Okay, on suggestion of a friend, I read this article....
JOKES and the Logic of the Cognitive Unconscious
by Marvin Minsky, MIT
Abstract: Freud's theory of jokes explains how they overcome the mental "censors" that make it hard for us to think "forbidden"
thoughts. But his theory did not work so well for humorous nonsense as for other comical subjects.
In this essay I argue that the different forms of humor can be seen as much more similar, once we recognize the importance of knowledge about knowledge and, particularly, aspects of thinking concerned with recognizing and
suppressing bugs -- ineffective or destructive thought processes.
When seen in this light, much humor that at first seems pointless, or mysterious, becomes more understandable.
Introduction ============
A gentleman entered a pastry-cook's shop and ordered a cake; but he soon brought it back and asked for a glass of liqueur instead. He drank it and began to leave without having paid. The proprietor detained him.
"You've not paid for the liqueur." "But I gave you the cake in exchange for it." "You didn't pay for that either." "But I hadn't
eaten it". --- from Freud (1905).
We work to discover "islands of power" within which commonsense reasoning seems safe.
We work also to find and mark the unsafe boundaries of those islands.
Source