In any dispute, one side is usually assigned the “burden of proof.” The burden of proof is the obligation to make a convincing case. The burden of proof doesn’t mean you have to prove your position – you just have to show it's more likely than the other position.
When one side has the burden of proof, the other side becomes the “default” position – the one that is accepted if the burden of proof falls short. The default position does not have to present any evidence or logic at all — it can just wait for the other side to make its case.
The position that is less likely has the burden of proof. Also, the side that first makes a claim usually gets the burden of proof. But the latter is not always true. Imagine saying to a contentious friend, “Elephants can’t fly!” and having your friend respond, “Can you prove they can’t fly?”
You go, “Can you prove they can?”
Your friend goes, “You said it first, so you have the burden of proof.”
Well, there you are. If you go by the principle that the first person to make the claim has the burden of proof, you’re stuck with trying to prove that elephants can’t fly. Any idea how you would do that?
On the other hand, if you go by the principle that the person with the least likely assertion has the burden of proof, you’re home free. Let your friend try to coax an elephant into taking off, since his position is much more unlikely than yours.
But sometimes things are not so clear-cut. Take the following situation: You and your friend are having coffee and as she pours cream into her cup, she remarks offhand, “Say, did you realize a cow has to have a calf before she gives milk?”
You think this is the most ridiculous thing you have ever heard and challenge her. It seems to you that what she said was highly improbable and that therefore she has the burden of proof. But then she says, “You know, I grew up on a farm. My father had a herd of prize winning Holsteins that I had to milk every night.”
Whoa! This changes things. Now you’re talking to a person with experience in the topic in question. Since the only experience you’ve had with cows is the Elsie on Borden’s Ice Cream, it suddenly becomes a little more likely that she is right and you are wrong. Given her experience and your lack of it, the burden of proof of proof has shifted to you. You need to come up with evidence that cows can give milk without even thinking of a bull. Good luck!
Finally, let’s consider a controversy of a different kind. Say you have been working out at the gym. Your favorite exercise is running a few miles on the treadmill. You want to be sure that you are getting the same workout as when you run on the college’s track. You believe that because you remain stationary while the treadmill moves beneath you as you run (you have to lift your feet off the track) it must be easier to run on a treadmill. You tell your friend that you are going to run farther to compensate for this. Your friend says not to bother, it’s same effort either way. An argument breaks out. You claim she has the burden of proof because it stands to reason that all you need to do is lift your feet like you’re running and the treadmill will move beneath them. That’s got to be less work! Neutral bystanders give no help at all: Two say you’re right, and two say your friend is right. So who has the burden of proof? From your perspective, there’s no way to say which position is more likely to be correct. The burden of proof at this point is up for grabs. No conclusion can be made until there is further evidence to tip the balance.
This is the most contentious of arguments, when neither side seems more probable. What makes it worse is that there is no easy way to test it. You could of course go on arguing this forever, but there’s a simpler way: Why not ask somebody who knows? You go to your physics professor.
Which is easier, you ask, running on a track or on a treadmill? Without hesitation your physics professor answers, “They’re both the same. It’s just as much work running on a treadmill as it is running on a trackl.” This still doesn’t seem right to you. He tries to explain it but you can’t follow his convoluted explanation.
Now what? Do you go with your gut feeling or what your physics professor says? Physics professors have been wrong before.
That’s true, but who is more likely to be correct, you, who by luck got a C- in introductory physics, or your physics professor who spent 8 years studying and doing research for his doctorate?
Here we invoke the principle of which is most likely. Since it seems more probable that your physics professor would have the right answer, his position becomes the more likely one. So, if you want to pursue this you have the obligation to show you are right. If you can’t, we accept with your friend’s opinion. (At this point you’d be wise to drop the whole thing – because you’re dead wrong!)
There is nothing wrong per se with disagreeing with a professor. Professors are sometimes wrong. But realize that the odds are against you. The professor is much more likely to know things, especially in his/her subject. So if you feel strongly that the professor is mistaken, realize that you have the burden of proof. Also realize that some professors (not saying who) find it annoying when students with very little knowledge stubbornly refuse to consider what the instructor is trying to teach them because that’s not what they’ve always been taught.
1. The person who first makes the statement usually, but not always, has the burden of proof.
2. The burden of proof is determined by which side is least likely.
3. If you have the burden of proof, all that is necessary to satisfy it is to present enough evidence that makes your position more likely than your adversary’s. Remember, you can’t totally “prove” anything!
4. In general, the burden of proof falls on the side that is going against what informed people believe.