Very true.
A Mathematician, a Physicist, and an astronomer were traveling north by train. They had just crossed the border into Scotland, when the Astronomer looked out of the window and saw a single black sheep in the middle of a field. "All Scottish sheep are black," he remarked."No, my friend," replied the Physicist, "Some Scottish sheep are black."
At which point the Mathematician looked up from his paper and glanced out the window. After a few second's thought he said blandly: "In Scotland, there exists at least one field, in which there exists at least one sheep, at least one side of which is black."