I want to start getting better about responding to podcast listeners via email on the blog, so…
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Pat,
I ask this because of your recent podcast on the kalam argument. I read an Aquinas commentator who explained that part of Aquinas’ reasoning in his third way goes as such: If all things that exist are contingent (possible not to exist) then given an infinite past, where all possibilities would occur, there would at some point have been nothing; and thus now be nothing. Couldn’t this same logic be applied as a reductio against an infinite past even if given the existence of a necessary being? If the past were infinite all possibilities would have occured and so whatever happens in the future would have already happened at some point in the past. This would lead to all sorts of absurdities, it seems, such as duplicate souls, for example. My birth is possible so I would have already been born before. I’m sure there are other absurd consequences. Does this line of reasoning hold up?
Thanks,
Don
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Dearest Don,
From, “every human being has a mother” it is wrong to infer that “someone is the mother of every human being,” because the quantifying term every has been erroneously shifted (Accordingly, the fallacy under consideration is called “quantifier shift.”) Think: just because every x is related to some Y, it does not mean there is some Y is related to every X. So, even if every contingent thing were related to non-existence (individually at some point); it wouldn’t follow that non-existence would (at once and collectively) be related to every contingent thing.
So, to answer your question, Don, I do not think this is an accurate interpretation of Aquinas, nor would I push this *specific* line of reasoning with respect to rebutting an infinite, backwards series of causes (or infinite past).
To the former point, Aquinas is generally brilliant, so I hesitate to embrace any interpretation of his 5 Ways in which he overlooks an otherwise basic fallacy. What’s more, I believe each of the 5 Ways must be interpreted in light of Aquinas’s existentialist metaphysics, as demonstrated in the De Ente. For my preferred interpretation of the 5 ways (including the 3rd), see my extended conversation with Dr. Gaven Kerr and Karlo Broussard, here.
As to the latter point, you are right about an actual infinite past leading to seemingly absurd consequences, though perhaps different from the ones you’ve identified. It is, of course, possible that no duplicate souls ever occur even within an infinite past, especially (and perhaps only) if God creates each human soul individually — for God could just create an infinite amount of unique souls, say. For the more pressing absurdities resulting from an actual infinite, I would see what Bill Craig has to say about Hilbert’s Hotel, etc, and then, see Feser’s rebuttal from presentism here.
Personally, I feel the presentism objection has force against some of the arguments Craig deploys, but that that objection can be sufficiently overcome with other arguments: ala Pruss and Koons.
– Pat
Pat,
Thanks for your reply! I don’t know how the first part of Aquinas’ argument in the third way is to be interpreted and I don’t want to misrepresent Aquinas so I’ll just speak of the “infinite past contingencies” argument (IPC). I don’t think IPC commits a quanitifier shift. IPC makes one crucial assumption: an infinite past involves the realization of all possibilities. (To quote Etienne Gilson: “Where there is infinite duration, it is unthinkable that a possib[ility] worthy of the name be not realized.”) So if P is possible, then (given an infinite past) P would have occured. IPC assumes one possibility (P) is the non-existence of all contingent things. I don’t see it as controversial or fallacious to claim that it is possible for all things that need not exist to (at once and collectively) not exist. I don’t see this as being an inference involving a quantifier shift but as taking into consideration possibility, contingency, and the nature of an infinite past. The alternative is that it’s not possible for all contingent things to (at once and collectively) not exist. I don’t see why this claim should be preferred over the alternative.
Hey Don,
Good stuff here. I’m familiar with that line of reasoning, as well, and while I think it is quite a plausible assumption (really, it certainly *seems* right, doesn’t it?), I don’t think it’ll rise to the level of demonstration, which Aquinas is after, since it’s at least broadly possible for one contingent thing to give way to another contingent thing, etc, ad infinitum, and however unlikely we feel such a situation may be, it’s an escape hatch that would need to be independently sealed off. Perhaps such an argument can be made, and, if so, I would be glad to hear it. Thoughts?
Pat,
In terms of arguing for a necessary being (since I can’t think of a way to disprove the possibility of one contingent thing giving way to another ad infinitum) I might agree. Not entirely sure because I don’t know who the burden of proof is on. But I still think “IPC” can be used within the kalam cosmological argument as a reductio against an infinite past since it would indicate that everything that is happening or will happen (and so being possible) has also already happened (since an infinite past would involve the realization of all possibilities).