This debate (vimeo / mp3) suffered to some extent from a surfeit of cordiality and a dearth of substantive debate. Robertson referred to the arguments listed at the back of his book, but he never quite got around to really making them. Here they are:
2. Human mind
3. Moral law
Any or all of these might well weigh in favor of a supernatural rather than a natural explanation, but I found it somewhat odd that he barely even alludes to the arguments which might be deployed to get one from, say, the historical Jesus to the veracity of Christian doctrine. They spend more time arguing about the propriety of the Sunday ferries. No, I’m not making this up.
The Q&A period was as lengthy and perhaps more informative than the debate itself, and I’d give the moderator top marks for moving it right along and calling out those who start into a monologue. All the questions save one went to the churchman, and at that point he was pressed to try to make an argument. Here it is - “If you don’t have an absolute morality, you have no morality.” Here is what that argument looks like, formalized:
1. Morality exists
2. If morality exists, it must be an absolute morality
3. If an absolute morality exists, it must exist in a transcendent mind
4. :. A transcendent mind exists in which morality subsists
Aside from the fact that “absolute morality” seems inherently contradictory (right action is always determined relative to the circumstances in which the moral actor finds herself) premises #2 and #3 are far from self-evident and no argument is given to support them.
This debate was really quite personable and enjoyable, but at the end of it all you’d be hard pressed to come up with an argument which was pressed for or against metaphysical naturalism. All told, I’d give it 3½ stars.