How do exceptions prove the rule?

[coloradodem2005]

Somone was talking about music sucking and saying if the lead singer was replaced, then the music sucks. They referenced Van Halen, "not Van Hagar." Then someone else talked about AC/DC replacing a singer before Back in Black and someone said that is the exception that proves the rule. I just don't quite get the meaning of that.

[kiahzero]

1. It doesn't

It's a stupid saying. An exception breaks the rule.

[AwakeAtLast]

2. Hey, I helped spark a thread!

I usually kill them, I am flattered (I'm the one who made the rule, not the exception).

[Dookus]

3. It has to do with the word "prove"

which in this instance, means to test.

In printing, a "proof" is a test-run. To "proof-read" is to examine something closely.

You test a rule by testing for exceptions to it. The phrase would be clearer by saying "it's the exception that tests the rule".

[coloradodem2005]

4. By this token...

...would that mean that AC/DC sucked on Back in Black and thereafter according to the person who said that this exception proved the rule? I don't quite understand. If the exception tests the rule, and the rule passes the test, then that would mean that the exception is not an exception. :shrug:

[starroute]

5. The best explanation I've seen of this . .

. . . is that seeing mention of an exception tells you there has to be a rule for the exception to be an exception to.

For example, if a college catalog says, "Freshmen with Advanced Placement standing will be allowed to take upper-level courses," you known it means there is normally a rule that Freshmen *aren't* allowed to take those courses.

Of course, I've never been sure if this explanation is the true one or merely the cleverest.