Proof of Ignorance

So . . . one of my least favorite expressions in the common vernacular is "the exception that proves the rule." First of all, the expression is almost always used to mean the opposite of what is intended (more on that later), but mostly because it just doesn't make any damn sense.

If there is an exception to a rule, it is not a rule! Seems simple enough. Using a (now overused, thanks to brilliant author Nassim Nicholas Taleb) example, if the rule is "all swans are white," then an exception (a black swan) does not prove the rule, it disproves it. Not to get all Popperian (that's Sir Karl Raimund Popper the philosopher and professor, not John Popper the musician and gastric bypass patient, or Popcorn Popper, the provider of delicious snacks), but once an exception to a rule has been found, it is no longer a rule. Rules do not need an instance of disconfirmation to make them valid.

People tend to (mis-)use this expression when disconfirmatory evidence is found, rather than take the evidence as disconfirmation of the original thought. For example, if someone believes that all Michael Bay movies are good, and then sees Transformers, they may say that this is the exception that proves the rule (I know, I could have substituted any Michael Bay movie title there), rather than taking it is evidence that a) not all Michael Bay movies are good and b) they have horrible taste in movies.

Most maddening is that most people don't even know what this expression means. The word "prove" in the expression does not mean "confirm" or "support," but rather "test." In other words, it is the exception that tests the rule. This makes oh-so-much more sense, as an exception to a rule will test its validity. An exception may also provide evidence of a related rule, such as in this example: A sign says that Shrek 3 is sold out, so by extension, the other films at the cinema are not sold out ("Gee, I wonder if there is a Michael Bay movie I can see instead?"). So if you go to the movies expecting no movies to be sold out, and an exception is found, you at once disprove your original rule and replace it with another.

The word prove has the same meaning in another misunderstood expression, "the proof is in the pudding." The correct expression is "the proof of the pudding is in the tasting." In other words, we test or evaluate the pudding by tasting it. Keep in mind that this is an English (U.K.) expression, so they aren't actually talking about delectable chocolate or butterscotch pudding, but rather something like spotted dick (made of made of raisins and raw fat from beef or mutton - but don't worry, it's served with custard) or black pudding (made of blood and oatmeal). If this sounds appetizing, perhaps you can be the exception that proves the pudding.

Happy proving!