Three Logicians Walk Into A Bar…

I love the Spiked Math comic strip in general but this one is definitely one of my favorite comic strips of all time. I should use this as a test to determine whether I should circle a stranger in Google+.

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For anyone who doesn’t get it, Paula Rizzuto gave a clear explanation in Google+:

1) Each logician knows that the other two are also logicians and will answer in a particular way.

2) “Everyone” really refers to the 3 customers.

So this is what happens in the cartoon:

1st logician can give a definite answer of “no” if she doesn’t want a beer. But she does want a beer, so she can only answer “I don’t know” to the literal question, because she doesn’t yet have enough information.

2nd logician understands that the first logician could have said no, but didn’t, therefore she wants a beer. But the second logician still doesn’t know what the third logician wants, so can only answer “no” if she doesn’t want a beer or “I don’t know” if she does.

3rd logician understands that both her colleagues must want a beer, because neither said no. The third logician wants a beer, has full information, and can say “yes”.

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