Did Aquinas’ arguments just suck?

I’ve been rethinking this post, where I suggested part of the reason the arguments of people like Thomas Aquinas and Samuel Clarke don’t sound convincing today is that they use assumptions which used to be widely accepted, but aren’t anymore. I offered up some caveats about that suggestion at the time, but now I have even more doubts about it.

What prompted this is Leah Libresco’s complaint that the example from Aquinas I used in the previous post only sounds unappealing to modern ears because of Aquinas’ jargon, and if you explained the jargon it would be more appealing. So I went looking for a way to make my original point with a relatively jargon-free example, and found Aquinas’ arguments for the impossibility of an infinite regress of causes (important, because that plays a role in three of his Five Ways):

[13] Furthermore, that it is impossible for the abovementioned infinites to be moved in a finite time Aristotle proves as follows. The mover and the thing moved must exist simultaneously. This Aristotle proves by induction in the various species of motion. But bodies cannot be simultaneous except through continuity or contiguity. Now, since, as has been proved, all the aforementioned movers and. things moved are bodies, they must constitute by continuity or contiguity a sort of single mobile. In this way, one infinite is moved in a finite time. This is impossible, as is proved in the Physics [VII, 1].

[14] The second argument proving the same conclusion is the following. In an ordered series of movers and things moved (this is a series in which one is moved by another according to an order), it is necessarily the fact that, when the first mover is removed or ceases to move, no other mover will move or be moved. For the first mover is the cause of motion for all the others. But, if there are movers and things moved following an order to infinity, there will be no first mover, but all would be as intermediate movers. Therefore, none of the others will be able to be moved, and thus nothing in the world will be moved.

[15] The third proof comes to the same conclusion, except that, by beginning with the superior, it has a reversed order. It is as follows. That which moves as an instrumental cause cannot move unless there be a principal moving cause. But, if we proceed to infinity among movers and things moved, all movers will be as instrumental causes, because they will be moved movers and there will be nothing as a principal mover. Therefore, nothing will be moved.

Now, there are a couple little things that might need explaining here. It’s often said that the word translated here as “move” should be translated “change,” and it’s worth noting that in the first argument, Aquinas appears to assume causes that are simultaneous with their effects. Even with that in mind, though, these arguments look pretty bad.

In the case of the first argument, sure it may seem impossible for one thing to undergo an infinite amount of change in a finite amount of time, but I don’t see any reason why that would mean that an infinite number of things can’t all change simultaneously.

In the case of the second argument, I don’t see how the fact that taking a way the first cause in a finite chain proves that a first cause is in any way special. After all, remove a cause somewhere in the middle of a causal chain, and that also eliminates anything causally downstream of it. That gives you the analogous fact about an infinitely long causal chain, not that the infinite chain would need a first cause too.

And the third argument is just a variation on the second one, and the problem is basically the same. I just don’t see any reason to accept the first premise of the argument.

Now, the broad point here is that while these arguments are supposedly derived from Aristotle, there doesn’t seem to be some secret Aristotelian assumption that would make them work. They’re just plain old bad arguments. I feel comfortable saying this, because respected living philosophers often give arguments that just stink, and being a contemporary of those philosophers I’m confident that the issue isn’t some peculiarly 21st century assumption.

In fact, Aquinas’ arguments feel very similar in their style of badness to William Lane Craig’s bad arguments against the possibility of an infinite past that go into Kalam. Or anyways, that’s true aside from the fact that set theory didn’t exist in Aquinas’ day and therefore he couldn’t get into arguments over its significance.

  • http://deusdiapente.blogspot.com J. Quinton

    A lot of “bad” philosophical arguments are based on intuition, which itself is based on the multitude of biases and heuristics that the brain has. Of course those biases aren’t meant for a priori truth finding modules, but for not ending up dead.

    • Chris Hallquist

      A lot of mediocre philosophically arguments are based on intuition. Where a lot of the really awful ones come in, I think, is when someone realizes not everyone shares their intuition, and they do a lot of foot stomping and handwaving to prove those other people are poopy-heads.

      • http://theaunicornist.com Mike D

        Wait… so you’re saying that William Lane Craig’s Kalam argument, based on “the metaphysical intuition that something cannot come from nothing” isn’t a totally airtight argument?

  • smrnda

    A big problem with Aquinas is that he’s talking about the physical universe and drawing conclusions based on reasoning from basic premises and intuition, a job that we use scientists and the experimentation for these days.

    Recall a discussion I had with a fan of Aquinas about homosexuality on a blog where he kept arguing it was wrong based on notions of ‘directedness’ and ‘wholeness’ and ‘Being’ with a capital B and stuff. Whenever I asked for a translation of the jargon, I just got more jargon, and then more when I asked for that because Aquinas is throwing around a bunch of vague words to form the basis for a philosophy as if they had a precise meaning.

  • http://quinesqueue.blogspot.com Quine

    Aquinas comes up, often, in my discussions with religious people, especially Catholics. I like to ask them things like, “How would Aquinas have figured that if he had the use of <a href="http://plato.stanford.edu/entries/continuity/"infinitesimals that we now do in Calculus, and how would he have reconciled that with Quantum Mechanics at the tiniest scales?” or “What would Aquinas have said if he found out that the moon is going in a” straight line through warped space-time?” Of course, the big one is to ask what Aquinas would have made of the fact that we evolved from a common ancestor with apes over the last 6 million years, and that our thoughts are made by biochemical processes in our brains?

    I am not asking to get any specific answer, but to get them to see that no matter how smart Aquinas was, he had to work from what was know about the world and our place in it during his time. One of the hardest things that philosophers have had to let go of is the idea that “nothing” or emptiness on the quantum scale does not, from empirical testing, seem to match the idea of the empty box that goes back back in human thought as far as you want to look. The “nothing” that no thing can come from does not appear to exist. I would love to be able to ask Aquinas about that one.

    • eric

      I think this is a good point. Reading (13) you can tick off the errors: infinity wrong (mathematically convervent infinite series), simultaneity wrong (relativity), contiguity wrong (QM). But the guy lived in the 1200′s, so its a bit unfair to bash him for this.
      Yes, they’re lousy arguments. They are as credible to modern physics and philosophy as humors are to medicine. However, students should also understand that this doesn’t mean we think Aquinas was an idiot. He tried to come up with hypotheses given the background knowledge available at the time.

  • JHendrix

    I have to wonder, even if we accepted Aquinas’s theories of the unmoved mover, why would we have to postulate that it’s something supernatural?

    Given modern science, cosmology in particular, the idea of our space-time universe coming into existence from a quantum nucleation event (ala Krauss or Vilenkin) is our best theory on our origins.

    So instead of “god” just existing necessarily, you have some form of energy existing necessarily, whose nature involves oscillation between potentials. The difference is that the quantum theory isn’t anthropomorphized into a personality like god is.

    • eric

      Not even energy, just something like what we call a law of nature which allows energy to come into existence. So no, nothing ‘supernatural’ needed.
      The unmoved mover could just as easily be the Heisenberg Uncertainty Principle as it could be God. And any rational person, considering two or more choices of hypothetical unmoved mover, should prefer the hypothesis that has the best evidence of existence.

  • qbsmd

    I once saw someone claim that “unmoved mover” makes sense if “move” is taken to literally mean move, not change, given Aristotle’s pre-Newtonian ideas about motion. Aristotle believed, for example, that an object thrown into the air was given an “impetus”, and would move in a straight line, until the “impetus” ran out and it would fall straight down. If you take that to its natural conclusion, then everything should stop after some amount of time when all of the impetus in the universe runs out. Since Aquinas didn’t observe motion to be slowing or wearing out, he naturally assumed something was actively giving everything a continuous push. After replacing Aristotelian mechanics with modern physics, like forces, accelerations, and potential and kinetic energy, I think it would be fair to conclude that Aquinas’ god in that proof was the nuclear fusion that powers stars.

  • abb3w

    It looks like he’s neglecting the resolution of Xeno’s Paradox (an infinite series may have a bounded sum), and neglecting the possibility of an (at least partially, perhaps totally) ordered set without lower bound (EG: the integers, rationals, or reals). That is, he assumes all orderings on sets must have a first element, which is not the case (even without cracking out affirmation-vs-refutation on the Axiom of Choice). As happens, time appears to map poorly to integers, in that the Big Bang seems to provide a lower bound. However, that’s not a philosophical necessity.

    I’ll note in passing, Anselm’s Ontological proof similarly runs into problems with posets (an upper bound may only be outside the set, or simply not exist at all). Little wonder Bertrand Russell ended up an atheist/agnostic.

    • smrnda

      This is probably why Beka Books does not believe in Set Theory.

  • Nox

    I’d say your initial assessment was closer. It’s not that Aquinas’ arguments just suck. It’s that they are based on premises which are now known to be untrue (and which those using Aquinas in a modern context would probably rather not think about). Thomas Aquinas applied the best reasoning of he 13th Century to the best data from the 13th Century, and created a set of arguments which could have seemed perfectly sound…in the 13th Century.

  • http://skepticgriggsy.wordpress.comhttp://skepticity.blogspot.com Lord Griggs[ IgnosticMorgan,InquiringLynn,Fr. or Rabbi Griggs, CarneadesofGa]

    His fourth one, his ontological one, reifies the continum of degrees of qualites as God. In “Primary Philosophy,” Michael Scriven counts it as nothing, letting his readers come up with their own solution.

  • http://skepticgriggsy.wordpress.comhttp://skepticity.blogspot.com Lord Griggs[ IgnosticMorgan,InquiringLynn,Fr. or Rabbi Griggs, CarneadesofGa]

    And his superfluity argument that none should add God as the ultimate explanation boomerangs on him with his five failed arguments!

  • Pingback: Ed Feser, physics, and the Dunning-Kruger effect


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