September 13, 2010

This Post is Old!

The post you are reading is years old and may not represent my current views. I started blogging around the time I first began to study philosophy, age 17. In my view, the point of philosophy is to expose our beliefs to rational scrutiny so we can revise them and get better beliefs that are more likely to be true. That's what I've been up to all these years, and this blog has been part of that process. For my latest thoughts, please see the front page.

What is Supposed to be Proved in Aquinas's Five Ways?

I'm not a Medieval scholar, so I don't really know what I'm talking about, but that's ok. Sobel's fifth chapter is concerned with Aquinas's Second Way, one of the classic texts for the cosmological argument. Sobel raises some concerns about the premises, but for the most part he finds them plausible (though he may ultimately reject one or more of them). His main concern is that, as he schematizes the argument, a fallacy of equivocation occurs at the very end. Sobel reads the 'good' part of the argument as (perhaps) justifying the 'Preliminary Conclusion':

(8) "[There is] a first cause among efficient causes" (ST I q2,a3 p. 22) - more fully, there is, for all sensible things that have efficient causes, a first cause that does not have an efficient cause and is not itself a sensible being. (p. 174, brackets and emphasis original)

This, Sobel says (pp. 190-192) is ambiguous between the claim, which he labels (8a), that for each sensible thing we may trace a causal chain backward to an uncaused first cause, and the claim (8b) that for any sensible thing, we may trace a causal chain backward to one and the same uncaused first cause. Sobel thinks that (8a) can be successfully demonstrated from Aquinas's plausible premises, but (8b) cannot. He also thinks that Aquinas uses (8b), plus the claim that everyone calls the first cause God, to demonstrate his ultimate conclusion, that God exists. So the equivocation between (8a) and (8b) is a serious error that undermines Aquinas's reasoning.

I want to suggest that Aquinas's intention was to demonstrate (8a) and stop there. Take a look at ST I q2,a2:

Reply to Objection 3. From effects not proportionate to the cause no perfect knowledge of that cause can be obtained. Yet from every effect the existence of the cause can be clearly demonstrated, and so we can demonstrate the existence of God from His effects; though from them we cannot perfectly know God as He is in His essence.

Aquinas here concedes to the objector that since we only observe finite effects we cannot, from them, prove de dicto the existence of an infinite being. But that, Aquinas says, does not mean that we cannot prove it de re. What I mean is this: we cannot prove the proposition that an infinite being exists. However, the fact that the cause is infinite does not prevent us from proving the proposition that the cause exists, thus we prove of the infinite cause that it exists.

When Aquinas takes up, in q3, the question "Whether God exists?", he is, I think, adopting this strategy. The line of thought is this: pick any sensible object you like. We can show that something, x, was the first cause of that object. Since the object exists, x must exist (or have existed). In fact (though we can't prove it) x is God.

This, I take it, is what Aquinas alludes to at the end of each Way when he writes:

this everyone understands to be God.
to which everyone gives the name God.
This all men speak of as God.
this we call God.
this being we call God.

Thus, as I read it, Aquinas's Second Way is meant to prove that, for any sensible object, there exists and uncaused first cause of that object and then assert without proof that ordinary uses of the name 'God' succeed in referring to that thing, and thus that God exists.

This reading might seem odd to us today, but I think it makes a lot of sense given how the beginning of ST is framed. In articles one and two, Aquinas frames the debate as one over whether the existence of God is provable or whether it is an article of faith. He concludes that the existence of God should in principle be provable, and only then asks the question "Whether God exists?" as a way of introducing proofs. From this perspective, the de re conclusion is to the point, insofar as, on this reading, Aquinas has proved the existence of something, and that something is (it is agreed by all parties to the debate) God.

(A concluding biographical note: this reading of the words "this all men speak of as God" and the related phrases was the one I came away with when I was first introduced to the Five Ways by the late James Ross, but I can't remember whether Ross endorsed it, or if it was just the way I read the text.)

Posted by Kenny at September 13, 2010 11:11 PM
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I believe this is the standard way Aquinas scholars take Aquinas. I don't know of any serious Aquinas scholars who disagree, but it's at least the majority view among analytic philosophers who write about Aquinas. He spends the rest of the philosophical theology section of the Summa arguing that the being referred to in the conclusion of the Five Ways arguments does have most of the traditional attributes Christians believe to be true of God, minus some key ones only knowable by revelation (e.g. Trinitarian and incarnational ones, for starters). So his argument that this is God is what he's about to argue, not what he takes himself to have argued already.

Posted by: Jeremy Pierce at September 20, 2010 12:46 PM

In that case, I wonder how Sobel managed to get so confused, or if he is just being uncharitable. Usually, he is pretty good at representing theistic arguments fairly.

Posted by: Kenny at September 20, 2010 12:54 PM

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