Mike - True Blue Tinter
Well-Known Member
Proofs, as in the archaic verb to test
'It's the word exception rather than prove that is causing the confusion here. By exception we usually mean 'something unusual, not following a rule'. What it means here though is 'the act of leaving out or ignoring'. 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.
The exception on Sunday is demonstrating that the rule exists. It isn't testing whether the incorrect rule 'you have to pay' is true or not, and it certainly isn't proving that incorrect rule to be true.
Origin
It's a legal maxim, established in English law in the early 17th century. Written, as law was in those days, in Latin:
Exceptio probat regulam in casibus non exceptis
and is interpreted to mean ‘exception confirms the rule in the cases not excepted’