In the art of rationality there is a discipline of closeness-to-the-issue—trying to observe evidence that is as near to the original question as possible, so that it screens off as many other arguments as possible.
The Wright Brothers say, “My plane will fly.” If you look at their authority (bicycle mechanics who happen to be excellent amateur physicists) then you will compare their authority to, say, Lord Kelvin, and you will find that Lord Kelvin is the greater authority.
If you demand to see the Wright Brothers’ calculations, and you can follow them, and you demand to see Lord Kelvin’s calculations (he probably doesn’t have any apart from his own incredulity), then authority becomes much less relevant.
If you actually watch the plane fly, the calculations themselves become moot for many purposes, and Kelvin’s authority not even worth considering.
The more directly your arguments bear on a question, without intermediate inferences—the closer the observed nodes are to the queried node, in the Great Web of Causality—the more powerful the evidence. It’s a theorem of these causal graphs that you can never get more information from distant nodes, than from strictly closer nodes that screen off the distant ones.
Jerry Cleaver said: “What does you in is not failure to apply some high-level, intricate, complicated technique. It’s overlooking the basics. Not keeping your eye on the ball.”1
Just as it is superior to argue physics than credentials, it is also superior to argue physics than rationality. Who was more rational, the Wright Brothers or Lord Kelvin? If we can check their calculations, we don’t have to care! The virtue of a rationalist cannot directly cause a plane to fly.
If you forget this principle, learning about more biases will hurt you, because it will distract you from more direct arguments. It’s all too easy to argue that someone is exhibiting Bias #182 in your repertoire of fully generic accusations, but you can’t settle a factual issue without closer evidence. If there are biased reasons to say the Sun is shining, that doesn’t make it dark out.
Just as you can’t always experiment today, you can’t always check the calculations today.2 Sometimes you don’t know enough background material, sometimes there’s private information, sometimes there just isn’t time. There’s a sadly large number of times when it’s worthwhile to judge the speaker’s rationality. You should always do it with a hollow feeling in your heart, though, a sense that something’s missing.
Whenever you can, dance as near to the original question as possible—press yourself up against it—get close enough to hug the query!
1Jerry Cleaver, Immediate Fiction: A Complete Writing Course (Macmillan, 2004).
2See also “Is Molecular Nanotechnology ’Scientific’?” http://lesswrong.com/lw/io/is_molecular_nanotechnology_scientific.