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, there is no language wherein a double positive can form a negative."

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

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A SHORT HISTORY OF MEDICINE:

I have an earache...

2000 B.C. - Here, eat this root.
1000 A.D. - That root is heathen. Here, say this prayer.
1850 A.D. - That prayer is superstition. Here, drink this potion.
1940 A.D. - That potion is snake oil. Here, swallow this pill.
1985 A.D. - That pill is ineffective. Here, take this antibiotic.
2000 A.D. - That antibiotic is artificial. Here, eat this root.