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“Is the old maxim true about there being an exception to every rule? Well, no doubt we can all think of rules that appear to have no exceptions, but since appearances can be deceiving, maybe the old maxim is true. On the other hand, the maxim is itself a rule, so if we assume that it’s true, it has an exception, which would be tantamount to saying that there is some rule that has no exception. So if the maxim is true, it’s false. That makes it false. Thus we know at least one rule that definitely has an exception, viz., ‘There’s an exception to every rule,’ and, although we haven’t identified it, we know that there is at least one rule that has no exceptions.”

— David L. Silverman, Word Ways, February 1972

Raymond Smullyan used to send emails to friends that read, “Please ignore this message.”

“I don’t like writers who are making sweeping statements all the time. Of course, you might argue that what I’m saying is a sweeping statement, no?” — Jorge Luis Borges, quoted in Floyd Merrell, Unthinking Thinking, 1991