Three logicians walk into a bar. The bartender asks them, 'Do you all want a drink?' The first logician says, 'I don't know.' The second logician says, 'I don't know.' The third logician says, 'Yes!' What does this mean?
All three logicians want a drink.
The bartender asked if *all* of them wanted a drink. If even one of them did not want a drink, that person would have immediately answered 'No' (since 'all want a drink' would be false). The first logician wanted a drink himself, but didn't know if the other two did, so he said 'I don't know'. The second logician also wanted a drink, heard the first's uncertainty, and realized he didn't know either. The third logician, knowing that both of his friends wanted a drink (otherwise one would have said no) and wanting one himself, triumphantly answered 'Yes!'.
About this riddle
Logic riddles give you a few facts and ask what must be true. List what you know, cross out what cannot be, and see what is left.
Difficulty: Medium. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
More logic riddles
If two's company and three's a crowd, what are four and five?
A queen, a king, and a jack are placed in a row face down. The jack is to the right of the queen. The king is not on the far right. Which card is in the middle position?
What English word becomes shorter when you add two letters to it?
I am white and floaty, and I can pass through walls. What am I?
Three boxes are labeled 'Apples', 'Oranges', and 'Mixed'. You know that EVERY box is incorrectly labeled. You pick one fruit from the box labeled 'Mixed' without looking inside, and it is an Apple. What are the correct contents of all three boxes?
Five books are stacked on a shelf from top to bottom: Chemistry, Physics, Biology, History, and Art. You pick up the Chemistry book, place it at the very bottom of the stack, and then take the top book of the new stack and place it directly beneath the Biology book. What book is now in the exact middle (third from the top) of the stack?