Divine simplicity

The doctrine has roots in Platonic philosophy and was systematized in Christian theology by Augustine and, most fully, by Thomas Aquinas in the Summa Theologiae. For Aquinas, God's simplicity was not one attribute among many; it was the ground of all the others. Because God has no parts, God cannot be composed of substance and accidents, of form and matter, of essence and existence, or of one attribute and another. What we call God's wisdom, God's goodness, and God's power are not three distinct things; they are one and the same reality, which we describe under different aspects because our finite minds cannot grasp the undifferentiated whole at once.

The motivation for the doctrine is partly scriptural (God is one) but mostly philosophical. If God had parts, those parts would be more fundamental than God himself, and God would depend on them for his existence — which is incompatible with aseity. If God's existence were distinct from his essence, then God's existence would have to be caused by something else, which is incompatible with God being the uncaused first cause. Simplicity is the position that preserves all of these classical divine attributes simultaneously.

The doctrine has always been philosophically difficult and is one of the main reasons contemporary philosophers sometimes reject classical theism. If God's wisdom is identical to God's power, and both are identical to God himself, then everything we want to say about God collapses into a single undifferentiated claim. The contemporary philosopher Alvin Plantinga called divine simplicity "a dark saying" and argued that it renders God into something more like a property than a person, which seems incompatible with the God of ordinary religious practice.

Thomists and their successors defend the doctrine by distinguishing the way we think about God (conceptually, with multiple attributes) from the way God actually is (simply). But this defense often ends up conceding that we cannot actually understand what divine simplicity means from the inside; we can only describe it apophatically, saying what it is not.

For a secular reader, divine simplicity is important because it is the specific metaphysical commitment that distinguishes "classical theism" from more anthropomorphic pictures of God. When a theologian says their God is not a "being among beings," the technical move they are making is a simplicity move. It is also a useful reminder that classical theists often agree with atheists that the cartoon anthropomorphic God does not exist — they are defending something much stranger and more metaphysically austere.