The last post was about counterpossible conditionals as applied to questions about moral rules and "ought implies can." It occurs to me that there's another obvious application of such conditionals, in arguments for atheism.
As is (for better or for worse) standard for discussions about God in analytic philosophy of religion, I'll assume that by "God" we mean an entity that combines the three properties of omnipotence, omniscience and omnibenevolence. There seem to me to be two excellent arguments against the existence of such an entity...one from the "Stone Paradox" and one from the problem of evil.
Start with the "Stone Paradox," taken from the classical formulation about stones too heavy for God to lift. (My favorite formulation of it is, of course, the Simpsons version: "Could Jesus microwave a burrito so hot that he himself could not eat it?") If you say that there are no limits to what God can do, you certainly can't turn around and say that He can't make a stone of a certain level of heaviness. If you say "but there is no such level of heaviness!", you've just abandoned the original premise that God is omnipotent....surely, an omnipotent being can make stones as heavy, burritos as hot, as He likes.
The Stone Paradox for omnipotence seems to exact structurally parallel Russell's Paradox for unrestricted comprehension in naive set theory. If the latter shows either that naive set theory is a hopelessly inconsistent theory that must be abandoned (as the orthodox story goes, although I'm sure that some readers of the blog would beg to differ with the "must be abandoned" part), then the Stone Paradox shows the same about the theory that something is omnipotent.* In both cases, ad hoc restrictions to save consistency--"well, maybe for every *logically possible* property, there's a set of things that have that property....", etc.--fall pretty flat.
The second excellent argument against the existence of God** is the argument from evil. A being that was omniscient would know about the Holocaust, one that was omnipotent would have it in His power to send bolts of lightning down onto the train tracks leading to Auschwitz, and one that was omnibenevolent would certainly want to do so. The structure of the argument looks pretty clear: If God existed, gratuitous evil wouldn't exist, but it does exist, so God doesn't.
The various traditional defenses all, it seems to me, fail pretty spectacularly. Many of them are morally repugnant on their face, some of them seem obviously inapplicable to natural evil, or rest on un-argued and non-obvious assumptions about the nature of good and evil, or on strange accounts of free will that seem to go well beyond the most wild-eyed libertarian accounts out there, or in some other way seem implausible on their face. Even the ones that seem establish that X wouldn't exist without evil and X is a good thing never come even close to clearing the bar of showing that both (a) X is more good that Auschwitz, etc., are bad, so that the trade is worth it, and (b) in order to have X, we need anything even close to *as much* suffering as in fact exists. To anyone who's ever taken an Intro to Philosophy class, the details of this argument are fairly familiar, so, if you agree with me about this, you're the one I'm talking to, and we'll move on from here.***
So, both of the major, classical, historically influential arguments from atheism mentioned here seem to be good ones.
The formulation of the argument from evil necessarily involves a counterfactual premise..."If God existed, then such-and-such would be the case."
But earlier, didn't we establish that it's not logically possible that God could exist?****
So, if you understand counterfactuals in the Lewissian way, in terms of truth-preservation over the closest *possible* worlds in which the antecedent is true, then that conditional is completely trivial, since there are no possible worlds in which God exists. "If God existed, then everything would be exactly the way that it is now" and "if God existed, there would be a planet full of unicorns" would have precisely the same status as "if God existed, then gratuitous evil would not exist." That doesn't seem to be the case. That last conditional seems to be clearly, importantly and non-trivially true. Some one who is talked out of theism by the argument with that conditional as its first premise, far from being taken to have been irrationally suckered in by a silly argument from something trivial, should be praised for having taken a long stride in the direction of rationality.*****
If that's true, you'd better be willing to extend your logic to include a non-trivial counterpossible conditional connective, and, if you have a possible-worlds analysis of counterfactuals, you'd better be willing to entertain impossible worlds as well.
*Small prediction, BTW...someone correct me if I'm wrong here...but to the best of my knowledge, there aren't any Christian Dialetheists yet, but sooner or later, there will be. I'm sure that somewhere down the line young theist grad student interested in formal logic at Notre Dame, too honest to deny the contradictions entailed by his theology, will have a light bulb go off over his head during a phil of logic seminar, and decide to marry the teachings of Thomas Aquinas and Graham Priest.
**Remember, we're talking about the traditional omni-omni-omni God here. The average northern college town Episcopal Priest or Reform Rabbi would describe the object of their worship in a much different way. Whether any such liberal theologies are themselves plausible or not is an entirely different subject.
***If you don't agree with me, I'd be happy to follow up in the comments section, but right now, for the sake of making the logical point being built up to, I'm just gesturing at the atheistic arguments, and trying to make my case (about conditionals) to those who already accept them.
****Hey there, future Christian Dialetheists going back to read this blog post from 2009 predicting your existence! Say hi to everyone in the future for me!
*****Of course, you might be tempted to say something like the following. 'Look, given the paradoxes of omnipotence, that conditional is trivial, but it's a useful second-level-of-attack, since *if* those paradoxes could be satisfactorily solved, then the argument from evil would be an excellent objection to theism.' To which I'd have to reply, 'OK, but dude, given your assumptions, that itself was a counterpossible conditional! There's no escaping them.'