Friday, November 20, 2009

It's Rational to Be Irrational (Sometimes)

A little thought experiment that will help lay the groundwork for later posts:

A rational being is one which always acts to maximize the likelihood of producing optimal outcomes. In other words: A rational being has some set of pre-rational preferences, and a body of available information. Using this information, the rational being evaluates the available courses of action and chooses the one that appears likeliest to produce the most-preferred (optimal) outcome.

We thus already see that a rational being cannot exist without something irrational, namely preferences. But there's a deeper way in which irrationality can be rational.

Imagine that you are in the jungle. You, like all human beings, have a capacity called agency attribution. This is, effectively, an alarm system that notifies you when a sensory input is caused by an intentional act. In other words, it's what distinguishes between leaves rustled by the wind (non-intentional), and leaves rustled by a hungry tiger stalking you (intentional). If you were perfectly rational, you would assign agency wherever there was evidence of an intentional being, and no other time.

However, here in the jungle, tigers are pretty good at hiding. There's a good likelihood that those rustling leaves are a tiger, even though there's no evidence that it's anything other than the wind. If you fearfully and irrationally shoot at every rustling leaf, on the knee-jerk assumption that it's a tiger, you are likelier to survive than if you're purely rational about it.

Increasing your survival chances is, generally, a pretty rational thing to do. So, in this circumstance, behaving irrationally on one level is actually rational on a higher level (meta-rational?) Indeed, I'd speculate that something like this scenario creates a selection pressure for a hair-trigger agency attribution, which would explain why it's a nigh-universal human trait.

Anyway, if this scenario seems oddly familiar, it should be: it's Pascal's Wager, only with a tiger instead of a vengeful God. I'm not arguing that Pascal's Wager should be regarded as a valid argument for belief in God (the difference is that tigers can be demonstrated to exist); only that the kind of irrationality which leads to Pascal's Wager serves a useful function.

Edit for Clarity: What I am arguing, in essence, is that there are circumstances under which a hypothetical, fully rational being, who prefers survival to death, will wish to be less rational. To put this yet another way: there exist selection pressures favoring certain forms of irrationality.


  1. Y'know, I actually had this argument with my brother, who felt absolutely certain that it's possible for a human being to be entirely rational. Some of that was a semantic disagreement, and it got a bit further when I used "pre-rational" instead of "irrational", but I'm still not sure whether I convinced him.

  2. It's not only impossible but inadvisable to be purely rational. Try looking up "bounded rationality", I think you'll find some interesting stuff. Gerd Gigerenzer in particular has some interesting work on how following simple heuristics (such as emotional biases) can, under the right circumstances, produce *better* results than evaluating choices rationally. Most often, this occurs when the cost of evaluating each choice is high -- which is, more or less, what's going on in my tiger example.

  3. [[If you fearfully and irrationally shoot at every rustling leaf, on the knee-jerk assumption that it's a tiger, you are likelier to survive than if you're purely rational about it.]]

    Not if you have limited ammunition. If you have a gun with 20 bullets, the 21st rustle will be the tiger that kills you.

  4. @Jeff: Sorry for the late respone. You sort of have a point, but on the other hand, if tigers are sufficiently common and sneaky (which we are presuming, for purposes of this thought experiment, that they are), *not* firing fearfully at every bush means the third or fourth rustle is the tiger that kills you.


Note: Only a member of this blog may post a comment.