zlacker

I thought it was more along the lines of prove = test; the exceptions clarify the rule. Or in AI training terms, you need negative test cases as well as positive test cases to adequately define a rule.

Thou shalt not kill, except all the times thou shalt.

>>saalwe+(OP)
Words being what they are, and us not speaking the language that created this saying, I'm guessing both general ideas can be true. :D

My memory is this came from Cicero and was about a place excluding women by rule, as they pointed to the exception of a woman that was allowed.

https://en.wikipedia.org/wiki/Exception_that_proves_the_rule seems to support both interpretations, and at least shows I got the speaker right. Not seeing that my specifics are good, though. I would not be shocked to know that I am wrong there.