Some New Year thoughts on presuppositional logic

"Logic" is part and parcel of the nature of existence. How do I know my reasoning has any validity? Simple: I am aware that logic exists. Therefore I can rely on logic when I use reason as a path to knowledge. How do I know logic exists? The fact that I know anything at all is an indication that the underlying logic of reasoning is valid.

I can assume my reasoning is valid, because if I wasn't able to do it I wouldn't be able to make that assumption. Assuming things is part of the act of reasoning.

Presuppositionalists, however, claim that reasoning is only possible because God exists. They assume that if God hadn't created logic we wouldn't be able to reason, and that because we can reason, therefore God exists.

But logic isn't something separate and above the universe. Logic is not transcendent, it's merely a description of an aspect of the universe as we experience it. Asking whether there are absolute laws of logic is akin to asking if there's an absolute universe. It's like asking if there is matter and energy that is somehow "outside" the matter and energy of the universe, or "beyond" space and time. You might as well ask what happens when an irresistible force hits an immovable object, or what is the mathematical formula for the area of a square circle, or what's the marital status of a married bachelor. These questions don't make sense, and just because they can be asked doesn't mean they have answers. They don't.

Presuppositionalists claim that unbelievers have no basis for assuming that  their reasoning is valid, because (they say) we use unvalidated reasoning in an attempt to validate itself. On the other hand, presuppositionalists assume their reasoning is valid because reasoning was created by God. This, of course, presupposes the existence of God, and is the ultimate God-of-the-gaps argument: the only way that reasoning will work is if it was created by God — therefore God exists. But I would throw the presuppositionalists' question back at them: how do they know that their reasoning is valid? It isn't enough to say that God created reasoning, or even to say that there exist absolute laws of logic that transcend the universe. How do they know that? How do they know that such knowledge is true?

The truth is, they don't.

Presuppositional gymnastics

The following is a reaction to an email exchange between Paul Baird and Sye Ten Bruggencate, posted on the Unbelievable? discussion group prior to today's Unbelievable? programme in which they took part. I've now listened to the show and have only this to add: I came across Sye's website 18 months ago — I thought the argument presented was bogus then, and I think it's bogus now.

The presuppositional argument seems to be predicated at its root on one basic premise — that absolute laws of logic exist. This does indeed sound as if it's true. Without logic we can't know anything is true. Descartes' "I think, therefore I am" would not stand up without logic. But to say that the laws of logic are "absolute" may be misunderstanding the nature of reasoning. To get an inkling of why this might be, consider how the universe would look if there were no such thing as logic. If we couldn't rely on logic to enable us to understand the world, what would the world look like to us? Would it look like anything at all? Isn't even our very existence as conscious entities completely impossible without the existence of logic? In this sense, the existence of logic may in fact be "properly basic" — and consequently we have no need to search for its origin (because, being properly basic, it doesn't have one).

Unfortunately for those unbelievers who engage in discussion with apologists of the presuppositional variety (as well as with those who simply borrow from presuppositional apologetics), any reasoned argument — it can be about anything at all — tends to be met with the rejoinder that the unbeliever surely has no way of knowing how anything is true, because he or she has no absolute logical standard on which to base their "reasoned" arguments. This is extremely tiresome, as it's a debate-stopper. You can't argue with someone who denies that you have any basis for using reasoned argument. Of course, while the unbeliever has no basis for logic, this doesn't however apply to the the apologist, who claims that absolute laws of logic come from God. This claim, like many put forward by apologists, isn't backed up by evidence — it is simply asserted.

Christian apologists in particular may claim that their absolute moral or logical authority is revealed in the Bible, but to do this they have to use the circular argument that the Bible is true because it says it is true (in the Bible). Challenge an apologist on this and they will reply that it's perfectly acceptable to use the Bible as its own authority, because the unbeliever is using logic to verify that logic and reason work, which, the apologists claim, is also circular.

Using logic and reason to verify the truth of logic and reason is not circular, however, if logic and reason are properly basic.

Some apologists of the presuppositional persuasion do seem prone to moralizing from on-high. Maybe this has something to do with their preoccupation with absolutes. In many discussions you are quite likely to see such apologists passing high-handed remarks about the unbeliever's eternal soul, about how the apologist will nonetheless offer up crocodile prayers in the apparently earnest wish that the unbeliever finds God and relents of his or her wicked ways. And if that fails to impress (as it surely does), there will likely be more crocodile regrets that the unbeliever is destined for Hell. All this extraneous nonsense is irrelevant to the debate, and acts as an annoying and alienating smokescreen.

Tiresome is what I called it above, and if I see it in an online discussion or debate it will discourage me from contributing, because I know that the presuppositional mindset is pretty much impregnable — as it is meant to be. Presuppositional apologetics is a field that appears explicitly designed to defend faith from rationality by attempting to undermine the basis for rationality itself.

Here's a (fictitious but typical) example of an effort to undermine rational argument:

Apologist: "Do absolute morals exist?"

Unbeliever: "No."

Apologist: "Are you absolutely sure of that, or is it merely your opinion?"

Disregarding the obvious false dichotomy of that last question, you can see where this is going. If the unbeliever replies that he or she is not absolutely sure that absolute morality doesn't exist, the apologist can continue to claim that it does. If however the unbeliever claims to be absolutely sure that absolute morality does not exist, the apologist will go on to enquire where the unbeliever's absolute knowledge comes from. Swap out morality for logic (or science, or truth), rinse and repeat, and the argument will stall before ever advancing to the field of human instinct, shared values, social cohesion, evolution, kin selection or any other discipline that seeks to explore the modern basis of ethical behaviour.

But the laws of logic are not absolute — in the sense of being separate from the universe. It seems likely to me that "logic" is an emergent property of matter and energy. If the universe didn't exist, neither would the "laws" of logic. That the universe is susceptible to rational analysis doesn't have to be proved; logic isn't contingent, it isn't based on anything.

Logic is properly basic. It just is.