Part of the spillover of the Trinity debate is into the area of natural theology. The tension between presuppositionalism and classic apologetics that R. C. Sproul insisted on maintaining and is now being maintained by J. V. Fesko has to do with that. Classical Theism requires natural theology, and attempts to deny it are going to continue from presuppositionalists because that is predicated on the hard rejection of natural theology. I haven’t gotten into the debate and am the last person anybody should consult on apologetics, but I understand the difference to be thus.
The approach of classical apologetics is to address the atheist and the agnostic in terms of natural revelation and natural theology. The atheist has to be refuted, the agnostic persuaded of theism. But not on the grounds of special revelation. They can be reasoned with using general revelation. One can use the five ways to demonstrate that there can’t not be a God. The second step of classical apologetics is to use the evidence of special revelation for Christian theism as the only true alternative. It is where the evidentialist begins, so that the difference is that the evidentialist always begins here, and the classical apologist finds the toolkit the evidentialist uses unnecessarily limited. (I wonder if the evidentialists don’t confuse clarity with authority, and on those grounds dismiss the theology of natural revelation. But I don’t know, apologetics only being an interest of mine in the effort to get away from the presuppositionalism which annoys me.)
Presuppositionalism rejects both natural theology and evidentialism. It is about affirming a perspective, the perspective that presupposes God, and then shows that no other perspective is adequate. I don’t think this is an approach so much calculated to persuade as to assume its triumph merely. I find presuppositionalism disagreeable to me for two reasons: one is that it has always struck me as condescending to any position that doesn’t share its perspective, especially pagans and, alas, C. S. Lewis; the second is that it works too much like an ideology.
An academic discipline, Roger Scruton has somewhere said, is a set of questions. In order to master that discipline you master a set of questions, and the conversation that has resulted in search of answers. Because the questions are fundamental in nature, and because the answers they seek are not simple, there is an openness to an academic discipline, a development and also something constantly unfinished about it. It is an exploration that could continue indefinitely. Of course, it develops a substantial body in the ensuing conversation, but there is room for the conversation to continue down through the ages. An ideology, on the other hand, is a set of answers. It masquerades as an academic discipline but is not really inquiring and not fundamentally honest.
An academic discipline can be hijacked to a lesser or greater degree by something like an ideology or on the way to ideology. For example, you can ask a historical question and then limit the answers to those which contain women. You can still get accurate history, but you are limiting the discipline. That has a very limited usefulness, and is more of a way of sorting results, assuming you have achieved a meaningful result. An ideology is when you pretend that the only valid questions are the ones whose answers only contain, for example, women, or mostly women. To the degree that you control by means of the answers, you are being ideological.
Presuppositionalism is perspectival. It is one of these worldview things. A pox on worldviews! Perspectives tend to limit the answers. They are used under a guise of humility, like sheep’s clothing, but they are about controlling more by answers than by proper questions and the diligent integrity of the conversation. The open-endedness of something controlled by the search for honest answers is unwelcome to the ideological mind. And what presuppositionalism does must be that way if you foreground the noetic effects of sin so that natural theology is altogether impossible.
I think the problem there is that the noetic effects of sin, while distinguishable from the moral effects of sin, are not separable and not quite as preponderant as presuppositionalism makes them out to be. What hinders a person’s mind from grasping natural revelation? A lack of truth is caused by a lack of honesty, which is a lack of integrity, which is a matter of the heart. A lack of truth may be cause by a lack of boldness, by a refusal to persist in some adversity because it is right to persist. Persistence is courage, and clarity of mind requires courage. Courage has the word heart in it! Courage is moral. So moral that God says that all cowards will burn in hell, and hence so noetic that the Rabbis said that the timid student will never learn. But there are degrees of integrity and certainly of courage in the unconverted. So, they achieve partial degrees of knowledge of God by natural theology. Of course, they need the second step that the evidentialists are so good at, because natural revelation is only adequate for establishing theism.
What I find that the present debate has established clearly for me is that without natural theology you will struggle to have a proper grasp on Classic Theism. Natural revelation is not as clear as special revelation in terms of redemption, but it is authoritative. Authority, after all, depends on the source. Treat it otherwise and you will have a problem with God.