I've always been baffled by the expression "the exception that proves the rule". It never made any sense why an exception could prove a rule. Shouldn't it prove that the rule isn't true?
I once heard an erroneous explanation that it has to do with the older sense of 'prove' as in testing or trying. The exception tests the rule and makes it harder to establish itself. That made a little more sense, but it turns out to be wrong.
The real explanation is much simpler. I was assuming this was supposed to be some absolute rule. The exception that proves the rule does actually confirm the rule, but it confirms it logically rather than empirically. If it's an exception, there's got to be something it's an exception to, i.e. a rule that it goes against. It obviously can't be an exception to an exceptionless or absolute rule. It's got to be an exception to a true generalization. But it can't be an exception without some such rule that it's an exception to. That's how an exception proves a rule.
Now there's still an illegitimate use of this expression, and I see it all the time. Whenever anyone states a rule as an absolute, and someone shows that the rule is false by finding a counterexample, they can't respond by saying that it's the exception that proves the rule. No, it in fact disproves the rule, since the rule was stated as an absolute without exception. So what I was objecting to all along was indeed an illegitimate rhetorical move. It's just that the expression has its origin in a perfectly legitimate point that can be made. It's just not what people usually mean by the expression now.
For more information, see the Wikipedia entry on this. (Yes, unbelievably, it's got its own Wikipedia entry.)
No, it in fact disproves the rule, since the rule was stated as an absolute without exception.
There's the rub. Is it really being stated as an absolute without exception, or is it a generalization that is true in the vast majority of cases? We speak like that all the time: I was recently told when I went to a computer store looking for rewritable DVD-Rs that they didn't carry them because "no one buys them." Well, clearly that's not true in a strictly literal sense: I was there, and I was a potential customer who does buy DVD-RWs, and would have done so at that time if they had had any. "No one buys them" really means, "There isn't a big enough market to justify shelf space for them." It's a rule of thumb rather than a law.
Suppose that for some bizarre reason I became famous in my quest to find off-the-shelf DVD-RWs. At some point, the store clerk might tell someone, "No one buys those," to which that customer will reply, "Well, Scott does." I have become the exception that proves the rule: the fact that I am the one counterexample that anyone can think of, proves how overwhelmingly true (in a general sense) that rule actually is.
That's right. People often speak in true generalizations. But I've seen people use "that's the exception that proves the rule" in a context where it had been clear that the rule was supposed to be exceptionless.
I thought that the best interpretation was that exceptions to rules helped prove the rule that every rule has an exception (except this one). Still not a very good rule, since there are some rules (or generalizations) which have no exceptions.
Jeremy, thanks for interesting points.
Students of English encounter these "exceptions" that are a goood example of the fact that in specific sentences one grammar rule is "overpowered or overruled" by another.
I just wanted to mention a motto from a textbook on probability: If every rule has an exception then combinatorial rules are an exception because they have no exception (I think that in the sentence you can say "absolute" instead of "combinatorial"). This is an interesting sentence that combines the loose approach and the thoughtful one.
"OK, go to the party, but the rule is you've got to be back by midnight."
"But that's not fair. Last week you let me stay out till dawn!"
"That's because it was your birthday. That was an exception. The exception proves the rule."
I.e. The fact that last week was exceptional shows that some other norm or rule applies to most weeks.
It's a way to cope with extraordinary cases without setting a precedent.
Yes, that's how the expression apparently used to work, even if it sounds completely foreign today. An exchange like that, if it occurred today, would not mean anything like that to most people who heard it, but I think that's got to be something like how it would have gone.