Abstract
In his early writings, Kant describes the existence of an individual substance as containing in itself no relation to other substances. So the existence of an individual substance is not bounded with any certain world, and it can possibly belong to another world and be in relation to other substances than in this world, and it is entirely contingent that a substance belongs to this world and is in relation to other substances. And God is the ground for the correlation of the substances belonging to a world, and thus it is a key to the problem of contingency.
But in the critical period Kant constructed an entirely different ontology from that of his early days, and tries to grasp the existence of being in terms of the relation of necessarily synthesized perceptions, given to sensitivity as what are Actual. Thus the concept of the God, as a key to the problem of contingency, finds no room in such an ontology.
But the synthesis of perceptions can never make an absolute Totality, and, compared with the Idea of absolute Totality by reason, every given perception (or the synthesis of them) can be contingent. Such kind of comparison, and the judgment of what is Actual, is the problem of critique (not of the system). Kant devoted his Third Critique to such problem, and there it survives a concept of the God, as a key to the problem of contingency.
