Opiniatrety

Norms of Guessing

via Marginal Revolution, Bryan Caplan writes:

One of the most frustrating things about non-economists is their reluctance to guess. Latest example: Today at the repair shop.

Mechanic: The freon's going to leak out unless we replace the compressor.

Me: How fast?

Mechanic: Don't know.

Me: Could you take a guess?

Mechanic: Nope. Could be tomorrow, could be a year.

You could say that the mechanic doesn't want to convey a false sense of certainty. But surely I let him off the hook when I asked him to guess, didn't I? You'd have to have an awfully short fuse to get mad at someone for being wrong after explicitly asking them to guess.

This strikes me as a straightforward case of the mechanic conforming to norms of assertion, where in this case guessing is a species of assertion. Or if you like, guessing is continuous with assertion and the norms of guessing are continuous with the norms of assertion.

For whatever the mechanic may guess, his guess had better be some sort of guide to the truth. If not, it's a bad guess. Caplan is presumably relying on the mechanic's superior expertise to guide him in some sort of decision; if the mechanic's guess leaves Caplan no better informed than he was before, it won't have been helpful. (And it'll have destroyed what we might call super-Socratic ignorance: Caplan's knowledge that he has no idea.)

We can go even farther. Caplan presumably wants to use the mechanic's guess to make a decision about what to do with the appliance. The mechanic may know that, even if he has some degree of support for a belief about how fast the freon will leak out, that degree of support won't be high enough for any action Caplan might take. So there's good reason for the mechanic to refuse to say anything. Whatever slight degree of support Caplan might get from his guess, he's still better off acting as if his decision were being made under conditions of total ignorance.

Note that the dread knowledge account of assertion plays no role here. The mechanic is explicitly asked to make a guess and permitted to disclaim knowledge. Still, the norm of this guess is that it should be true, or at least likely enough to be true enough for the current purposes. Since it is a guess, those purposes don't require it to be very likely to be true; but it's still possible that any guess won't meet those very low standards.

My own guess is that Caplan wants the mechanic to guess because he thinks preferences should conform to the Savage axioms, so probabilities can be assigned to everything. That's why he complains that it's non-economists who won't guess. On this view there's no difference between risk and ignorance, and you can always adjust your probabilities a micron to reflect whatever new information you have. The mechanic also ought to be able to come up with an expected value for when the freon will leak out. So if you assign probabilities to everything, you should be able to communicate to other your guesses as to what the probabilites should be. But you shouldn't assign probabilities to everything, so sometimes you shouldn't even be prepared to venture a guess.

Posted by Matt Weiner at April 13, 2006 10:13 PM