An engineer, a physicist, and a mathematician are sitting in a train compartment and travelling through some countryside. Presently they come upon a field, which contains a white sheep.
“Oh look, in this country sheep are white!”, exclaims the engineer. “Oh, how unwarranted!”, exclaims the physicist “in this country, there exists a white sheep, on a specific field.” The mathematician just tut-tuts and curses under his breath. “In this country there exists at least one field, wherein there exists at least one sheep, at least one side of which is white.”
Oh, and another great one I enjoy:
An engineer, a physicist, and a mathematician sign up for a psychology experiment. They are each locked in a room with a tin of baked beans, the idea being that they will have to figure out how to open the tin with no tools in order not to starve.
Sometime later, the experimenters check up on them.
First, they come to the engineer’s cell. There’s a contented engineer sitting in the corner, craters on the wall, and the shrapnel of a totally shredded can strewn around. They ask him what he did. “Oh, I just battered it up against the wall.” Fair enough, they think.
Next, they check in on the physicist. They find him somewhat dishevelled, the walls covered with scratched calculations, and a neatly severed can in the middle of the room. They ask him for his account. “Oh, I calculated that if I emitted a note on a certain pitch, resonance would eventually cleave the can in half. It took me some time to figure out the note, though.” Again, fair enough.
Finally they get to the mathematician, whom they find shrivelled up, sitting cross-legged on the floor in front of an intact can as if venerating it, muttering “assume the can is open, assume the can is open”.
:)