Aquinas’s Epic Fail
Thomas Aquinas, the 13th-century Dominican theologian, wrote a book we call The Five Ways. It is supposed to be a kind of manual for missionaries. It gives five proofs of the existence of God, each of which Aquinas thinks will convince non-believers to accept the Catholic “omni-God” (the monotheistic god who is all-powerful, all-knowing, all-good, and so on: “omni” is Latin for “all”).
The whole thing is a stunning failure. Each of the Five “Ways” is really the same argument. The argument is Aristotle's (not Aquinas’s), tarted up in Christian clothes. None of the versions succeed in proving their conclusions. And then Aquinas makes it worse by tacking on to each of them the non sequitur that whatever conclusion we get from each argument, “this everyone knows to be God.” Still worse, there’s a further hidden assumption in this formula, since Aquinas really means, “And this everyone knows to be the Christian version of an omni-God.” In short, none of the five arguments prove what Aquinas claims he has proved. Fail.
Aquinas is a great source for teaching argument (how to analyze an argument, how to arrange an argument in premise-conclusion structure, how to find and critique assumptions, and what not to do yourself when you are trying to construct an argument). But as attempts to prove something about the supernatural, the Five Ways just don’t work. Aquinas is also important to teach because arguments like the ones he gives have been influential in Western culture, especially in philosophy and theology. But we don’t teach these arguments because they are correct. They just aren’t. In a sense, The Five Ways is an example of how not to do philosophy—or at least, it is an example of a style of philosophy that has been superseded now that we have a lot more science and a lot better empirical philosophy. Given this, it is strange to see these arguments so often re-tread in contemporary popular apologetics. (“Religious apologetics” is the name of the branch of philosophical theology that aims to give arguments to prove the existence of God through reason. The Latin root apologia means “a reasoned defense” so apologetics attempts to defend religious belief through reason.)
Here are Aquinas’s Five Ways. (Other commentators give them slightly different names.)
1) The Argument from Motion
2) The Argument from Efficient Causation
3) The Argument from Contingency
4) The Argument from Gradation
5) The Teleological Argument
Arguments 1 and 2 are essentially the same argument about causes; and likewise, arguments 3, 4 and 5 are very similar to each other. In fact, all five arguments have a family resemblance since they depend on similar assumptions and argumentative moves, including the Principle of Sufficient Reason, disallowing infinite regress, and invoking a chain of causes. Essentially, they are all just variations on the Cosmological Argument that comes from Aristotle.
In each case there is a sub-conclusion of the specific argument:
1) There exists an Unmoved Mover
2) There exists a First Cause
3) There exists a Necessary Being
4) There exists a being with Absolute Perfection
5) There exists an ultimate Reason for the existence of the universe
Before we get to the criticisms of the Five Ways, it might be useful to show one of them in detail. Let’s examine (2) the argument to the existence of a First Cause. If you look in other commentaries, you might find a slightly different reconstruction, but I think this one is fair to the original and clear for non-experts.
There is a current “state of affairs” in the cosmos, the way things are now.
<Principle of Sufficient Reason>: Nothing comes from nothing.
<From 1 and 2> Therefore, the current state of affairs had a cause.
<Corollary of 3> It seems reasonable that the current state of affairs was caused by the prior state.
Then, for any state of the universe, n, the cause of n is the prior state, n-1.
This leads us to conclude that there exists a chain of causes going backwards from the present state to earlier and earlier states.
<Aristotle’s Principle>: There can be no infinite regress.
<From 6 and 7> Therefore, the chain of causes does not extend to infinity.
<Corollary of 8> There must exist a First Cause, that is, a cause that led to the rest of the universe but which itself is uncaused.
<Anselm’s tag> This, everyone understands to be (the omni-)God.
By 9 and 10: Therefore, the omni-God exists.
In this reconstruction, I have isolated step 10 as its own move in the argument. Aquinas tacks on the same additional overarching conclusion to each of his five arguments, “And this, everyone understands to be God.”
This additional conclusion is huge leap in each case. We need to be talked into the idea that the thing that moves other things without itself being in motion is the Christian omni-God. Aquinas doesn’t even try to prove the connection. The same goes for the other four arguments: There is no good reason to suppose that the First Cause of the universe is the Christian omni-God as opposed to any other religion’s creative god, or even a deist “divine power” that is entirely unlike the Christian God. There is no particular reason to think that a being who exists necessarily, or one that is perfect goodness, etc., is identical with the God of the Old or New Testament. So, in this respect, any other criticisms aside, the Five Ways do not prove their conclusions; they don’t even come close. It is possible that the conclusions of each of the Five Ways could prove the existence of five different beings. There is no good reason (from these arguments themselves) to assume that their conclusions are all referring to the same entity. And there’s no reason at all to think that those conclusions are referring to the Christian God.
But the conclusions of each of the Five Ways are themselves individually problematic, anyway. The arguments to support them make metaphysical assumptions which have become commonplace now and so some people believe them to be true (or even obviously true). But in fact, those assumptions are arbitrary and as a result the arguments do not prove anything.
Take the Principle of Sufficient Reason (PSR), which plays a key role in each of the Five Ways. The PSR asserts that there is a cause of everything that comes about, and that the cause must contain enough (“be sufficient”) to bring about the event or thing. Cosmological Arguments use the PSR to reason backwards along the chain of causation: If this thing now exists, it had a cause before it, and that had a cause, and that had a cause, and so on.
Now, it is true that we usually think that in ordinary experience, everything that happens has a set of antecedents that bring the thing about. In our experience, or so we think, everything that happens, has a cause of it happening. I’m not convinced that we really do know that every effect has a cause, or that each cause is sufficient to bring about its effect, however. That is in part because “contains enough” seems to me to be ill-defined. In part we lack this knowledge in many cases because we usually are not paying attention to those things that could be the causes of some future effect (since we don’t know they are relevant until they contribute to the cause of something we do later pay attention to). There are lots of things in our experience that we cannot explain, too, which is precisely to say that we do not know what their causes were.
David Hume argues convincingly that PSR is not a logical truth and that it is not an empirical generalization gathered from experience. Rather, he says, it is effectively a pre-condition of how humans think—something that is typically effective for the kinds of reasoning we do in ordinary life, but which is not guaranteed to be true in all cases or even to apply to cases of kinds we have never experienced (like the case of the origin of a universe).
Besides all of which, our ordinary experience is not very extensive, and we are often wrong in our causal reasoning (this was especially true before the rise of science). Most importantly, we have no experience at all of the kinds of things that might have happened in the first moments of creation. Maybe “ultimate coming into existence” has a cause—but maybe it doesn’t? How could we know? This is not to deny that there is a cause of existence, but to point out that the Principle of Sufficient Reason assumes that there must be one, ruling out by fiat the possibility that the first event was uncaused.
The Principle of Sufficient Reason also runs into problems when it is combined with other assumptions in these arguments, particularly the assumption that there cannot be an infinite chain of causes. This idea, too, goes back to Aristotle, who asserts it as a personal aesthetic preference. He just doesn’t like infinite chains of causes. An explanation that relies on an infinite chain of causes, going back and back without stopping, Aristotle calls an infinite regress. An explanation that involves an infinite regress never “reaches bottom” and so doesn’t explain what it is trying to explain, and Aristotle doesn’t like that. But nothing besides this preference rules them out. It is perfectly possible that there could be no beginning of the universe, and hence no first mover; it is possible that the universe caused itself and didn’t require a first cause that is itself uncaused; it is possible that there is no perfect being; and so on. The assumption “no infinite regress” makes it so that each of the Five Ways must conclude with a first or best of whatever kind of thing that Way is considering. Without that assumption, which is never given a justification in Anselm, the argument simply does not prove its conclusion. To put the point another way, if we throw out the unjustified assumption that infinite regresses are impossible (as opposed to explanatorily incomplete, or pragmatically useless, or aesthetically undesirable), it could be that the universe has no first cause because it has always existed, eternally, in some form (perhaps an infinite series of Big Bangs and Big Crunches, or something else we have not imagined).
You can also see a problem with each of the Five Ways if you consider this: The PSR says everything has a cause. The “no infinite regress” principle says something does not have a cause. In other words, these two assumptions, besides being unjustified, contradict each other. Logicians say “anything follows from a contradiction” but they mean “follows” only in the sense of it not being possible for the conclusion to be false when the premises are all true. Such arguments are valid on a technicality. When the premises are contradictory, they cannot all be true, and so the conclusion from an argument containing a contradiction is never proven true (that is, such arguments cannot be sound).
Aquinas’s Five Ways do not just fail, they fail epically.
