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Metus comments on Open Thread, April 27-May 4, 2014 - Less Wrong Discussion
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"The burden of proof is on you."
No, most of the time the burden of proof is on both parties. In complete absence of any evidence both the statement and its logical negation have equal weight. So if one party states "you can't predict the shape of the bottle the liquid was poured out of from the glass it is in" and the other party states the opposite, the burden of proof lies on both parties to state their respective evidence. Of course in the special case above the disagreement was about the exact meaning of "can" or "can't" but the general principle still holds. For any given closed system the number of molecules will be either even or odd. So any arbitrary choice of statement will have to be justified. The burden of proof lies on either party claiming the truth of either position.
A burden of proof depends on the context. If you want to convince me to adopt then you have to fulfill a burden of proof and convince me that's a good decision for me to make. If you want simply want to talk about your experience that your new dog is awesome, you don't have to fulfill any burden of proof to me.
If a company wants to bring a new drug on the market they have to establish it's clinical benefits in two statistical significant clinical trials. On the other hand adverse effects have a lower burden or proof. You need far less evidence for the FDA to get a company to bring up a certain effect as adverse effect for a drug.
Is truth different for benefits then adverse effects? No. But burden of proof is. Burden of proof always depends on the purpose for which you want to use information.
If you ask me: What do you believe about topic X? I don't have any burden of proof to prove that my beliefs on X are true. I only have a burden once I want you to change your belief.
If one party is espousing a hypothesis which has a very low prior probability, then they suffer the burden of providing evidence to support this hypothesis. Finding evidence takes time and resources; if you want to support the low probability hypothesis, then you spend the resources.
But there is never "complete absence of any evidence." For example, if I claim to you that I have an invisible flying pig in my backyard, we both have a lifetime of experiences to draw on which are inconsistent with such a claim. e.g. witnessing pigs and similar animals running around but not flying; feeling solid objects which have always been visible in normal light; and so on. So I would bear the burden of proving my claim.
What is this "burden of proof" and for what purposes is it a useful concept? There are factual questions and people with some capacity and motivation for pursuing them. When social norms dictate how this pursuit should proceed, it's no longer about the questions.
One sense of "burden of proof" seems to be a game-rule for a (non-Bayesian) adversarial debate game. It is intended to exclude arguments from ignorance, which if permitted would stall the game. The players are adversaries, not co-investigators. The player making a novel claim bears the burden of proof — rather than a person criticizing that claim — so that the players actually have to bring points to bear. Consider:
A: God loves frogs. They are, above all other animals, sacred to him.
B: I don't believe it.
A: But you can't prove that frogs aren't sacred!
B: Well of course not, it never occurred to me to consider as a possibility.
At this point the game would be stalled at zero points.
The burden-of-proof rule forbids A's last move. Since A started the game by making a positive claim — the special status of frogs — A has to provide some evidence for this claim. B can then rebut this evidence, and A can present new evidence, and then we have a game going:
A: God loves frogs. They are, above all other animals, sacred to him.
B: I don't believe it.
A: Well, the God Book says that God loves frogs.
B: But the God Book also says that chickens are a kind of flea, and modern taxonomy shows that's wrong. So the God Book isn't good evidence.
A: I found a frog once that had the word "God" encoded in the spots on its back in Morse code.
B: But the spots on frogs' backs are probably pretty random. How many frogs did you have to check?
A: Umm ... a few thousand. It was a sacred duty!
B: But it would be a lot more convincing if all frogs had that pattern, wouldn't it?
A: Well ... Frogs are sacred in Homestuck, which is the most financially successful webcomic of all time. Surely that's a sign of God's favor.
B: They're sacred to Prospitians, yes, but Dersites think they're blasphemous. Besides, if financial success was a sign of God's favor, we should all be worshiping Berkshire Hathaway, not frogs.
According to the rules of the game, B doesn't have to establish that God hates frogs. B just has to knock down each one of A's arguments. Then, since A has failed to establish any evidence that holds up, B is (so far) winning the game.
I like this framing, but "burden of proof" is also used in other contexts than arguments from ignorance. For example, two philosophers with opposing views on consciousness might plausibly get stuck in the following dialog:
A: If consciousness is reducible, then the Chinese room thinks, Mary can know red, zombies are impossible, etc.; all these things are so wildly counterintuitive that the position that the burden of proof falls on those who claim that consciousness is reducible.
B: Consciousness being irreducible would go so completely against all the scientific knowledge we have gained about the universe that the burden of proof falls on those who assert that.
Here "who has the burden of proof?" seems to be functioning as a non-Bayesian approximation for "whose position has the lowest prior probability?" The one with the lowest prior probability is the one that should give more evidence (have a higher P(E|H)/P(E)) if they want their hypothesis to prevail; in absence of new evidence, the one with the highest prior wins by default. The problem is that if the arguers have genuinely different priors this leads to stalemate, as in the example.
ETA: tl.dr, what Stabilizer said.
I'm not sure how Mary knowing red follows from reducible consciousness. Knowing everything (except the experience) of red does not the experience of red make.
It is certainly debatable, but there are philosophers who make this argument, and I only used it as an example.
"Burden of proof" is also formally assigned under judicial frameworks. "Presumed innocent until proven guilty" and "beyond reasonable doubt" are examples of such assignations.
Outside of a legal context, I tend to assume that if someone in a discussion has made an appeal to "burden of proof", that discussion is probably not a fruitful one.
If someone is (or seems like they might be) privileging the hypothesis, it seems reasonable to say that the burden of proof is on them, not just as a social norm but also as a question of epistemology.
In other words, if there are a hundred boxes where the diamond could be and I claim that it's in box number 27, then it's reasonable that I ought to provide some evidence for this claim, rather than requiring the other person to come up with a hypothesis for why my claim would be false. There are an infinite number of false hypotheses, and if we try to test them all rather than focusing on the most promising ones, we'll never get anywhere.