A mathematician, a physicist, and an engineer are riding a train through Scotland.
The engineer looks out the window, sees a black sheep, and exclaims, "Hey! The sheep in Scotland are black!"
The physicist looks out the window and corrects the engineer, "Well, all we know is that some of the sheep are black."
The mathematician looks out the window and corrects the physicist, "Strictly speaking, all we can say is that is that there exists a field in Scotland containing a sheep, at least one side of which is black."
The engineer looks out the window, sees a black sheep, and exclaims, "Hey! The sheep in Scotland are black!"
The physicist looks out the window and corrects the engineer, "Well, all we know is that some of the sheep are black."
The mathematician looks out the window and corrects the physicist, "Strictly speaking, all we can say is that is that there exists a field in Scotland containing a sheep, at least one side of which is black."
- Spoiler:
- Engineers go strictly by what they see and in their case, what they see once is always the same forever. It's standardized.
Physicists assume a little less and are realistic about expectations.
Mathematicians only speak what they can prove, no assumptions. You can only see one side of a sheep at a time without a mirror so you can only prove the visible side is black.