The Power of the English Language

I don't know what the orginal source is, I received this by email from a friend. It's worth sharing:

A linguistics professor was lecturing to his class one day. "In English," he said, "a double negative forms a positive. In some languages though, such as Russian, a double negative is still a negative.

However," he pointed out, "there is no language wherein a double positive can form a negative."

A voice from the back of the room piped up, "Yeah. Right."

Books:
Monstrous Regiment - Terry Pratchett