Zebras and Mules

Zebras and Mules:

How much can you know by deduction from facts you already know? A famous thought experiment ponders the question:

Suppose you are at a zoo in ordinary circumstances standing in front of a cage marked ‘zebra’; the animal in the cage is a zebra, and you believe zeb, the animal in the cage is a zebra, because you have zebra-in-a-cage visual percepts. It occurs to you that zeb entails not-mule, it is not the case that the animal in the cage is a cleverly disguised mule rather than a zebra. You then believe not-mule by deducing it from zeb. What do you know? You know zeb, since, if zeb were false, you would not have zebra-in-a-cage visual percepts; instead, you would have empty-cage percepts, or aardvark-in-a-cage percepts, or the like. Do you know not-mule? If not-mule were false, you would still have zebra-in-a-cage visual percepts (and you would still believe zeb, and you would still believe not-mule by deducing it from zeb). So you do not know not-mule. But notice that we have:

(a) You know zeb

(b) You believe not-mule by recognizing that zeb entails not-mule

(c) You do not know not-mule.

Knowledge by deduction would normally permit you to reason to not-mule; this experiment suggests we may not be able to do that with confidence.

Of course, all this turns on the question of whether you could really cleverly disguise a mule to look like a zebra. Compare and contrast:






More contrasting than comparing, isn't there? From the shape of the ears to the general confirmation, there's no comparison. Of course, you can breed a donkey to a zebra, and then you get something that looks a lot like a cleverly disguised mule:



But it's neither a mule nor a zebra. It's a zonkey.

The real answer to the question, though, is not "Can I really know if I'm looking at a zonkey or a zebra?" Rather, the real question is, "Whose job is it to be able to know how to tell the difference?" The thought experiment errs by assuming that just because person X can't tell the difference, knowledge isn't possible. It is possible, though, for the zoologist; and he's probably the one who put the sign on the cage. So, can person X know that he's looking at a not-mule? Yes, if the zoologist can be trusted.

Bill Whittle wrote about that, once. That's why the climate-change apostasy is so disturbing: it's a direct assault on that web of trust upon which civilization is founded.