15 MARCH 2008, Page 87

Q. Your excellent comments regarding the integrity of London’s black

taxi drivers (8 March) were marred by your misuse of the expression ‘the exception that proves the rule’. The black taxi rapist of recent weeks is the exception that proves the rule. This expression originally meant ‘it tests the rule and finds it wanting’ (‘proves’ being used in the archaic sense of ‘test’ as in proof of the pudding is in the eating).

S.T., Chirton, Wilts A. To counter your pedantry may I refer you to Brewer’s Dictionary of Phrase and Fable which upholds my use of this expression.