Exception that proves the rule

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"The exception proves the rule" is a saying whose meaning has been interpreted or misinterpreted in various ways. Its true definition, or at least original meaning, is that the presence of an exception applying to a specific case establishes ("proves") that a general rule exists. For example, a sign that says "parking prohibited on Sundays" (the exception) "proves" that parking is allowed on the other six days of the week (the rule). A more explicit phrasing might be "the exception that proves the existence of the rule."

An alternative explanation often encountered is that the word "prove" is used in the archaic sense of "test".[1] Thus, the saying does not mean that an exception demonstrates a rule to be true or to exist, but that it tests the rule. In this sense, it is usually used when an exception to a rule has been identified:[clarification needed] for example, Mutillidae are wasps without wings which cannot fly, and therefore are an exception that proves (tests) the rule that wasps fly. The explanation that "proves" really means "tests" is, however, considered false by some sources.[2][3]

Use in English[edit]

Henry Watson Fowler's Modern English Usage identifies five ways in which the phrase is commonly used, here listed in order from most to least correct.

Original meaning[edit]

The phrase is derived from a legal principle of republican Rome: exceptio probat regulam in casibus non exceptis ("the exception confirms the rule in cases not excepted"), a concept first proposed by Cicero in his defence of Lucius Cornelius Balbus.[4] This means a stated exception implies the existence of a rule to which it is the exception. The second part of Cicero's phrase, "in casibus non exceptis" or "in cases not excepted," is almost always missing from modern uses of the statement that "the exception proves the rule," which may contribute to frequent confusion and misuse of the phrase.

Fowler gives the following example of the original meaning:

Special leave is given for men to be out of barracks tonight till 11.00 p.m.; "The exception proves the rule" means that this special leave implies a rule requiring men, except when an exception is made, to be in earlier. The value of this in interpreting statutes is plain.

This legal principle is classically referred to as inclusio unius est exclusio alterius (Inclusion of one is to exclude the others). The idea is that if the promulgator of law finds reason to enumerate one exception, then it is only reasonable to infer no others were intended. The Ninth Amendment of the United States Constitution was enacted to explicitly suppress this principle by stating that "The enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people."

Scientific sense[edit]

A case may appear at first sight to be an exception to the rule. However, when the situation is examined more closely, it is observed that the rule does not apply to this case, and thus the rule is shown to be valid after all.

Fowler's example is of a critic, Jones, who never writes a favourable review. So it is surprising when he writes a favourable review of a novel by an unknown author. Then it is discovered that the novel is his own, written under a pseudonym. Obviously the rule doesn't apply to this case (although the rule may need to be more precisely stated in future) and the previous evaluation of Jones's ill-nature toward others is re-affirmed.

An example of this use in science writing is laid out by Richard Dawkins in The Ancestor's Tale. Cnidaria is a phylum of animals including jellyfish, corals, and sea anemones. The rule is that all cnidarians, and only cnidarians, have specialized harpoon cells called cnidocytes, which they often use to capture and/or inject venom into prey. There is one exception to this rule. Some species of sea slugs of the nudibranch group have tentacles containing cnidocytes, even though the slugs aren't cnidarians. But it turns out that the slug eats jellyfish and passes the jellyfish's commandeered weapons, intact and still working, into its own tentacles. So examining the only known exception really proved the original rule valid after all.

Loose rhetorical sense[edit]

A rural village is "always" quiet. A local farmer rents his fields to a rock festival, which disturbs the quiet. In this example, saying "the exception proves the rule" is literally incorrect, but it is used to draw attention to the rarity of the exception, and to establish the status of the village prior to the exceptional event.

The general misuse of the phrase is attributable to the ambivalence of the word 'rule'. In the original sense, 'rule' is taken as a strict rule, while in the loose rhetorical sense 'rule' is taken to mean 'rule of thumb'.

A couple of examples of the loose rhetorical use would be to say: because Ted's wearing of jeans to work is considered exceptional, it proves the rule of thumb that most employees do not tend to wear jeans in that setting. The original sense of the phrase could only apply to this situation if it were somehow altered, for example: if all employees were informed, upon being hired, that "Ted is allowed to wear jeans" because of his relationship with the company's founders. In this way it is implied that none of the rest of them may be allowed (as a universal rule to which Ted is the stated exception) to wear jeans in the workplace.

If the original meaning of the phrase is preserved along with the original example of Ted, it will not fit. The simple fact that Ted is an exception (that an exception exists at all) proves that the statement about company employees is not a rule, it is merely a trend.

Another example, if it is common place for a nurse that is male to be described as "a male nurse", it could be taken as evidence to a rule of thumb that most nurses are female.

Jocular nonsense[edit]

It is also used in jocular nonsense. "I am always punctual." "Were you on time for breakfast this morning?" "Well no, but the exception proves the rule." In this case, the first speaker is aware that the phrase does not correctly apply to his or her initial statement, but is appealing to it ironically.

Serious nonsense[edit]

"It will rain on my birthday, it always does."
"It didn't rain last year."
"But the exception proves the rule."

The first speaker in this example has confused the meaning of the phrase, apparently believing that any exception to any rule "proves" the rule true; in this case, the notion that "the exception proves the rule in cases not excepted" is neither implied nor understood by the speaker.


Fowler writes "The last of these is the only one that need to be objected to directly, though 3 & 4 bear the blame of bringing 5 into existence." Fowler objects to the misuse of this proverb because it implies the following two beliefs:

  • Exceptions can always be neglected.
  • A truth is all the truer if it is sometimes false.

It was in objection to this misuse that Arthur Conan Doyle had his famous detective Sherlock Holmes utter the statement "I never make exceptions. An exception disproves the rule."[5]

Lexicographer Bryan A. Garner describes Fowler's entry on the phrase as "all but incomprehensible.”[2]

Other interpretation[edit]

Giving an opposite reading to that above, Mark Forsyth claims in his book The Etymologicon that the "prove" in the expression comes from the Latin probare, meaning not so much to show as true as to test (as in proving-ground), and thus that "the exception that proves the rule" is a (prima facie or seeming) exception to a rule or hypothesis which tests whether or not the rule holds in all cases.[6] This echoes the satirical explanation by Ambrose Bierce in the latter's Devil's Dictionary (s.v. exception):

Exception, n. A thing which takes the liberty to differ from other things of its class, as an honest man, a truthful woman, etc. "The exception proves the rule" is an expression constantly upon the lips of the ignorant, who parrot it from one another with never a thought of its absurdity. In the Latin, "Exceptio probat regulam" means that the exception tests the rule, puts it to the proof, not confirms it. The malefactor who drew the meaning from this excellent dictum and substituted a contrary one of his own exerted an evil power which appears to be immortal.

As an example, during the 2012 Webby Awards, actor Richard Dreyfuss chose to honor Steve Jobs by calling him an "Exception that proves the rule.” In the context of Jobs's success as CEO of Apple, this use could be understood to say that his performance or approach called the rule (i.e., the approaches of other companies) into serious question.

See also[edit]


  1. ^ "Full Definition of PROVE". Merriam-webster. Retrieved 17 June 2015.
  2. ^ a b The Oxford Dictionary of American Usage and Style, p. 138, Bryan A. Garner
  3. ^ phrases.org.uk
  4. ^ The exception proves the rule Archived 2008-04-05 at the Wayback Machine, alt-usage-english.org
  5. ^ Arthur Conan Doyle (1890). "The Statement of the Case". The Sign of Four. London: Spencer Blackett. p. 31.
  6. ^ "The exception that proves the rule", The Phrase Finder

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