Pedantic Language Lesson

I am really tired of people saying that the exception proves the rule, meaning that the exception adds veracity to the original proposition somehow.

"Prove" in this instance means "to test." The exception tests the rule. Proof, like in 86 proof alcohol. Rated at 86 parts alcohol out of 200 (43%), by test. Proofread. Test-read. Proving ground. Testing ground.