This is a really cheap post.  I labor over some of my posts.  I use punctuation and everything.  For this one, I am going to point you to the website  (The Phrase Finder) that deserves the credit for this and then just say a few things that I feel like saying. 

“The exception proves the rule.”  I have never understood this saying.  Why does an exception prove anything? To the best of my recollection, I have never used it.  Ordinarily, I am the guy who is pointing to the regularities; to the rule.  It is the other guy who is saying that the rule doesn’t apply at the moment.  And since it didn’t really mean anything, it couldn’t be refuted.  It was just an annoyance.

The Phrase Finder cites this situation—my situation—first.  “To the untutored ear it might appear to mean “if there’s a rule and I can find a counter-example to it, then the rule must be true.”  This is clearly nonsense; for example, if our rule were ‘all birds can fly’, the existence of a flightless bird like the penguin hardly proves that rule to be correct.  In fact, it proves just the opposite.”  So here, my opponent would be arguing that that the existence of a flightless bird proves that all birds can fly.  It is, as the Phrase Finder notes, “clearly nonsense.”

I came to this topic yesterday because Dr. Andrew Novella, whose lectures I have been listening to, (see: Can You Be Too Skeptical?) pointed out that “the exception that proves the rule” has been widely misunderstood.  The reason it has, he says, is that we don’t understand that “prove,” in that formulation, means “test.”  The exception tests the rule.

Of course it does.  I have had a particular affection for the word anomaly ever since I learned that it is formed of an-, a negative prefix, and homalos, “even.”  An anomaly is an unevenness: a bump in an otherwise flat plane.  It is an anomaly.  It is an exception.  Does this exception “test” the rule?  Do we want to call this plane “flat,” even though there is this exception?

I liked that a lot better.  But if you go to the Phrase Finder hyperlink, you will find this response to that explanation.  “Unfortunately, when we go back to the legal origin of the phrase, we see that it doesn’t mean that at all.” 

The origin is the maxim, “Exceptio probat regulam in sasibus non exceptis” and is interpreted to mean “exception confirms the rule in the cases not excepted.”  The exception points out, in other words, what the rule is: it does this in the process of removing one instance from the rule.  Phrase Finder’s example is: “If we have a statement like ‘entry is free of charge on Sundays,’ we can reasonably assume that as a general rule, entry is charged for.  So, from that statement, here’s our rule—you usually have to pay to get in.”

Think about the realities—the rules—pointed to by such phrases as: except when accompanied by children; or, without proof of membership; or, unless you are a Democrat.  Every one of those points to a situation that is to be taken for granted—it is a rule—and makes a small exception to that rule.  It is the exception that testifies to the existence of the rule.

Isn’t that satisfying?  Unless, of course, you are a casuist and therefore an exception.