It seems inevitable in the course of analytic treatments of philosophy of religion that we must endure talk of “possible worlds.” The deployment of “possible worlds” strike me as problematic for a number of reasons. It tends to conflate metaphysical and logical possibility, it attempts to solve real world questions with the fancies of the imagination, it often assumes that the actual is grounded in the possible (and vice versa) and it grants far too much weight to the powers of abstraction in penetrating the nature of the world.

I couldn’t entirely fend off these misgivings as I read through Dale Tuggy’s continuing arguments in his ongoing debate with William Vallicella. This particular debate, however, can be resolved on simpler grounds. The central question concerned God’s metaphysical simplicity seems to be easily resolved given what Tuggy has already ceded. As soon as Tuggy admitted a real distinction between essence and existence, Tuggy has placed himself on the ineluctable logical sequence towards God’s simplicity and necessity.

Accidentality and Priority of Being

God’s simplicity can inferred from the facts that existence is accidental to and prior to the essences of composite things. To say that existence is accidental is simply to say that it is not the nature of a thing. Knowing what giraffes is doesn’t tell you anything about whether any particular giraffe actually exists, because existence is not the nature of the giraffe. One must ascertain the existence of giraffes by seeking them out, or by depending on the reports of others who have sought them out.

The intrinsic difference between essence and existence is usually the most difficult point to establish on the way toward demonstrating God’s simplicity and necessity–debates on the subject have raged since the 13th century–but Tuggy has already granted the point. Being is an accident for things in the sense that it is extrinsic to their natures.

Being’s priority means that being is not only different from a thing’s essence, but it ontologically prior to that essence, rather than subsequent to the essence in the way of other accidents. The existence of a thing is not something subsequent to the thing’s nature as (to use a traditional example) risibility follows from human nature. Neither is it subsequent in the sense that it modifies the thing as other accidents do. For a thing must first exist to have a nature or possess accidents. Existence is, then, prior to the entire essential order, which includes not only the nature of a thing, but its properties and its qualitative and quantitative accidents.

The priority of existence over essence (again, in the sense of the entire essential order) cannot be escaped by making existence merely part of a nature. If existence was part of a thing’s nature, the other parts would not be. Existence pervades the entirety of the thing, for whatever quality of the thing one places outside the thing’s existence, does not exist.

Therefore, composite things cannot account for their existence. They always come to be from causes that precede them. They cannot be responsible for their existence, because in order to cause themselves to be, they must first exist. (Of course, “first’ is in the sense of causal priority, not necessarily temporal priority). Things that aren’t simple exist contingently.

The Necessity of an Uncomposed Being

If existence is prior to essence in composite things, then there must be a being whose existence and essence are identical. No finite series of composite things could account for the existence of any member of the set of composite things any more than a single composite thing could. Nor could an infinite series of composite things explain the existence of any composite thing, because the power of each to act as an efficient cause depends on there being a being whose existence is not contingent. As Barry Miller has pointed out, the logical form of such a series is A if (B if [C if {D if |…|}]). (For a more detailed explanation, see here.)

If God is the cause of the existence of everything else, then God’s existence cannot be distinct from his essence. Otherwise God is in the same position as every other composite being. If God were composite, then he could not account for his existence, since it is causally prior to him. Another way of saying this is that while being is an accident in composite things, in God, being is a nature.

These, anyway, are the contours of the traditional argument for God’s simplicity, arising mostly from Aquinas De Ente. God’s nature is to be, or to put it another way, God’s essence and his existence are not really distinct. This does not mean that we grasp God’s essence, and, in fact, we do not. For us, God’s essence and existence most often remain conceptually distinct, and we can only get at what God is through analogy, metaphor, meditative prayer, and worship. But these are not required to grasp the argument for God’s simplicity.