The Witness of the Spirit as an Intrinsic Defeater-Defeater
Dear Dr Craig
I am sometimes worried by the assertion you make that, even if all your arguments for God's existence were disproved, you would continue to have faith because of the witness to the Holy Spirit.
Does that mean that if any or all of the following:
1. The universe was discovered to be eternal
2. The fine-tuning was given a natural law
3. Morality was merely a socio-evolutionary tool
4. The gospels were discovered to be unreliable, or that Jesus' bones were found (remember the apostle Paul saying that if Jesus is not risen, Christians of all men are to be pitied)
...were proven true, you would continue to be a Christian in the face of the evidence?
The reason I ask is that this assertion seems to undermine your apologetic efforts sometimes. Remember Christopher Hitchens pointing this out in your debate, or John Humphreys asking if you would still have faith if Lewis Wolpert had defeated your arguments?
Lastly, and most crucially of all, if you are entitled to have faith, even if the evidence is against you, then why debate Muslims? Couldn't they just say that their faith in Allah will see them through the "shifting sands of evidence"?
Let's be careful to formulate correctly the claim you ascribe to me, Peter. What I claim is that for the person who attends to it the witness of the Holy Spirit overwhelms the putative defeaters brought against the truths to which He bears witness. Alvin Plantinga calls such a powerfully warranted claim an intrinsic defeater-defeater because it defeats all on its own the conflicting claims brought against it.
Now this is importantly different from speculating about what I would do in such circumstances as you describe. I have no idea what, given the weakness of my flesh, I actually would do; but I know what I should do. I should attend to the witness of the Holy Spirit. But far be it from be me to say brashly with Peter, "Even though they all fall away, I will not!" (Mk 14.28). So I am not asserting so strong a claim as you ascribe to me.
On the other hand, I am asserting an even stronger claim that you attribute to me. For not only should I continue to have faith in God on the basis of the Spirit's witness even if all the arguments for His existence were refuted, but I should continue to have faith in God even in the face of objections which I cannot at that time answer. The first claim is not really all that radical: I think most theologians, not to mention ordinary believers, would say that arguments of natural theology are not necessary in order for faith in God to be rational. In the absence of some argument for the truth of atheism, I can be perfectly rational to believe in God on the basis of the Spirit's witness.
What I'm claiming is that even in the face of evidence against God which we cannot refute, we ought to believe in God on the basis of His Spirit's witness. Apostasy is never the rational obligation of any believer, nor is blasphemy against the Holy Spirit. God can be trusted to provide such powerful warrant for the great truths of the Gospel that we will never be rationally obliged to reject or desert Him.
So to, address your specific scenarios:
1. If the universe were discovered to be eternal, we'd be obliged to give up biblical inerrancy (as well as the kalam cosmological argument), since the Bible teaches that the universe was created a finite time ago. But obviously, that wouldn't imply that God does not exist or that Jesus didn't rise from the dead.
2. If the fine-tuning were shown to be the result of natural law, then one would have to give up the argument for a designer based on the fine-tuning of the universe. One could still run an argument for design, as Robin Collins does, based on the beauty and precision of nature's laws, if not on the values of nature's constants and quantities. Obviously, once more, even the utter failure of any design argument wouldn't be a positive proof that God does not exist.
3. If it were proven that morality were merely a socio-evolutionary tool, then theism would be false and there would then be no witness of the Holy Spirit, since God would not exist. For theism entails that objective moral values and duties exist. So if they didn't, theism would obviously be false. The key here is the word "merely." We can agree that the way in which we come to know moral values and duties is through the evolutionary process, but to conclude that they are therefore not objectively real would be to commit the genetic fallacy of trying to invalidate a view by showing how someone came to hold it. Absent a proof of atheism, the socio-evolutionary account of our moral beliefs does nothing to negate their objective validity.
4. Again, if Jesus' bones were actually found, then the doctrine of his resurrection would be false and so Christianity would not be true and there would be no witness of the Holy Spirit. So if Jesus' bones were found, no one should be a Christian. Fortunately, there is a witness of the Holy Spirit, and so it follows logically that Jesus' bones will not be found.
As to your point about my defense of the witness of the Spirit undermining my apologetic efforts, I have no choice but to hold to the religious epistemology that I think is true, whatever the consequences. Ironically, I have in my published work and debates offered a more robust natural theology and presentation of Christian evidences than most self-described evidentialists. I find it odd that because I also believe that there is a self-authenticating witness of the Holy Spirit, that fact is thought to somehow undermine the arguments and evidence I present. I suspect that people are just reacting emotionally to my claims about the witness of the Spirit rather than making the effort to engage my arguments in detail premiss by premiss.
I've addressed your final question in Reasonable Faith, 3rd ed., pp. 48-50. Of course, anyone (or, at least any sort of theist) can claim to have a self-authenticating witness of God to the truth of his religion. But the reason you argue with them is because they really don't: either they've just had some emotional experience or else they've misinterpreted their religious experience. So you present arguments and evidence in favor of Christian theism and objections against their worldview in the hope that their false confidence will crack under the weight of the argument and they will come to know the truth. (This also is what the atheist should do with me.) Of course, in presenting such arguments, you are not working against or apart from the Holy Spirit. He is at work, too, testifying to their hearts of the truth of the Gospel and using your arguments, as you lovingly present them, to draw that person to saving faith in Christ.