I rarely get involved in the so-called “method wars” of Christian apologetics. I think it’s largely unproductive to insist that our fellow brothers and sisters use a particular way of sharing the Gospel while we could be doing just that ourselves. I also think that, so long as the argument is valid and sound, that any Christian argument for God that brings someone to think about and consider Christianity is worthwhile. This is why I find value in the basic reasoning of presuppositional apologetic arguments. However, most of my readers will note that I tend to use a lot of evidential and classical arguments here. I’ve heard, more than one time, presuppositionalists insist that evidential arguments are detrimental to Christianity. The mission of this post is to suggest this is mistaken.
The argument goes like this: if presuppositional arguments are true, then evidential arguments for God are false. Why should we think a thing like that? Because, the reasoning goes, evidential/classical arguments only establish that the conclusion (namely, God exists) is only probable with respect to the evidence, not necessarily existent. Yet presuppositional arguments entail a necessarily existent God. Therefore, we have two fundamental types of claims that differ from one another in a major way. If God is necessary, it’s impossible for him to be contingent, and vice versa.
The problem in the reasoning in the above paragraph is one that runs rampant in the presuppositional community. I say what I am about to say not to attack, but to help. If we can help each other think clearer, it will be all the better for Christian apologetics! So what are the problems? I’ll try to tackle them from least important to most important.
First, in deductive arguments (and even some abductive ones), the conclusion is entailed by the premises. This means that if the premises are true, it is impossible that the conclusion is false. It’s somewhat of a category error to say the conclusion is “only probable.” However, this is considered the least important objection because we can still say that we are uncertain of the conclusion because we are not wholly (in a Cartesian way or something) certain of the premises’ truth. Second, in some cases (at least one) classical arguments do require that God be necessarily existent. The ontological family of arguments entails this, and some conceptions of the moral argument family do as well. Of course, the claim would still remain for all other types of arguments of whose premises we are not entirely certain.
Finally, the most important problem, and the one that runs rampant, is the confusion between ontology and epistemology. I attended an apologetics conference last year where a panel discussion took place on this idea, and the presuppositionalists were plagued with this issue. Ontology refers to being, or something’s existence. Epistemology refers to knowing, or knowledge/truth.
When the presuppositionalist complains that the conclusion of evidential/classical arguments is only probable, this is an epistemic category. It’s about knowledge, and degrees of certainty (in this case, not very certain). Necessary existence, which is established through presuppositional (and some classical) arguments, is an ontological category. The two are not exclusive. What is necessarily true is so independently of anyone’s even knowing it, much less anyone knowing it for certain. In fact, there are examples where we know that some proposition is actually necessarily true or necessarily false, but no one has any idea which. The point is that something can be necessarily true ontologically, but only probably true (or probably false, or even inscrutable) epistemologically. These evidential and classical arguments say nothing (most of the time) about the modality of the existence of God (contingent or necessary), and so it is an error to presume that they do.
Again, I’m still not interested in the method wars, where I insist that presuppositional reasoning be abandoned and only evidential/classical arguments used. I’m not interested in having a huge argument with my brothers. I’m just trying to sharpen our thinking, so that Christ’s Kingdom can be built, and he might have the preeminence.
 I speak of argument families here in recognition of the fact that there is no one, singular ontological or moral argument. The same goes for virtually every other type of theistic argument.