As a statement about proof, the phrase 'the exception proves the rule' is nonsense. Proof comes from the affirmation of a meaningful proposition, and behavior that contradicts a rule can scarcely be said to confirm it. But consider instead that the word 'prove' at one time meant 'provide,' and then make the substitution. Does the exception provide the rule? Indeed it does. It tells us the boundary conditions for the application of the rule: IT' before "e" except after "c"; months have thirty or thirty-one days, excepting February. This is the case even, perhaps especially, in law: all persons born in the United States are eligible to serve as president, except those who would be under the age of thirty-five when inaugurated.
Against this idea of law is the notion that law can never fully provide rules for the uncertainties and crises of life and, therefore, the exceptional is the essentially not-rule-bound. This is the import of Carl Schmitt's famous statement, "Sovereign is he who determines the exception," and this is the charge made against U.S. behavior on the international scene. It is alleged that the U.S. has sought an imperial role in the world, deciding when and when not the rules of law apply to it. As Schmitt suggested, this would make the U.S. a world sovereign, and that is precisely what it is accused of becoming.
International Law | Law
Philip C. Bobbitt,
American Exceptionalism: The Exception Proves the Rule American,
U. St. Thomas L. J.
Available at: https://scholarship.law.columbia.edu/faculty_scholarship/3674