The following comes from Elliott Sober (Dept. of Philosophy, University of Wisconsin-Madison, ESober@macc.wisc.edu), who considers it his favorite joke about philosophy:
A boy is about to go on his first date, and is nervous about what to talk about. He asks his father for advice. The father replies: ``My son, there are three subjects that always work. These are food, family, and philosophy.''
The boy picks up his date and they go to a soda fountain. Ice cream sodas in front of them, they stare at each other for a long time, as the boy's nervousness builds. He remembers his father's advice, and chooses the first topic. He asks the girl: ``Do you like potato pancakes?'' She says ``No,'' and the silence returns.
After a few more uncomfortable minutes, the boy thinks of his father's suggestion and turns to the second item on the list. He asks, ``Do you have a brother?'' Again, the girl says ``No'' and there is silence once again.
The boy then plays his last card. He thinks of his father's advice and asks the girl the following question: ``If you had a brother, would he like potato pancakes?''