Apologists who seek to defend their faith in this manner have apparently lost sight of what their own worldview explicitly affirms. Within the context of the Christian worldview, the attempt to “argue from the impossibility of the contrary” would ultimately be self-refuting. And here's why.
Christianity’s positions are based on what is written in the bible, and the bible claims that “with God all things are possible” (Mt. 19:26; emphasis addedd). Now, that’s what the ‘good book’ says. I didn’t write it, so don’t get sore at me for what it says. The point here is that, if the believer claims that some particular thing is impossible, then he is blatantly disagreeing with what is explicitly stated in the bible. Since the presuppositionalist wants to defend his Christian faith-beliefs on the basis of what he calls “the impossibility of the contrary,” he’s clearly assuming that something is impossible, and this does not square with what the bible explicitly teaches. So this aspect of the “presuppositional method” of apologetics is in its entirety inconsistent with the worldview that it is intended to defend. For this apologetic strategy to have any force, it must borrow from a rival worldview which does not teach that “all things are possible,” and yet it is precisely such a worldview which the “presuppositional method” claims is impossible. Thus, such a strategy is, within the context of the worldview it hopes to protect, completely self-refuting.
The problem gets even worse for the presuppositionalist. Given what is clearly and unmistakably affirmed in Matt. 19:26, the believer must accept as a possibility any worldview which rejects primitive worldviews like Christianity. If one accepts the view that “with God all things are possible,” then he would have to accept along with this the supposition that it is possible that this god has created viable worldviews which do not acknowledge his existence. Indeed, if this god is both omnipotent and infallible, who’s to say it could not create in such a manner? All this is to say that, on Christianity's premises, there is no such thing as an "impossibility of the contrary." Thus for the presuppositionalist to want to "argue from the impossibility of the contrary," he must abandon his Christian presuppositions and seek a compatible theory of possibility in some worldview which he has already said is impossible.
Now surely the apologist is going to want to squirm out of this agonizing pinch somehow. To do this, he’ll probably want to say that I’m taking Matthew 19:26 out of context. After all, this is the verse that he's going to have to deal with one way or another. So if he takes this course, we must ask: what is the context that I’m leaving out of my interpretation? The verse does say what it says, does it not? Reading through the passage will quickly show that the context here is rather thin to begin with. The statement in Matt. 19:26 is the answer that the gospel writer puts into Jesus’ mouth in response to a question asked by the disciples in the previous verse: “Who then can be saved?” As is typical of the Jesus of the gospels, no specific answer is given. (I'm reminded of Luke 23:3, where Pilate asks "Art thou the King of the Jews?" and Jesus' very informative answer was "Thou sayest it.") Rather, the question, which I would think is of great importance to believers interested in who gets to be “saved,” is answered as vaguely as possible. So again, what context is being overlooked here? Blank out.
The apologist might say something like, “Jesus didn’t meant that everything is possible. That would be absurd!” Well, who’s disagreeing with the fact that Christianity is absurd? The Christian apologist apparently is, and yet he has to adopt a rival worldview’s premises in constructing an apologetic method which says that rival worldviews are impossible.
To settle the matter, the apologist merely needs to state whether or not he agrees with the statement that “all things are possible,” and then we can see whether or not he is willing to argue in a manner that is consistent with what the bible explicitly states. If he says “yes, I agree with Matthew 19:26 in that ‘all things are possible’,” then he concedes that “arguing from the impossibility of the contrary” is anathema to Christianity’s own premises. If he says “no, I don’t think it’s true that ‘all things are possible’,” then he simply disagrees with what the bible explicitly states and concedes that he borrows his conception of what is and is not possible from a non-Christian worldview in order to assemble his defense of the Christian worldview, thus refuting himself.
No doubt apologists confronted with these points will spit and stammer in their desperation to protect their commitment to a faith-based worldview from internal critiques of this sort. But basically the only hope for escape is essentially to claim “that’s what it says, but that’s not what it means” and hope it succeeds in snowing people. And though he may succeed in convincing himself that there’s no problem here, others will not be so easily fooled.
by Dawson Bethrick