What is the ultimate explanation of the universe? Is there something beyond the universe that accounts for its existence, or does the universe contain no explanation for its being, and simply is? For a metaphysical naturalist, who believes that the universe is a closed system—that is, there is nothing that transcends the natural world that could be labeled supernatural—the former is rejected and the latter accepted. There really is no other option for the naturalist, if he wants to remain faithful to naturalism. If the universe is all there is and nothing outside the universe can explain its existence, then it must simply be viewed as the ultimate brute fact. That is to say, the universe just exists, with no rhyme, reason, or explanation.
Yet, I maintain that this position can be demonstrated to be untenable. One way (there are others) to demonstrate this is by examining the nature of the universe itself. You see, if we can show that the universe is contingent, then, by the definition of contingent, we will have shown that the universe requires something outside itself to explain its existence. But, how can we go about demonstrating that the universe is contingent? Well, how about we begin by defining our terms.
There are many different definitions of a contingent being: (1) that which could possibly have not existed, (2) that which could cease to exist, or (3) a being whose essence (what it is) is distinct from its existence (that it is). It seems that we could utilize any of these definitions, though (1) would seem harder to predicate of the universe. Moreover, (2) seems easy to predicate of the universe, yet it seems difficult to infer from this definition that the universe therefore requires an explanation for its existence from something outside of itself. Hence, I feel it easier to pursue our inquiry with the utilization of (3).
So, something is contingent if what it is is distinct from the fact that it is. Take, as an illustration, a basic chair. The essence of the chair is that it provides a seat (among other things). The existence of the chair is the fact that it has being—that is, that it actually exists. The fact that the chair’s essence is not identical to its existence demonstrates that the chair is contingent. Why, you might ask? Well, because if it is not the essence of a chair to exist—which it certainly is not since my concept of a chair shares the same essence, yet does not exist—then the explanation for its existence must lie outside the chair. That is to say, we cannot examine the nature of the chair and deduce the reason for its existence; we must look elsewhere. Hence, the chair is contingent.
Now, let us turn our attention back to the universe. Everything inside the universe is, just like the chair, contingent. There is no existent thing in the universe whose essence is identical to its existence. But, if the universe is simply the totality of all these contingent things (e.g. galaxies, planets, rocks, humans, stars etc.) then how can the universe fail to be contingent itself? Now it is at this point that one is charged with the fallacy composition—that is, fallaciously reasoning from the part to the whole of a thing. If every brick in a wall weighs one pound, it doesn’t logically follow that the wall itself weighs one pound. Similarly, just because every thing in the universe is contingent, this doesn’t entail that the universe as a whole is contingent. However, this is simply a misunderstanding. Not every inference from a part to a whole is fallacious. For instance, if every city in a country lacks electricity, then the country as a whole also lacks electricity. Similarly, a compiled group of things whose essences are distinct from their existence does not seem to rid the group itself of this distinction. The group as a whole still has an essence—namely, being that very collection of things—which is not identical to its existence—that it does in fact exist. And therefore, the universe, which contains all contingent things, would have to be contingent.
Now, if the universe is contingent, then there must be an explanation for why the universe exists, since the explanation is not to be found in the essence of the universe itself. Stated thus, we see that the universe cannot, contrary to the naturalist, just be. Rather, there must be an explanation for the existence of the universe, and it must come from outside the universe. The universe then is not a brute fact—if there is any such thing—rather, it is something that exists, not out of its own necessity, but out of the necessity of another.