Deconstructing Thomas Aquinas' Five Proofs of a Creator

Aquinas is a figure held up by many Christians as the paragon of sophisticated apologetics. Given that he affirmed as a matter of church doctrine that demons cause bad weather, that may be confusing to many of you. Don't worry, you're not alone.

Remember that a great many Christians today hold up figures like Ken Ham, Ray Comfort and Kent Hovind as unparalleled geniuses. The criteria to be considered an intellectual in Christendom weren't, and still aren't very exacting.

Besides his bold, but wrong proclamations about weather which must've seemed irrefutable to someone with no knowledge of the water cycle, Aquinas' five proofs of a creator were based on various other assumptions that also no longer hold up in light of recent scientific discoveries.

The first proof, for example, assumes that the cause of the universe must be intelligent:

1. Our senses prove that some things are in motion.
2. Things move when potential motion becomes actual motion.
3. Only an actual motion can convert a potential motion into an actual motion.
4. Nothing can be at once in both actuality and potentiality in the same respect (i.e., if both actual and potential, it is actual in one respect and potential in another).
5. Therefore nothing can move itself.
6. Therefore each thing in motion is moved by something else.
7. The sequence of motion cannot extend ad infinitum.
8. Therefore it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God.

The assumption that the prime mover must be an intelligent being (rather than a natural phenomenon) does not follow: every natural object we have discovered the origin of has been proven to form by unintelligent natural processes. There is no good reason why that pattern should not extend back to the big bang.

Aquinas did not know of these processes. He made a very natural (but wrong) inference that only intelligent beings can create apparent design, because all of the designed objects he encountered in his life were products of deliberate human engineering. Many Christians today still make that error in reasoning.

The second proof is a sort of extension of the third. Rather than extrapolating from present day backwards to the first cause, it observes that this causal chain must terminate at some point to avoid infinite regress (as this requires an infinite amount of time, which means it could never arrive at the present day) and further asserts that nothing can cause itself.

1. We perceive a series of efficient causes of things in the world.
2. Nothing exists prior to itself.
3. Therefore nothing [in the world of things we perceive] is the efficient cause of itself.
4. If a previous efficient cause does not exist, neither does the thing that results (the effect).
5. Therefore if the first thing in a series does not exist, nothing in the series exists.
6. If the series of efficient causes extends ad infinitum into the past, for then there would be no things existing now.
7. That is plainly false (i.e., there are things existing now that came about through efficient causes).
8. Therefore efficient causes do not extend ad infinitum into the past.
9. Therefore it is necessary to admit a first efficient cause, to which everyone gives the name of God.

Like a few of the other proofs, this one also asserts that everybody calls whatever the first cause is God. That may have been true in Aquinas' day, but it isn't in the present. Moreover, it is special pleading to say that everything requires a cause except for God.

Certainly some first cause is necessary, but science has already got a good idea of what that probably was, and it doesn't have a curious hatred of homosexuals, of women in positions of authority, or a preference for the scent of burnt animal offerings.

The third proof concerns chains of existential dependency:

1. We find in nature things that are possible to be and not to be, that come into being and go out of being i.e., contingent beings.
2. Assume that every being is a contingent being.
3. For each contingent being, there is a time it does not exist.
4. Therefore it is impossible for these always to exist.
5. Therefore there could have been a time when no things existed.
6. Therefore at that time there would have been nothing to bring the currently existing contingent beings into existence.
7. Therefore, nothing would be in existence now.
8. We have reached an absurd result from assuming that every being is a contingent being.
9. Therefore not every being is a contingent being.
10. Therefore some being exists of its own necessity, and does not receive its existence from another being, but rather causes them. This all men speak of as God.

Here, Aquinas rightly observes that there is a causal chain of events stretching from the present back to the big bang. This is an affirmation of determinism, a position I also agree with. However, he again assumes that the uncaused cause was necessarily intelligent. The only examples of intelligence we have so far encountered are all the result of evolution. Intelligence comes after a universe exists in which intelligence can arise, not before.

Moreover, to posit that a supernatural being exists because it is necessary according to your assumptions ignores the possibility that there exist unknown unknowns which would radically change your reasoning. In Aquinas' case, spontaneous particle pair separation events.

The fourth proof I have no problem with:

1. There is a gradation to be found in things: some are better or worse than others.
2. Predications of degree require reference to the “uttermost” case (e.g., a thing is said to be hotter according as it more nearly resembles that which is hottest).
3. The maximum in any genus is the cause of all in that genus.
4. Therefore there must also be something which is to all beings the cause of their being, goodness, and every other perfection; and this we call God.

Ignoring for a moment that there's no objective "better" or "worse", I agree fully that if you classify beings according to metrics like intelligence, the amount of power at their disposal and the like, there's necessarily one at the top of that hierarchy which far outclasses everything below it.

This is the supreme being I believe in, which I have written about before. But Aquinas looks for it in the wrong place, positioning it as something separate from and the creator of all existence, rather than one in the same with it.

That last point (#4.) also assumes that the capacity of every being is something deliberately given to it by the greatest being, which doesn't follow, though someone living in a feudal society might consider that logical.

The fifth proof is essentially creationism. It observes apparent design in living creatures and other natural phenomena:

1. We see that natural bodies work toward some goal, and do not do so by chance.
2. Most natural things lack knowledge.
3. But as an arrow reaches its target because it is directed by an archer, what lacks intelligence achieves goals by being directed by something intelligence.
4. Therefore some intelligent being exists by whom all natural things are directed to their end; and this being we call God.

Because Aquinas was ignorant of evolution, it must've seemed self-evident to him that you can only get design from an intelligent being, and this is why he assumed the first cause was intelligent. In particular he holds up the instincts of animals (such as the web building instinct of spiders, or the hive building instincts of bees) as proof of a creator.

However, now we know that isn't the case. Not only can evolution cultivate extremely complex instinctual behaviors, but the specific type of design found in nature is known to result from unintelligent naturally occurring optimizing processes like evolution, gravitational accretion and so on.

Perhaps the largest problem with his reasoning (though that's a close race) is that there's no way to get from these proofs to Christianity. Besides evolution fouling up his "proof" of the necessity of a creative intelligence to account for the complexity and behaviors of living organisms, the doctrinal claims of Christianity are a good deal more involved and less defensible than Aquinas' five proofs are able to bear out.

It could just as easily be used in support of Islam, for example. Or Mormonism. That's even before evolution was discovered. In light of it, the only elements of his proofs which still hold up more convincingly support a pantheistic deity than one which is canonically the engineer of the cosmos and all living things. That's to say nothing of how Yahweh is specifically male, one of the two human genders, and possessing all of the same preferences as the average man who lived during that era.