Well, it would give a more solid ground to his argumentation. Neither rationalism nor irrationalism can provide that. He takes things for granted for which his metaphysical and epistemological assumptions cannot account--some would call this "living on borrowed capital." As it stands, he argues very well from the starting point that _humans act_, and deduces from there--but there are important facts to consider that are logically prior to that starting point that should influence his downstream argumentation. You'll likely pick up that I'm referring to the debate between revelation and reason as competing sources of knowledge--when, for my part, I agree with one philosopher who has said "reason is, itself, a revelation."
Discussion
Which philosopher are you referring to?
Cornelius Van Til
Can you suggest some references please?
Especially regarding the origin of reason being revelation
Fair warning: Van Til is heaving sledding, to be sure. He "wrote in English, but he thought in Dutch." You might start with _The Defense of the Faith_ to ease into it, or _A Christian Theory of Knowledge_ if you want to jump in with both feet. I can't say for sure where that exact quote came from, but the thrust of it is scattered through many of his writings. I read a dozen(?) of his books, and they've rather blended together over the years.
yea I've never been convinced that it's justified to bring that stuff into the equation.
For the sake of argument, say that the God of the Christian Scriptures does exist--and has spoken. Shouldn't that influence...everything? I believe he does, and he has--so cannot justify leaving him _out_ of the equation. (In fact, I'd have a hard time justifying _equations_ at all--but that's beside the point.)
This is kind of the argument of _presuppositional apologetics_ -- no one argues from a position of 'neutrality.' We start with God, we end with God -- or we start rejecting him, and end without him too. At the top rung of every logical chain of argumetn is that principal starting point: God is, _therefore_... or God is not, _therefore_... Dostoevsky got at the heart of this when he said, "If there is no God, then all things are permissible."