“The exception [that] proves the rule” is a frequently confused English idiom. The original meaning of this idiom is that the presence of an exception applying to a specific case establishes that a general rule existed.
I suspect the main cause of misunderstanding (and subsequent misuse) is omission of the relative pronoun “that”. The phrase should always be “[that is] the exception that proves the rule”, never “the exception proves the rule”.
Your edit updated me in favour of me being confused about this exception-rule business. Can you link me to something?
-Wikipedia (!!!)
(I should just avoid this phrase from now on, if it’s going to cause communication problems.)
I suspect the main cause of misunderstanding (and subsequent misuse) is omission of the relative pronoun “that”. The phrase should always be “[that is] the exception that proves the rule”, never “the exception proves the rule”.
Probably even better to just include “in cases not so excepted” at the end.