Exception paradox

In the exception paradox, the statement "every rule has an exception" leads to a contradiction.
The argument
# Every rule has an exception.
# "Every rule has an exception." is a rule.
# 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
* If everything is possible, then it is not 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

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