A few weeks ago I posted my argument against any and all a posteriori arguments. I thought I would revisit the argument again today and try to spell it out more clearly and concisely.
By a posteriori argument, I merely mean any argument that seeks to disprove God’s existence on the basis of some fact of the world, be it evil, evolution, “divine hiddenness”, the success of the natural sciences, or the failure of mind/body dualism. These arguments essentially boil down to something like:
1. If God exists, we would expect to observe X.
2. X is not the case.
3. Therefore, God does not exist.
The argument is in the form of a modus tollens deduction, which is a perfectly valid form of argumentation. My response is a kind of dilemma that puts the atheist in the awkward position of defending the soundness of the argument. I contend that any successful defense of the soundness of such arguments requires one to commit an informal fallacy of begging the question.
But first I think it is important to unpack my concept of God. I believe God is the greatest conceivable being, a definition common to classical theism. Here, Dr. William Lane Craig discusses this concept of God, and its implications. I would agree with what he says:
Dr. Craig points that since God is conceived of as a necessary being, if God possibly exists, then God actually exists. Now my argument is much more humble than this, as I do not even suppose that God’s existence is logically possible. What I offer is the following dilemma:
1. If the a posteriori argument is to be sound, then the truth of the conditional premise must be based on appeals to possibility or impossibility.
2. If the truth of the conditional premise is supported on the grounds of possibility, then there must be a possible world where the antecedent and consequent obtain, be it a fact of the actual world or counterfactually.
3. If God’s existence possibly obtains, then God actually exists.
4. If God actually exists, then either the first or second premise of the a posteriori argument must be false and the argument unsound.
5. If the truth of the conditional premise is supported on the ground of impossibility, then there is no possible world where the antecedent obtains and this counterpossible conditional is trivially true.
6. If the conditional premise is true because it is a counterpossible conditional, then the support for the first premise is nothing more than the assumption of the conclusion, which is to beg the question.
7. Therefore, either the a posteriori argument is unsound or question-begging.
Now one might challenge my argument by saying that the atheist need not assume that God is possible or impossible at the outset. However, if the argument is to be any good, the atheist must provide reasons that compel her interlocutor to think there is epistemic warrant for accepting the truth of the premises. After all, the conditional premise might be false. If the atheist draws out implications from the concept of God, then we must ask how it could be that the concept of God supplies those implications. The atheist is limited here. She cannot admit that the implications are drawn from a coherent conceptual analysis of God, since this would suggest that in at least one possible world where God exists and such implications follow. That would mean that God is logically possible, and so actual. Thus, the only alternative is that the implication is drawn out of an incoherent or impossible concept. But then anything could be said to be implied by the impossible, so the implication is merely a trivial one. The atheist would have to admit that “If God exists, gratuitous evil would not exist” is just as true as “If God exists, light bulbs wouldn’t exist”. If that is all the atheist is saying, then the argument is no more interesting than its theistic cousin “Either God exists, or 2+2 is 5, and since 2+2 is not 5, God exists.” More to the point, if the conditional premise is trivially true because it is counterpossible, then the atheist’s argument is simply fallacious. Clearly the atheist intends to disprove God on a posteriori concerns, but she ends up appealing to the impossibility of God, a priori, as epistemic warrant for the truth of the conditional premise. Since no argument is given for the impossibility of God, and it is just smuggled into the first premise, this is textbook question-begging.
Let’s suppose that the atheist admits this much, but then claims that she will back up her a priori assumption that God is impossible by way of an argument. But then she is arguing about God’s existence purely on a priori concerns, and that is not the original argument offered at all. So, I think this adequately demonstrates that the atheist is limited to presenting a priori arguments in favor of that position and that a posteriori arguments are useless in disproving God’s existence.