The Burden of Proof
In the recent thread on Huntsman , BlaiseP, Tom van Dyke and I ended up in a bit of a digression of atheism and the burden of proof which I thought was worth teasing out, but not on that thread. The part of the exchange I want to focus on was between Tom and I and went like this:
the atheists need better arguments. They don’t actually have an argument.
Epistemologically we don’t need one. Burden of proof is on the claimant. Occam’s Razor does the rest.
I don’t follow you, but burden of proof is shared in any joint inquiry among persons of good will and lovers of wisdom and truth.
Now I’m not entirely sure what Tom means by sharing the burden, but I assume it means something like neither party has the burden of proof, but that each interlocutor should advance their case as best they can, rather than insisting that the other side should do all the work (tom, feel free to correct me if you meant something else).
This sounds like an eminently fair approach, and is the norm in a debate. But debates are really more oratorical contests than exercises in truth discovery. In science, the best truth discovery mechanism humanity has yet produced, the rule is different – if you wish to allege something exists it is up to you to prove it. The doubters get all the advantage, they need not even get out of their chairs until you’ve done all the work to prove your case, only then must your opponent lift a finger. This may sound like an unfair distribution of responsibility, but in practice there are several good reasons, logical and mathematical, why this should be the case.
Proving a Negative
It is commonly said that you can’t prove a negative, and while this isn’t quite true in all cases it is certainly true that actually disproving the existence of something is a lot harder than proving it. For instance, if tomorrow morning a massive glowing figure descended from the sky proclaiming in a voice heard round the world that it was God Almighty and then proved it had knowledge and powers beyond mortal ken that would conclusively prove it was God, (ruling out advanced aliens or similar deception would take some work) but it would certainly get my attention. By contrast, the failure of any being to do this in recorded history does not rule out the existence of a god or gods. Maybe they’re just not into tacky displays of power.
And that’s the problem in a nutshell. To actually disprove any god in the logical sense I would have to find something incompatible with the existence of that god. This is really hard to do when you’re talking about the Abrahamic God since he’s meant to be omnipotent. If there’s nothing he can’t do then there is no state of the universe that’s incompatible with his existence. As such there is no possible disproof of God’s existence, and expecting an atheist to come up with one is a bit much to ask for.
Even so, you might just conclude that God’s existence is too well-established to be doubted then. But this would be a mistake, as I will explain below.
The Law of Non-Contradiction
You see, the argument used above to prove God’s existence will work for the vast majority of gods. While some gods (like a sun god who rides across the sky in a flaming chariot) are disprovable, even most non-omnipotent deities are sufficiently poorly specified so as to avoid empirical falsification. I mean, how could you tell for certain that the Hindu gods didn’t exist? What about Ba’al or Ahura Mazda?
This may seem trivial, but it is anything but. There are thousands or religions in human history, and they can’t all be right, in fact they are almost all contrary – there is at most one true religion. To prove yours is right you have to demonstrate everyone else’s is wrong. And as I said, you can’t do that for a non-trivial set of religions. So you are left with three options:
A: Believe every religion that you cannot actively disprove is true. This violates the law of non-contradiction and is therefore one of the very few ways in the universe to guarantee you are wrong.
B: Believe whichever religion you want and handwave away the rest. In the logic business this is called Special Pleading. Needless to say, this is not an intellectually honest position.
C: Put the burden of proof on the claimant. Not all religions can be true, but all of them can be false. Refusing to believe in any religion without sufficient proof is the only option that is neither incoherent nor intellectually dishonest.
But, you may well say, isn’t atheism a claim of sorts? And it is mutually exclusive with other religions. So why does it get special treatment? For this we need to leave logic behind and visit my home ground: math.
The Law of Conjunction
The Law of Conjunction is one of the foundational rules of probability theory. I’ll skip the whole math lesson, but the short version is that the probability of a bunch of things happening together is less than the probability of any one of those events happening. The classic example is: “There is a woman named Mary. Is it more likely that she is 1: A bank teller or 2: A feminist bank teller?” The correct answer is 1, whatever the chances are of a given woman named Mary is either a feminist, a bank teller or both, it is mathematically impossible to construct a set of probabilities where Mary is more likely to be a feminist and a bank teller than just a bank teller.
The Law of Conjunction ties in well with Occam’s Razor. So long as you’re careful to define complexity correctly (I’ll leave off discussing Komologrov Complexity because that’s a little outside my area of expertise) the simplest explanation for a phenomenon will be the most probable. So if you want me to add a god to my model of the world, you are going to have to make up for the reduction in probability by adding explanatory power – in other words you need to show me that there are things in the world that make more sense if a god exists than not (this is another way of saying I want evidence). And since any god is a very complex phenomenon you’re going to need a lot of evidence to convince me.
But this is all a matter of probabilities, am I not admitting a chance that a god exists? Well, yes I am, but that means nothing. It is extremely difficult to be 100% certain of anything, and I would suggest most kinds of knowledge can’t be known with 100% certainty. If you’re willing to accept that it is OK to believe unlikely things in favour of more likely alternatives, you end up accepting things like it is perfectly valid to believe that exposing yourself to the Cherenkov radiation of a nuclear reactor will give you superpowers because, hey there’s a chance right? It’s not like any nuclear physicist can say there’s a 100% chance it won’t. Refusing to heed probabilities dissolves all knowledge into a postmodern fog where all ideas are equally valid, and we don’t want to go there, now do we?
I guess this is just a long-winded way of saying that if you want me to believe in your god or gods, I’m going to need you to show me evidence, and until someone does I don’t feel it at all unreasonable to assert that there is almost certainly no God, nor any other gods either.