The phrase "the exception proves the rule" is commonly interpreted as meaning that exceptions support the existence of a rule. However, many find it challenging to articulate how an exception can validate a rule. At first glance, it seems contradictory for an exception to substantiate something it does not conform to.
The key to understanding this phrase lies in the historical meaning of the word "prove," which once meant to test. Thus, when we reframe the statement, we see that the exception actually serves as a test of the rule in question, providing a clearer understanding of its validity.