[sunstone]

The version I know goes like this:

A physicist, a mathematician and a logician are taking the train to Scotland. As the train crosses the border they see a black sheep on a hillside. The physicist remarks, "Oh look all the sheep in Scotland are black." The mathematician replies, "Oh you can't quite conclude that, the most you can say is at least one sheep in Scotland is black." Then the logician says, "Well really the most you can say is that at least one sheep in Scotland is black on one side."