A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

What's the meaning of the expression, "That's the exception that proves the rule?"

October 25, 1991

Dear Cecil:

I've heard the following expression from people all over the country and on television. It makes absolutely no sense:

"That's the exception that proves the rule."

Is this a bastardization of some other phrase? If not, what does it mean?

Cecil replies:

Don't you get it? The whole point of this saying is that it doesn't make sense. It's what you say to confound your enemies when your argument has been shot out from under you by some pesky counterexample. From the point of view of advancing the debate it's about one jump ahead of "yo mama," but it beats standing there with your mouth open.

To be sure, a few scholarly types have tried to make excuses for "The exception proves the rule," as the quotation books usually phrase it. They say it comes from the medieval Latin aphorism Exceptio probat regulam. Probat means "prove" in the sense of "test," as in "proving ground" or "the proof is in the pudding." So "the exception proves the rule" means a close look at exceptions helps us determine a rule's validity.

If Latinists understand it that way, however, they're pretty much alone. I've looked up citations of this saying dating back to 1664, and in every case it was used in the brain-dead manner we're accustomed to today — that is, to suggest that non-conforming cases, by the mere fact of their existence, somehow confirm or support a generalization. Obviously they do nothing of the kind. We like to think proverbs become proverbial because they're true; this one is an exception. It certainly doesn't prove the rule.

Exceptional stupidity

Dear Cecil:

I was surprised to see the question in your column about the exception proving the rule because I had always assumed the saying came from the "rule" that "there's an exception to every rule." Thus the mere existence of an exception to a rule proves the validity of the rule. No?

Cecil replies:

No. If all it takes for a rule to be valid is that it have an exception, every rule would be valid — except, of course, rules without exceptions. Obviously not an argument you want to take very far.

Exceptional stupidity, part two

Dear Cecil:

Your reply to the question, "What does `that's the exception that proves the rule' mean?" was not quite right. The quote refers to a logician's axiom: that which can never be false can likewise never be true. If a statement cannot be admitted ever to be false, then it is a concealed tautology, i.e., a dogma. An instance of a proposition's not-being-the-case serves to affirm its existential validity, assuming it does not commit a violation of the rules of logic. Both logical validity AND existential verification are required for one to justly assert that such-and-such is true …

Cecil replies:

You're talking about "falsifiability," Max. If no conceivable evidence could prove a given statement false, then the statement is meaningless. For example, if a psychic comes out with predictions so vague they can't possibly be proven wrong, then the predictions are baloney. Note, however, that contrary evidence merely has to be conceivable. If contrary evidence actually exists, the statement is more than falsifiable, it's false. To put it as clearly as I can, THE EXISTENCE OF AN EXCEPTION DOES NOT VALIDATE THE FREAKING RULE! Quite the opposite. But anybody who can sling around phrases like "existential validity" deserves credit for trying.

Part three and counting

Dear Cecil:

OK, OK, I acknowledge your general brilliance, but I can't stand it another minute. The appropriate provenance of the saying "It's the exception that proves the rule" is psychology, not logic. You can have a rule without an exception, but you can't have an exception without a rule. Therefore, if something appears to be an exception, that indicates that a rule must exist. If you reflexively think of something as an exception, then you can infer that you've already, perhaps unconsciously, postulated a rule. Perceptually, the exception throws the rule into relief. It's analogous to, "It's turning on the light that proves you were in the dark." Read it as "It's the [recognition of an] exception that proves the [existence of a] rule." Geez, it's just a saying, and not a bad one at that.

Cecil replies:

What is this, proverb as Rorschach test? Everybody I've heard from has a different take on this. There is nothing in the literature or common experience to support your farfetched interpretation.

The last word on exceptions

Dear Cecil:

I hate to have to correct Cecil Adams, but the business about "the exception proves the rule" in the latest Straight Dope seems way wide of the mark. The proverb's meaning must be expounded not in the context of natural or psychological law but of civil law. Alan Bliss, in A Dictionary of Words and Phrases in Current English, has the following to say about the origin of this phrase: "Exception probat regulam [Lat.], the exception proves the rule. A legal maxim of which the complete text is: exceptio probat [or (con)firmat] regulam in casibus non exceptis — `the fact that certain exceptions are made (in a legal document) confirms that the rule is valid in all other cases.'"

The application is this. Suppose a law is stated in such a way as to include an exception, e.g., "Parking is prohibited on this street from 7 AM to 7 PM, Sundays and holidays excepted." The explicit mention of the exception means that NO other exceptions are to be inferred. Thus we should take the Latin verb probare in the maxim to have the sense of "to increase the force of."

Cecil replies:

Hmm. It grieves me to say this, but you're right. While the interpretation I gave, namely that the exception tests the rule, has a long history (it dates back at least to 1893), I'll concede that your take on it is the original sense of the proverb.

That said, your example could use a little work. We need something that better conveys the import of this ancient maxim. I have just the thing — an illustration from the Roman orator Cicero, sometimes cited as the source of the legal doctrine in question.

Cicero was defending one Bilbo. (No relation to Frodo.) Bilbo was a non-Roman who was accused of having been illegally granted Roman citizenship. The prosecutor argued that treaties with some non-Roman peoples explicitly prohibited them from becoming Roman citizens. The treaty with Bilbo's homeboys had no such clause, but the prosecutor suggested one should be inferred.

Nonsense, said Cicero. "Quod si exceptio facit ne liceat, ubi non sit exceptum …" Oops, I keep forgetting how rusty folks are on subjunctives. Cicero said, if you prohibit something in certain cases, you imply that the rest of the time it's permitted. To put it another way, the explicit statement of an exception proves that a rule to the contrary prevails otherwise.

You can see where an argument like this would come in handy in traffic court. What's more, it's basically what Kyle Gann was arguing in his letter, although his "psychological" angle obscured matters a bit. Accordingly I withdraw my more abrupt comments.

Still, whatever the original significance of the proverb, we should recognize that its many latter-day interpretations have taken on a life of their own. Since there is not much chance of stamping these out en masse, we may as well resign ourselves to trying to boost the sensible interpretations and suppress the rest. Here it seems to me that the interpretation I initially favored, that the exception tests the rule, comes off pretty well.

I am delighted to find ammunition for this view in H.W. Fowler's respected Dictionary of Modern English Usage (1965), which distinguishes five possible senses of "the exception proves the rule." Sense #1 is the legal (i.e., your) interpretation; senses #3, #4, and #5 are popular constructions of the saying, which Fowler regards as more or less slipshod. But he thinks more highly of sense #2, which we may state this way: an apparent exception to a rule may serve on closer examination to strengthen it. By way of example he writes:

"We have concluded by induction that Jones the critic, who never writes a kindly notice, lacks the faculty of appreciation. One day a warm eulogy of an anonymous novel appears over his signature; we see that this exception destroys our induction. Later it comes out that the anonymous novelist is Jones himself; our conviction that he lacks the faculty of appreciation is all the stronger for the apparent exception when once we have found out that, being self-appreciation, it is outside the scope of the rule — which, however, we now modify to exclude it, saying that he lacks the faculty of appreciating others. Or again, it turns out that the writer of the notice is another Jones; then our opinion of Jones the first is only the stronger for having been momentarily shaken. These kinds of exception are of great value in scientific inquiry, but they prove the rule not when they are seen to be exceptions, but when they have been shown to be either outside of or reconcilable with the principle they seem to contradict."

This is not far removed from "the exception tests the rule." Under the somewhat embarrassing circumstances, that's about the best I can expect.

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