Originally Posted by joetapley

There's an old story (which if I sort of remember) involves a philosopher, a physicist and a mathematician travelling on a train to Scotland and through the window they see a black cow standing in a field.

The Philosopher says "Look - cows in Scotland are black!".
"No" says the Physicist "Some of the cows in Scotland are black"
"No" says the Mathematician "In Scotland there is one field in which there is a cow which is black on one side"

The moral is that one needs to be careful about what conclusions you reach from observations or experiments.