Immanuel Kant is a rationalist, and, as such, he places supreme importance on reason. However, his application of reason to issues of faith and the divine unfolds in interesting ways, given that it is a tendency of the rationalists to collapse into dogmatic reasoning. Indeed, as is well-documented, Kant, as an Enlightenment-era thinker is specifically opposed to rationalist dogmatism (and metaphysics before him), and so in his critical thought he avoids simply positing the existence of God dogmatically or axiomatically. This is in contrast to his early, pre-critical attempt to argue for the existence of God by way of rational reflection.
So what is his contribution to the God question, then, exactly? To start, he rejects arguments such as the ontological argument; then, much of his critique is levelled at religious practice in its formalized, ritual sense and all the attendant pomp and circumstance that actually (in his view) distorts any possible communion with a potential God. The ontological argument does, of course, veer in the direction of claims on an ens realissimum (as an anthropomorphized thing-in-itself).
However, faith has a pragmatic character in Kant’s thought, where, despite the problems associated with knowledge of the existence of God, the activity of faith is indexed to moral law. This is the case regardless of the real existence or non-existence of God. Indeed, the objective nature of the good in Kant (as categorical imperative) bears analogues with the notion of a mind-independent God-like entity (as deified thing-in-itself). In addition, he also articulates a ‘highest good’ that has ideal and absolute properties, again testifying to its objectivity and, subsequently, its God-like character. It should also be noted that this God qua moral ends has a teleological character.
The second question is on Kant and a belief in the existence or non-existence of God, where this can also be approached from the perspective of the thing-in-itself and the distinction between the noumenon and the phenomenon. Firstly, making a claim on either belief or non-belief is problematic. For, claiming that God does not does not exist confers upon Him negative qualities, as indeed does belief as a conferring of positive qualities on God—unless, of course, God (and any attendant question of belief) bears a noumenal quality. However, the preference of a belief in God is indexed to the design-orientated nature of Kant’s entelechy, for, where rationality is indicative of the triumph of reason and where the moral disposition is objective and innate, so the analogue of this disposition must allow for God-like attributes.
Of course, the early pre-critical Kant should also be mentioned, for it would be a problem to simply assume that his critical philosophy bears more weight. A key text of the pre-critical period is The One Possible Basis for a Demonstration of the Existence of God, where he argues that any attempt to rationally conceptualize God is actually self-defeating in its subjecting an extra-conditional God to conditions. Thus, the careful rationalist should delimit his enquiry to the realms of conditions, understanding that any attempt to transgress this boundary immediately results in the self-destruction of reason. This is certainly indicative of a somewhat ungainly precursor to his critical position on the advancement in the direction of the thing-in-itself. So, the rationalist stands back from any such movement, rejecting the ontological argument (where he thinks that existence is not a predicate), whilst then proceeding to articulate a rationalist conception of God that is grounded in his moral philosophy. This latter conception is then congruent with the mature metaphysics that he espouses, in his attempted emancipation of the discipline and its philosophical apostles from its ‘self-incurred tutelage’.