"The Exception that Proves the Rule" Huh, doesn't it do the opposite?

Factual Questions
1

I hear this expression quite often, and, shamefully I can admit to using it myself.

But thinking about it, the expression really doesn’t make all that much sense.

Person A: Every X is Y.

Person B: But what about Z (usually a proven exception to Person A’s statement).

Person A: Well, that’s just the exception that proves the rule.

Person B: Nodding Head Sagely Yes, I guess your right.

But really, that exception doesn’t prove the proposed rule now does it? In fact, it undermines it. Thus this oft used statement really doesn’t make sense. Where did this saying come from, and is there a context where this saying may be true- or at least helpful?

Enlighten me, if you don’t mind.

Thanks!

2

The master speaks: http://www.straightdope.com/classics/a3_201.html

And speaks and speaks and speaks

3

Thank goodness! My first draft included a reference to this being a variation of the famous “Chewbacca Defense” but I thought that might be too snarky for an forum such as this.

Thanks for the link!

:cool:

4

Proves the rule as in tests it.

It would akin to a sign that said, “No Parking Except on Sundays.” Therefore, all other conditions permit parking. It is an argument as a point of law, not of general logic. Cecil answered this one well in the link Qadgop provided.

5

My favorite column ever!