In no circumstances does an exception prove a rule. None at all. Not one. Never. Ever. Except … … … .* (see footnote)
“Ah, well, you see, that’s the exception that proves the rule.”
I’ve heard these words many times over the years as people try to dodge a contradiction or counter-example. I recall my father serving it up at the dinner table with the roast potatoes. I confess I’ve pulled it out of my pocket on occasion – I didn’t even know it was there! You probably know the phrase too, and because you know it, it has a kind of legitimacy. However, this phrase is – as my father would also say – a nonsense.
Strictly speaking, if they do anything exceptions do exactly the opposite of proving a rule. If your hypothesis fails to account for all relevant phenomena, then that hypothesis is – patently – inadequate. If you encounter an exception, you modify the hypothesis, or you abandon it. That’s the deal.
In the ordinary world, most ‘rules’ are really no more than generalizations posing as something more impressive and though we may urgently wish our deductions could be exerted with the force of truth and knowledge, the truth is they cannot, as a rule.
We have to be flexible, I believe, and humble in the face of counter-evidence. (To those inclined to continue regardless, meet ‘dogma,’ your new friend.)
So, while I wouldn’t go as far as declaring that the exception disproves the rule, I would suggest its existence delimits the rule. An exception reveals a rule’s outline. It removes layers of its clothing, reduces it, strips it of its immediate authority.
The exception disrobes the rule.
And yet, standing there before us, naked and shivering, a rule can still prove to be pretty darned appealing.
* In a legal context it can be argued that the statement of exception indicates the existence of a rule. The textbook example is the street sign which says “PARKING FREE ON SUNDAYS”. This statement would be either incomplete or redundant if parking were permitted on any or all of the other days of the week. From this ‘exception,’ we may infer the ‘rule’ that parking is not free Monday through Saturday.