Many Reasons

by [anonymous] 1 min read25th Jul 20096 comments


I'm here to teach you a new phobia. The phobia concerns phrases such as "for many reasons".

Rational belief updating is a random walk without drift. If you expect your belief to go up (down) in response to evidence, you should instead make it go up (down) right now. If you're not convinced, read about conservation of expected evidence, or the law of iterated expectations.

If evidence comes in similar-sized chunks, the number of chunks in the "for" direction follows a binomial distribution with p=.5. Such a distribution can output most of the pieces being in the same direction, but if the number of pieces is high, this will happen quite rarely.

So if you can find, say, ten reasons to do or believe something and no reasons not to, something is going on.

One possibility is it's a one in a thousand coincidence. But let's not dwell on that.

Another possibility is that the process generating your reasons, while unbiased, is skewed. That is to say, it produces many weak reasons in one direction and a few strong reasons in the other, and it just happened not to produce such a strong reason in your case. And so we have many empirical reasons to think the Sun will rise tomorrow (e.g., it rose on June 3rd 1978 and February 16th 1260), and none that it won't. But this does not seem to describe cases like "what university should I choose", "should I believe in a hard takeoff singularity", or "is global warming harmful on net".

Another possibility (probably a special case of the previous one, but worth stating on its own) is that what you're describing as "many reasons" is really a set of different manifestations of the same underlying reason. Maybe you have a hundred legitimate reasons for not hiring someone, including that he smashes furniture, howls at the moon, and strangles kittens. If so, the reason underlying all these may just be that he's nuts.

Then there's the last, scariest, most important possibility. You may be biased toward finding reasons in one direction, so that you will predictably trend toward your favorite belief. This means you're doing something wrong! Luckily, thinking about why you thought the phrase "for many reasons" caused you to find out.

In sum, when your brain speaks of "many reasons" all going the same way, grab, shake, and strangle it. It may just barf up a better, more compressed way of seeing the world, or confess to confirmation bias. 

(Incidentally, this also applies to the phrase "in many ways". If you judge someone to be in many ways a weird person, that suggests he has some underlying property that causes many kinds of weirdness, or that you have some underlying property that causes you to judge his traits as weird. Both are noteworthy.)