Inside and outside

Thomistic simplicity, as I understand it, isn't a single claim but a set of claims. It includes the claim that God's attributes are mutually identical. 

We might begin by asking what it means for something to be a composite object. What makes it composite? What are parts? 

Suppose we begin with this example. Take a block of cheese. It has an inside and outside. Cut it in half. The halves have an inside and outside. Cut the halves in half. The quarters have an inside and outside. Up to a point, the process is repeatable, although cheese isn't indefinitely divisible. There's no subatomic cheese! To be cheese, it must exist at a certain scale and complexity. There are no quarks or atoms made of cheese. 

The point, though, is that we can think of a composite object as an object with an inside and outside. Objects with surface boundaries. These can be taken apart. And the parts have surface boundaries. So the process of disassembling a composite object into its components is a progressive miniaturization, where the inside/outside relation continues at ever lower scales of magnitude. Where does it end–or does it? In physics, the Plank length is the lowest bound, although that's an artificial stipulation. 

That raises the question of whether every object, however small, has an inside. That's a philosophically and scientifically important, interesting, and difficult question. However, I don't have to answer that question since I'm merely using this illustration as an opening gambit. 

I began with an example of a physical object or solid object. But proponents of Thomistic simplicity subscribe to classical theism. In classical theism, God is akin to an abstract object. Timeless and spaceless or illocal. 

Suppose that God's attributes are distinct. Not mutually identical. Does that make God a composite being? Are attributes parts? 

It doesn't make much sense to say God has an inside and outside. It doesn't make much sense to say the divine attributes, even if distinct, have an inside and outside. So they can't be parts in that sense. So in what respect is an object a composite object if it lacks an inside and outside? In what respect can parts be parts if they lack an inside and outside?

If we view God as a discarnate mind, then you might say minds are insides without outsides. It's all on the inside (so to speak). Minds are essentially internal or interior. Self-referential. They have no surface boundaries. That's not what individuates and differentiates one mind from another. 

Admittedly, I'm using a spatial metaphor. If we drop the metaphor, then the inside/outside relation is literally inapplicable to minds. 

Likewise, if God is a discarnate mind, then divine attributes are mental properties. But even if distinct, mental attributes aren't parts of a composite entity. Mental properties have no inside and outside. 

This is also germane to the Trinity. In the case of concrete individuals or particulars, one individual is external to another individual. So the inside/outside relation reasserts itself in that context. 

But the Father isn't literally external to the Son and Spirit. In fact, there's a sense in which (albeit figurative or analogical) each member of the Trinity is "inside" the other two persons, and vice versa.