Q: A waitress walks up to a breakfast table with five logicians and asks, 'Does everyone here want coffee?'No doubt the waitress has to be a logician too. This reminds me of a related joke:
The first logician says, 'I don't know.'
The second logician says, 'I don't know.'
The third logician says, 'I don't know.'
The fourth logician says, 'I don't know.'
And the fifth logician says, 'No.'
To whom did the waitress bring coffee — and why?
René Descartes walks into a diner and orders a cup of coffee. The waitress asks if he wants cream and sugar to which he replies, "I think not". He promptly disappears.
Edit: The answer isn't too difficult if you just think of each person's reply choices...
A: The waitress asks, "Does EVERYONE here want coffee?"
If the first logician didn't want coffee, he knows that not EVERYONE wants coffee so he could have replied "No." But he doesn't yet know what the others are thinking so he answers "I don't know." This tells us he wants coffee.
Similarly, the second logician has determined that the first logician wants coffee. Now we are in the same situation as the first logician. If the 2nd logician didn't want coffee, he could say, "No." But because he replies "I don't know." it means he also wants coffee.
The same logic applies to the 3rd and 4th logicians.
The fifth logican has determined that all the rest want coffee. If he also wanted coffee, he would reply "Yes" because he can accurately determine that everyone wants coffee. However, he doesnt want coffee and therefore answers "No", because he is the lone logician that doesn't want coffee and therefore NOT everyone wants coffee.
The waitress (being the consumate logician herself) brings coffee to logicians 1 through 4. Logician 5 is not served coffee.