A joke of the first order was told to a Scotchman, who was unable to see it.  The person (X) who told this joke told the story of how the joke was received to another Scotchman, thereby making a joke about a joke of the first order, and thus making a joke of the second order.  X remarked on this joke that no joke could penetrate the head of the Scotchman to whom the joke of the first order was told, even if it were fired into his head with a gun.  The Scotchman, after severe thought, replied:  "But ye couldn't do that, ye know!"  X repeated the whole story, which constituted a joke of the third order, to a third Scotchman.  This last Scotchman again, after prolonged thought, replied; "He had ye there!"  This whole story is a joke of the fourth order.<p><pre><code>  (from "The Philosophy of Mr. B*rtr*nd R*ss*ll", by Philip Jourdain)</code></pre>