The Burden of Proof

Dear people who like debating,
When trying to prove your side, the burden of proof is on you, not on the person you’re debating with. Saying “Here’s my side; prove me wrong” is incorrect. .
Sincerely, anonymous.

I almost lost it when I saw that in my rss feed. (What is “it”?)

See, this is frustratingly close to being right, but ultimately inaccurate. The main flaw is that not every side has a burden of proof; sometimes “prove me wrong” is exactly the right thing to say. In most cases, both sides do have a burden of proof, but not always.

For example, if (just hypothetically) Billy Nye were to debate Ken Ham on evolution versus creationism, both sides make positive claims about the way the universe or at least the world has existed over its history. Specifically, Bill Nye is making the claims that the world is billions of years old and that humans descended from non-humans, just as all other animals descended from not those kinds of animals. Ken Ham, on the other hand, is making the claims that the world is merely thousands of years old and that humans, along with all other kinds of animals, were specially created and have never changed to other kinds of animals. Both sides are making claims, so both sides must present evidence. Is it not enough for Ken Ham to show problems with Bill Nye’s evidence; he must present some evidence of his own, or he has not proved his own claims. This is because evolution versus creationism is not necessarily a dichotomy, as is true of most issues.

Similarly, if two people see an object in the sky, one might claim that the object was an airplane, and the other might claim it was an extraterrestrial spacecraft (I would say UFO, but the object in question is unidentified by definition). The person claiming it was an airplane (let’s call them A) might point out that airplanes are extremely common, and that it left a contrail, as airplanes often do. This would not prove that claim outright, and the other (let’s call them B) might respond by saying that an extraterrestrial spacecraft is likely to create contrails just as well as an airplane. B might further say that the object did not appear to have wings, as most airplanes do. This last point might discredit A’s claim, but does it really prove the object was from another planet? Of course not. The object could well have been a missile, which is much like an airplane without wings, or even a terrestrial spacecraft, or possibly an airplane that was suffering an awful accident wherein it lost its wings. Clearly, in this situation, it would be fairly difficult for either side to actively prove their claim, much more so than the last example due to the lack of available evidence, but I hope the point is clear nonetheless. It would be wrong for B to say “Prove it wasn’t an extraterrestrial spacecraft!” of course, but it would be equally wrong for A to say “No, you prove it wasn’t an airplane!”

However, besides seemingly misunderstanding that both sides of a debate can reasonably have a burden of proof, the above quote also seems unaware of the idea of a null hypothesis.

Let’s revisit the unidentified flying object example. This time, though, A is not making the positive claim that the object was an airplane, but is merely saying that the object was not an extraterrestrial spacecraft. In this case, while B is still making a positive claim that the object was from another planet, A is merely holding the null hypothesis. Therefore, while it would still be irrational for B to say “Prove it wasn’t an extraterrestrial spacecraft!”, it would be perfectly acceptable for A to ask for proof that it was.

Another example is if I make a claim that I have a pet unicorn and someone says “No, you don’t.” It is unreasonable for me to say “Prove I don’t!”, but it is reasonable for them to say “Prove me wrong.” I think most of us understand this intuitively, because if most of us were told someone had a pet unicorn, our first question would be, “Can I see it?” or something similar. In other words, we would ask for proof, and if they said “You can’t prove that I don’t!” we would dismiss them as crazy or say something like “I’ve been to your house and there wasn’t a unicorn there, or really room for one.”

In the same way, a theist makes a positive claim that there is a god, whereas an atheist merely holds to the null hypothesis that there isn’t. Even if the atheist is trying to prove their side, the best they can do is show that the positive god claims they encounter are not properly supported. (Spoilers: I just summarized the majority of all of the content of this blog, because that’s mainly what I do here.) It is exactly right for the atheist to say, “Prove me wrong”. The burden of proof is always on the theist.

I actually went into this in great length in my review of I Don’t Have Enough Faith to Be an Atheist, because the title of the book fundamentally misunderstands this vital point, but the burden of proof and null hypothesis are such important concepts that they deserve a post all their own. They might even deserve a post each, but I can’t talk about one without talking about the other.

On a side note, one of the things I liked about that book is that it accepted the burden of proof, or at least tried to. One of my problems with some Christians I have encountered is that they refuse that burden, instead demanding atheists prove god does not exist. This is simply wrong.

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