 This demand for the unconditioned, according to Kant, links up with a demand for some ultimately necessary being. Reason, that is, ceaselessly demands the ground of all the contingent beings in existence, and will not rest until it settles on the absolutely necessary being which grounds them. The idea of the ens realissimum plays a singular role in satisfying this desire of reason, for of all concepts, it is that “which best squares with the concept of an unconditionally necessary being” (A586/B614). In fact, according to Kant rational theology is based on the coincidence of the rational demands for a supremely real being and for a being with absolutely necessary existence. If the movement to the idea of God, as the unconditioned ground, is inevitable, it is nevertheless as troublesome as the other rational ideas: