The below was posted by my philosopher friend, Shane Wilkins, in the course of comments on a recent post by my friend and collegue David Congdon. Get the original post and the comment thread here. It seemed to me that Shane's comment was too rigorous for me to allow it to languish somewhere in a comments thread, so I asked his permission to give it a permanent home here at DET. It deals with, among other things; proving the existence of God, natural theology, Barth and Thomas. And so, without further ado, I give you Shane Wilkins on 'whether it is provable that God exists.'
Thanks to Chris, David and KF for interesting responses. I think there may be a bit of confusion regarding what precisely I am saying, so I'll give it another go. I'm not so worried about Barth at the moment, so if someone tells me I've misunderstood him, that's fine. I'm more concerned with a constructive case I'm trying to make.
The first thing I want to point out is the difference between a proposition "p" and the proposition "p is provable".
There are four possible relations between "provable" and "p":
1. "p" is true and provably true.
2. "p" is true but not-provably true.
3. "p" is false and provably false.
4. "p" is false but no-provably false.
(establishing 2 and 4 in the logical language of arithmetic is the goal of Gödel's Second Incompleteness theorem. NB: if p is provable, then it is true and if p is disprovable then it is false.)
Now, let's take the proposition "God exists". It is necessary in order for a person to be a Christian that believe this proposition is true. But note that I am not saying that one must believe that this proposition is provable to be true to be a Christian. So you can affirm "God exists" according to either (1) or (2) above.
But is it provable or disprovable that God exists? (Pace Chris we aren't talking about pragmatics here, because we are just assuming that if there is a true argument demonstrating the existence of God, then it will be successful in the pragmatic sense, but its truth doesn't come from the fact that it is persuasive to people, rather the other way around.) All I can say is that it is clear that nobody has put forward a completely successful proof or disproof of God's existences in the 2500 odd years of philosophical reflection, although there are certainly some very suggestive results in both directions. A pessimist might take this problem as insoluble just because of its longevity, but that's just the coward's way out. "Everything fine is difficult" as the Greeks say and certainly the history of mathematics tells us of
"http://mathworld.wolfram.com/GeometricProblemsofAntiquity.html">seemingly insoluble problems which are somehow resolved centuries after they are proposed.
Of course, as David rightly points out, this all depends on what we mean by "God" (and this also bears on the meaning of the term 'natural theology'). Now I take 'natural theology' to mean that subsection of metaphysics which investigates God rationally. It is this mode of investigation which distinguishes natural theology from revealed theology where God is investigated on the basis of supernatural revelation. David says that whatever a natural theologian might prove about God can have no purchase on the God of Jesus Christ. This response attempts to draw a divide between philosophy and theology, leaving the secular pursuit of philosophy intact, but denying its significance for (revealed) theology.
My disagreement comes back to the definition of "God" in the proposition "God exists". I take "God" to point to an infinite, perfect, necessarily existent being who is simple, good, omnipotent, omniscient, transcendent, benevolent, impassible, etc.
Now suppose (just for the sake of argument) that I create an argument that proves such a being to exist. From this I can prove that there is exactly one such being.
(A perfect being must possess all attributes that would make it good and must possess no attributes that would make it bad. It is impossible to suppose that two such beings exist because there could be no attribute which they would not share. If perfect-being-1 possessed A and A is a perfection that perfect-being-2 lacks, then perfect-being-2 is not perfect, contrary to our assumption. Therefore, by the identity of indiscernables there is at most one perfect being. This argument is blatantly stolen from Thomas.)
If I have proven logically that there exists at most one perfect being and that such a being actually does exist, then I am talking about the only God who exists whom I also believe the basis of revelation to be incarnate in Christ. It is the same God who is spoken of in both my logical argument and the creeds of the church.
What value does natural theology have for revealed theology? Well the proof of the pudding is in the eating. To really answer this question, you'd have to spend a lot of time looking at dogmatic theologians who were also natural theologians and trying to sift out where the ideas came from and how they are interrelated in his work. My suspicion is that you aren't going to find anybody on this side of the enlightenment who has engaged in this kind of enterprise, so it may be that we need to make a retrieval of some parts of the pre-critical Christian heritage to find out how to do this well. So I think we in the 21st century still have a lot of work to do before we can really try to answer this question well.
Now, to respond to Kim, I don't think we ought to postulate a God of the gaps, but the problem with the "god of the gaps" idea is that it presupposes that science is limitless, boundless, will eventually explain everything that is in need of explanation, etc. The danger of the god of the gaps strategy is that your gaps threaten to shrink. But, I am convinced that there are significant "gaps" which empirical science can never penetrate. "Why is there something rather than nothing?" If a guy in a labcoat tells you he has a solution to that question, slap him and tell him to get back to his test-tubes. God is a good solution to that problem and we don't need to worry about science somehow providing a superior explanation in the future.
Now, with regard to Thomas. I simply cannot see what Rogers can mean. Thomas believes that the existence of God (with a big G) can be proven a posteriori through creatures (ST 1a, q. 2, a. 1). I find it hard to believe that Thomas would say that only a believer could know that God exists because each of his "five ways" are taken from a passage in Aristotle. (Argument from motion in Physics VIII, also look at the Metaphysics XII). I just don't see any harmony between Thomas and Barth on this point.
Now it is true that Thomas thinks that all knowledge we have comes by grace to some extent, but this is also clearly different from what Barth would say. Perhaps Rogers means that nobody could learn God's existence for Thomas apart from natural grace, but I'm not sure what the point of saying such a thing would be. And it seems clear to me that Barth would be tremendously unhappy with people learning things about God from creatures on the basis of natural grace.