God may fall out as an argued necessity in some cultural constructs; Kant pointed-out that this is what human reason concludes when beginning with the applicable starting axioms of such systems. According to Kant, God in the end is 'the representation of our own capacity to give ourselves the moral law through reason'. Just as an intellective process (with initial biases) may output that it is a necessity to reject something like solipsism, one of them may similarly output that God is unavoidable. People who are transcendental realists (who metaphysically reify the space of experience or the external, phenomenal world of extrospection) then unsurprisingly also depict God as a visual-conforming creature, usually with anthropic characteristics.
Paul Guyer -- "In the latest stages of this work ... Kant returned to the broadest themes of his philosophy, and tried to develop a final statement of transcendental idealism. Here he argued that 'The highest standpoint of transcendental philosophy is that which unites God and the world synthetically, under one principle' - where that principle is nothing other than human autonomy itself. God and the world are 'not substances outside my thought, but rather the thought through which we ourselves make these objects'. The world is our experience organized by categories and laws of our own making, and God is the representation of our own capacity to give ourselves the moral law through reason. The moral law 'emerges from freedom...which the subject prescribes to himself, and yet as if another and higher person had made it a rule for him. The subject feels himself necessitated through his own reason...'. This is a fitting conclusion to Kant's philosophy of autonomy."
While a noumenal circumstance (where items like God, freedom, immortality might be available] was declared unknowable in the context of Kant's theoretical / speculative philosophy, in practical philosophy it is possible to project argued necessities upon it, because therein there is no pretense of providing positive evidence or confirmation.
Kant -- "But as will be shown, reason has, in respect of its practical employment, the right to postulate what in the field of mere speculation it can have no kind of right to assume without sufficient proof. For while all such assumptions do violence to [the principle of] completeness of speculation, that is a principle with which the practical interest is not at all concerned. In the practical sphere reason has rights of possession, of which it does not require to offer proof, and of which, in fact, it could not supply proof. The burden of proof accordingly rests upon the opponent. But since the latter knows just as little of the object under question, in trying to prove its non-existence, as does the former in maintaining its reality, it is evident that the former, who is asserting something as a practically necessary supposition, is at an advantage. For he is at liberty to employ, as it were in self-defence, on behalf of his own good cause, the very same weapons that his opponent employs against that cause, that is, hypotheses. These are not intended to strengthen the proof of his position, but only to show that the opposing party has much too little understanding of the matter in dispute to allow of his flattering himself that he has the advantage in respect of speculative insight. Hypotheses are therefore, in the domain of pure reason, permissible only as weapons of war, and only for the purpose of defending a right, not in order to establish it. But the opposing party we must always look for in ourselves. For speculative reason in its transcendental employment is in itself dialectical; the objections which we have to fear lie in ourselves. We must seek them out, just as we would do in the case of claims that, while old, have never become superannuated, in order that by annulling them we may establish a permanent peace."
Kant -- ". . . But when all progress in the field of the supersensible has thus been denied to speculative reason, it is still open to us to enquire whether, in the practical knowledge of reason, data may not be found sufficient to determine reason's transcendent concept of the unconditioned, and so to enable us, in accordance with the wish of metaphysics, and by means of knowledge that is possible a priori, though only from a practical point of view, to pass beyond the limits of all possible experience. Speculative reason has thus at least made room for such an extension; and if it must at the same time leave it empty, yet none the less we are at liberty, indeed we are summoned, to take occupation of it, if we can, by practical data of reason. This attempt to alter the procedure which has hitherto prevailed in metaphysics, by completely revolutionising it in accordance with the example set by the geometers and physicists, forms indeed the main purpose of this critique of pure speculative reason. It is a treatise on the method, not a system of the science itself. But at the same time it marks out the whole plan of the science, both as regards its limits and as regards its entire internal structure."
Otto F. Kraushaar -- "Kant ... shows ... the forms of sensibility and understanding cannot be employed beyond experience in order to define the nature of such metaphysical entities as God, the immortal soul, and the World conceived as a totality. If the forms are valid in experience only because they are necessary conditions of experience, there is no way of judging their applicability to objects transcending experience. Thus Kant is driven to the denial of the possibility of a science of metaphysics. But though judgments of metaphysics are indemonstrable, they are not wholly useless. The 'Ideas of Pure Reason' have a 'regulative use', in that they point to general objects which they cannot, however, constitute. Theoretical knowledge is limited to the realm of experience; and within this realm we cannot know 'things-in-themselves', but only the way in which things appear under a priori forms of reason; we know things, in other words, as 'phenomena.'
"But reason is not limited to its theoretical use. Besides objects of cognition and thought, there are also those of will and feeling. Kant's 'practical philosophy', the real foundation of his system of transcendental idealism, centers in a striking doctrine of freedom. Even in its theoretical use reason is a law-giver to Nature, in that the data of sense must conform to the forms of the sensibility and understanding if Nature is to be known at all. But in moral experience, as Kant shows in the Critique of Practical Reason (1788), the will of a rational being is directly autonomous -- a law unto itself. ... As phenomenal beings we are subject to the laws of nature and reason, but as pure rational wills we move in the free, noumenal or intelligible realm, bound only by the self-imposed rational law 'to treat humanity in every case as an end, never as a means only.'"
