The doctrine that God is absolutely simple derives from the metaphysical considerations that God is a being whose existence is self-explanatory, absolutely perfect, and pure actuality. Prior to Thomas, the doctrine has its most influential formulations in Augustine and Anselm.[1] According to Thomas, God is his essence and his essence is to exist.[2] If the existence of a thing differs from its essence, this existence must be caused either by some exterior agent or by its essential properties.[3] The latter seems to be impossible for nothing, if caused to exist, can be the sufficient and efficient cause of its own existence. Nothing can be self-caused and thus the latter option is insufficient. Therefore, if existence differs from essence then another being must cause existence. This option is also an insufficient explanation for God’s essence and existence because another being cannot cause God because he is the first efficient cause—the uncaused cause.
There are three important claims Thomas commits to concerning the doctrine of divine simplicity.[4]
(1) It is impossible that God have any spatial or temporal parts that could be distinguished from one another as here rather than there or as now rather than then, and so God cannot be a physical entity.
(2) It is impossible that God have any accidental properties.
(3) All of God’s intrinsic properties must be essential to him, it must be acknowledged that whatever can be intrinsically attributed to God must in reality just be the unity that is his essence.
The first claim, (1), removes God from having any spacetime properties.[5] God is completely timeless logically prior and posterior to the moment of creation. From this timelessness it follows that God is absolutely immutable and eternal, which are all entailed from simplicity.[6] The immutability that Thomas is advocating functions with respect to God’s intrinsic esse. If God were to be able to change intrinsically that would suggest that God’s goodness and omnipotence could change.[7] An extrinsic change may certainly be compatible with Thomas’ notion of immutability. If God were to apply salvation to agent X then God has undergone an extrinsic change in the sense that agent X was once an enemy of God prior to salvation whereas post-salvation agent X is now a friend of God. This is a relational change that has no effect on the intrinsic esse of God. Thomas would argue that all creatures are really sustained,[8] known, and loved by God, but God would be the same whether creatures existed or not. However, it is difficult to reconcile God’s genuine relationship with contingent beings if this modal distinction is permitted. If it is the case that no modal distinction is possible and that modal collapse is a byproduct of simplicity then God really does stand in genuine relations to created beings and creation since it is not the case that what exists could not have not existed.[9] Thus, God does not really undergo an extrinsic change in creating the world. He just exists; creation and creatures come into existence with a real relation to God by being caused by God.[10] This simply makes extrinsic change superfluous to God.
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