If God does not exist, then it’s not the case that if I pray my prayers will be answered. I do not pray. Therefore God exists.
I came across this today in discussion of the paradoxes of material implication. The interpretation of the conditional ‘if I pray, my prayers will be answered’ is at issue. Is it equivalent to ‘either I won’t pray or my prayers will be answered’ or is there a more intimately conditional meaning? If the conditional is treated strictly conservatively and in accordance with classical logic, then the argument is valid. So the soundness turns on whether the premise is true. It looks plausible though, doesn’t it?