1. The ultimate material cause of the universe is some sort of elementary particles. These particles themselves, as far as we know right now, have no substructure, thus are not composed of other particles, and so are simple.
As a result, the term “simplicity” has a very clear unambiguous meaning. It’s a property of an electron. When we ascribe simplicity to God, we speak neither equivocally nor univocally (since divine simplicity need not be exactly like an electron’s), but analogically.
2. Next, I have explained how the efficient cause of X — that which makes X work and explains how it works — is the system of which X is a material cause. I even suggested an argument for the existence of God from this, which I now withdraw.
However, we can at least see that the working of no system within the universe can be fully understood without considering the universe as a whole. And just as parts of the universe are law-bound, so the universe as a whole is not and is efficiently free.
This is because there is no law that the universe as a whole must be this as opposed to that.
Complete freedom then is an easily tractable and meaningful notion. When we say that God is free, we again make an analogy to the freedom of the universe.
3. Further, by studying our own human nature and via introspection, we understand that a human being is a unity. The complexity of neither the body nor the soul destroys this unity. A healthy human being is sublimely one or one person.
There is nothing mysterious about oneness: we humans embody it sufficiently well to grasp the point. When we argue that God is one, we speak analogically from the unity of a man. The analogy is now weaker, since the divine unity is so comprehensive.
4. In regard to the formal cause, human beings make all sorts of art. Some of this art is beautiful or let us say good. But how much greater is the maker than the thing made! The goodness of the art is a pale reminder of the goodness of the artist.
It is then entirely meaningful to speak of the goodness of God whose art is the created universe, though now our analogy is strained almost to the breaking point, because the divine goodness is unique and causes “good things” via “self-diffusion” of itself. Hence no one is good but God alone, yet for all that we are still able to apprehend and judge God’s formal cause.