I got caught a few days ago in a paradox which arose from a combination of philosophical statements I am used to making. I argued that the definition of an abstract object was of a thing which exists or subsists, but which has no causal relations (they are causally effete). A friend argued that if the Platonic form ‘Justice’ exists then clearly it ’causes’ some act to be ‘Just’ – I responded that at most this could be an example of a formal cause or something like that, but that abstract objects don’t have any efficient causal relations or capacities. Just then, I was reminded that I also typically say that God is concrete rather than abstract, because God is not causally effete. However, on the doctrine of divine simplicity enunciated by the Roman Catholic Church, God has no accident-essence distinction, and has no causal relations (since causal relations inhere their relata individually). So, God has no causal relations to the world. Yet, I said that the definition of an abstract object was of a thing which does not and cannot have causal relations. According to this strict construal, God is not concrete but abstract.
However, God is clearly not causally effete, so perhaps it would have been better for me to say that the definition of an abstract object is something which is (efficiently) causally effete. Alternatively we could just say that God is neither abstract nor concrete, but then we would have to say that these two concepts are not disjunctively exhaustive. That sounds problematic because they sound as though they are just opposites: a concrete object is one which cannot in principle have causal relations (of the efficient variety), and an abstract object is one which can in principle have causal relations (of the efficient variety). So, let’s stick to saying that God is not causally effete, and therefore that God is concrete, even though God is an A-typical case of concretism.