Logic

How can an exception ever prove a rule?

Comments

A rule cannot be proven by there being an exception (a case that violates this rule). So the point of the saying must be that the rule -- understood loosely as a pattern that holds generally or for the most part -- is proved by the fact that a case violating it is recognized as an exception (as exceptional).

For example, you say that John is lazy. I point out that John climbed Wheeler Peak in 1982. You say that the exception proves the rule -- meaning that the exceptionality of the cited counter-instance (I had to go back 24 years to find a good one) confirms your point that John is generally and for the most part lazy.

I think that the expression 'the exception proves the rule' used the word 'proves' in the now perhaps archaic sense of 'tests', which makes the meaning of the expression less paradoxical.

Here is a third answer focusing on the actual history of the expression: www.worldwidewords.org/qa/qa-exc1.htm

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