"The exception that proves the rule"

What kind of sense does "the exception that proves the rule" make?

Patty

In terms of usage, you will often hear scientists use this phrase as a short-hand for the value of anomolies (exceptions) in overturning old paradigms (rules) and establishing new ones.

Obviously this is not the origin of the phrase (the earlier poster is right about the origin, I think) but it is one usuage of it that may help you see what kind of sense it makes.

Let's be clear about this: an exception may indeed "prove" (that is, test) a rule... but it doesn't automatically mean it passes or fails the test. On some occasions, an exception will test, and then overthrow, the rule. On other occasions, an exception will test a rule, and still be regarded as an exception: the rule will, by and large, survive intact.