Turek claims that the laws of logic are immaterial and therefore “would not exist if the purely material world of atheism were correct.” Thus, if there are logical laws, there must be a God.
This is a favorite tactic of presuppositionalists. The point is to immediately put a stop to any atheistic argument. If logic depends on God, then any reasoning the atheist uses presupposes that God exists and is therefore self-defeating.
Judging by YouTube, the tactic works on many. It isn’t easy to explain the existence of logic itself, after all, and presuppositionalists use this to their advantage. It’s an easy way to trip-up their opponents.
But of course the idea that it is logically possible for logical laws to not apply is incoherent. What would a world without logical laws be like? Does Turek think that if there were no God, a cat could fail to be a cat, or that two plus two might sometimes equal seven? Just as our physical laws apply to the actual world, logical laws apply to any world there could be. They describe what must be the case no matter what. It makes no sense, therefore, to claim that they are dependent on anything, including God.
The claim that they do depend on God can be understood in two ways. It can either mean that God decides what logical laws will be true, or it can mean that logical laws are part of God’s nature. The first option really makes no sense. Not only is it impossible for principles like the law of identity to fail to apply — God could not exist, or do anything, unless logical laws apply. But the second option makes no sense either if it is meant to imply — as the presuppositionalists believe — that the laws are part only of God’s nature, and not of anything else.
The confusion here is due to thinking that, since the laws of logic aren’t physical, they must be mental — and so must be the properties of some mind. (And, the presuppositionalist adds, because our minds change and don’t always agree, unchanging, objective logic cannot be a property of our minds.) But that’s a bit like arguing that, since justice isn’t blue, it must be some other color.
If logic were a mental property, it would not apply to a world without minds. And that’s simply illogical.
PRESUPPOSITIONALISM, PART 2 - LOGIC
ON MATT SLICK'S TRANSCENDENTAL ARGUMENT
[Originally published at Debunking Christianity]