God), God was necessitated by our moral conviction that virtue ought to be rewarded. A fair amount turn on the phenomenology of moral experience here. It is the felt certainty. We must begin with the experience and seek its rational ground. As we shall see with Fries and later with Otto, the suggestion that moral and aesthetic experience gesture at the transcendent was an attractive positions for post-Kantian philosophers.
More recently, an somewhat different from a moral argument for the existence of God has be formulated. Here is a version Hastings Rashdall’s (1858-1924), which claims our commitment to an objective moral law requires a commitment to a perfect moral mind… and that all men call God. J
· An absolutely perfect moral ideal exists (at least psychologically in our minds).
· An absolutely perfect moral law can exist only if there is an absolutely perfect moral Mind:
o (a) Ideas can exist only if there are minds (thoughts depend on thinkers).
o (b) And absolute ideas depend on an absolute Mind (not on individual [finite] minds like ours).
· Hence, it is rationally necessary to postulate an absolute Mind as the basis for the absolutely perfect moral idea.
In support of the objectivity of the absolute moral idea Rashdall offers this reasoning:
· Morality is generally understood as objectively binding.
· Mature minds understand morality as being objectively binding (i.e., binding on all, not just some).
· Moral objectivity is a rationally necessary postulate (because something cannot be judged as better or worse unless there is an objective standard of comparison).
· Objective moral ideals are practically necessary to postulate.
As Hastings Rashdall put it
But to the man who regards all spiritual life as a mere inexplicable incident in the career of a world which is essentially material (were it not for the human and animal minds which it is known to have produced) and as a whole essentially purposeless, there is no conclusive reason why all moral conception of “value,” the very notion that one thing is intrinsically better another, the conviction that there is something which a man ought in do—may not be merely some strange illusion due to the unaccountable freaks of a mindless process or to the exigencies of natural selection. It cannot be said that a man who allowed such doubts to shake or modify his allegiance to the dictates of Morality, where they do not happen to coincide with his actual desires or inclinations, would be doing anything essentially unreasonable. Reasonable conduct would for him mean merely “conduct conformable to his own private reason”: intrinsically or absolutely reasonable or unreasonable conduct could not exist in a world which was not itself the product of Reason or governed by its dictates.
 Hastings Rashdall, The Theory of Good and Evil: A Treatise on Moral Philosophy, 2d ed. (New York: Kraus Reprint, 1971), 2: 211-13.