Certain exceptions, it is said, prove the rule.
This has sometimes been understood to mean that identifying a given instance of a phenomenon as exceptional implies the existence of a rule to which it does not conform. The exception may then direct our attention to special circumstances under which the rule does not apply. Alternatively, under an older meaning of the word ‘prove,’ the phrase suggests that exceptional cases test or call into question taken-for-granted rules or expectations.
Given that even analytical or theoretical categories are often freighted with normative or moral significance, the stakes of such questioning may extend well beyond its contributions to scholarly knowledge.