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AIBU?

Share your dilemmas and get honest opinions from other Mumsnetters.

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Original poster

AIBU to not understand how the exception proves the rule?

32 replies

J2Od · 11/03/2026 08:00

Please help me understand how the exception is supposed to prove the rule.

OP posts:

Gwenhwyfar · 15/03/2026 11:51

AlexRidersButt · 15/03/2026 11:38

"The proof of the pudding is in the eating" is another phrase where proof mean test, not evidence.

It's like "desert island" - it means deserted, no one living there, not a sandy, arid island.

Or "get their just deserts" which uses desert (pronounced dessert) to mean "that which you deserve".

Lots of sayings use earlier meanings for words.

Show quote history

Yes, but in this case we use the whole expression differently now. We mean that that there IS a rule, not that it is tested.

sophiasnail · 15/03/2026 11:59

There are two ways of thinking about it. A sign in a pub which says "dogs allowed in the bar" proves the rule that dogs aren't allowed in the rest of the pub.

Or, If imagine I always take route A to work because the traffic is worse on route B. One day I take route B and the traffic is terrible. This exception to my usual route has proved my "rule" of always going route A is correct.

DeftGoldHedgehog · 15/03/2026 12:01

WhatAMarvelousTune · 11/03/2026 08:17

@Agixparking example, and @InfoSecInTheCityare right.
But people often misuse this saying - I’d say the black swan example is an example of it being misused. The existence of a black swan is not “the exception that proves the rule”. It actually disproves the “rule” that swans are white. Saying “free parking on weekends” does show the existence of the rule that parking is not free during the week, and is therefore the exception that proves the rule.

Yep, I think that's the problem. People often say it when it doesn't make sense.

BillieWiper · 15/03/2026 12:14

AlexRidersButt · 15/03/2026 11:38

"The proof of the pudding is in the eating" is another phrase where proof mean test, not evidence.

It's like "desert island" - it means deserted, no one living there, not a sandy, arid island.

Or "get their just deserts" which uses desert (pronounced dessert) to mean "that which you deserve".

Lots of sayings use earlier meanings for words.

Show quote history

I didn't know the desert island one! That is interesting. Thank you!

The one that annoys me is people saying 'the proof is in the pudding'?! Like what do they think that means?

AndresyFiorella · 15/03/2026 13:37

'proofreading' is another example of where we still use prove to mean test.

Aparecium · 15/03/2026 14:23

AndresyFiorella · 15/03/2026 11:41

'Prove' used to mean test. It comes from the Latin probare, which is also the root of the verb 'to probe'. So the original meaning was 'the exception that tests the rule'.
As language changes, archaic uses often remain in phrases and idioms long after they've fallen out of use (like e.g. 'at your beck and call' (what's a beck?). What's interesting about this phrase is that we've bent the meaning of it to fit the language change. It's original meaning was much more straightforward and logical. I find all this stuff fascinating!

Beck = beckon. But ‘beckon and’ is difficult to say clearly, so the second syllable slurred away.

Abitofalark · 15/03/2026 14:34

The way I think of it is demonstrating the rule.

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