These bear upon the reconciliation of grace with free will. The chief theological systems involved are: Augustinianism, Thomism, Molinism, Congruism, and Syncretism. Augustinianism and Thomism hold that grace derives its efficacy from its own intrinsic nature (ab intrinseco), the former ascribing it to a moral and the latter to a physical influence of grace upon the free will. Molinism and Congruism teach that grace is efficacious extrinsically (ab extrinseco), deriving its efficacy from the free will prepared and assisted by grace. Congruism, however, explicitly postulates that the grace be congruous (congrua), that is, adapted to the nature and circumstances of the recipient. For the infallibility of the connection of grace with the consent of the free will, both fall back upon God's foreknowledge through the scientia media. Syncretism defends the intrinsic efficacy of grace for difficult actions, and extrinsic for such as are less difficult.