In an otherwise good article, American Greatness‘s Edward Ring states:
But the exception proves the rule.
It is a statement that makes no logical sense. Any exception to a rule actually disproves the rule, as a moment’s thought will show, because a rule is that which applies to all relevant circumstances. If there are any exceptions, it’s not a rule but a guideline. (/Captain Barbosa)
So where did this contradictory statement come from? Originally, the verb to prove came from the Latin word probere, which means to test. And yes, that was the word’s original meaning, for example when one “proves” (or tests) a mathematical theorem by subjecting its hypothesis (or theory) to a multitude of conditions. If all the conditions generate the same outcome, the hypothesis/theory becomes a theorem (or rule), and its “proof” means “having been tested”.
I’m probably wasting my time on this, because the phrase has become nigh-ubiquitous, and seldom called into question except during angry rants like this one.
For me, though, it’s still a speed bump.