Maybe if the exception is proof of an abuse?

It doesn't. Any exception invalidates the rule.

If the rule is "there are always exceptions"? 🤷‍♂️

It’s an ancient Roman legal term “the exception proves the rule” Imagine a rule on a sign at the local pool The sign says “No running” One day a kid is seen running and someone yells, “no running!” and points at the sign. That kid is the exception. The fact that someone has to say “that’s not allowed” shows the rule is real for everyone else. If there were no rule, nobody would say anything.

Not entirely sure myself. But I think it works a bit like. A is the rule B is not A B is plainly a broken case of A All exceptions of A being broken cases of A and not some other category is evidence that A is in fact a rule.

It comes from a legal maxim, written in Latin as exceptio probat regulam in casibus non exceptis. The idea is that stating an exception confirms the rule exists in all the cases not excepted, so a clearer phrasing would be "the exception that proves the existence of the rule.

Teacher here. It is a misreading of one word. "Prove" used to mean "test", not "confirm": same root as probe, a proving ground, proofing armor. So "the exception proves the rule" means the exception TESTS it. A rule put to a hard case comes out stronger if it holds. There is a legal origin too: exceptio probat regulam. The exception marks the case the rule was never meant to cover, which is how you see where the rule actually applies. What it is NOT: an exception as evidence for the rule. Left unexplained, an exception weakens a rule. Named and placed outside its scope, it sharpens it. Direction matters. Tell me the rule you were testing and I will tell you which one you have.

That's the way English teachers explain away all the inconsistencies in spelling and pronunciation.