Wait, Google says nobody's posted this joke on LessWrong before?

...

A philosopher, a scientist, and a mathematician are travelling through Scotland, gazing out the window of the train, when they see a sheep.

"Ah," says the philosopher, "I see that Scottish sheep are black."

"Well," says the scientist, "at least we see that some Scottish sheep are black."

"No," says the mathematician, "we merely know that there exists at least one sheep in Scotland which is black on at least one side."