Exception paradox

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In the exception paradox, the statement "every rule has an exception" leads to a contradiction.

The argument[edit]

  1. Every rule has an exception.
  2. "Every rule has an exception." is a rule.
  3. There is a rule R without exception. (by 1. and 2.)

Since 3. is the negation of 1., there is a contradiction.

From the logical point of view, this can be taken as a proof that the sentence "every rule has an exception" is false - a simple example of a proof technique known as reductio ad absurdum.

Variations on the paradox[edit]

  • If everything is possible, then it is possible for anything to be impossible.
  • The only rule is that there are no rules.
  • The only thing certain is that there is nothing certain. This may be shortened to "Nothing is certain.".
  • "Moderation in all things, including moderation", a quotation sometimes attributed to Petronius.
  • Ignore all rules