I once read that the Greek Philosopher, Chrysippus, died from laughter after he saw a donkey eating some figs. That seemed strange to me until I imagined the scene. To this day, I find donkeys almost unbearably amusing, especially if they are eating. I can't explain it. Something about the donkey's mouth and teeth and the simple donkeyness of it all.
Arthur Koestler had an interesting take on humor. For him, it was produced by what he called "bisociation" - the sudden intersection of two previously unconsidered "planes" of thought.
In Janus, he writes:
[Humor] is the perceiving of a situation or idea in two self-consistent but mutually incompatible frames of reference or associative contexts.
And further on:
The criteria which determine whether a humorous offering will be judged good, bad or indifferent, are of course partly a matter of period taste and personal preference, partly dependent on the style and technique of the humorist. It would seem that these criteria can be summed up under three main headings: (a) originality, (b) emphasis, (c) economy.
The merits of originality are self-evident; it provides the essential element of surprise, which cuts across our expectations. But true originality is not very often met either in humor or in other forms of art. One common substitute for it is to increase the tension of the audience by various techniques of suggestive emphasis. The clown's domain is the rich, coarse type of humor; he piles it on; he appeals to sadistic, sexual, scatalogical impulses; one of his favorite tricks is repetition of the same situation, the same key-phrase. This diminishes the effect of surprise, but helps in drawing emotion into the familiar channel - more and more liquid is being pumped into the punctured pipeline.
Emphasis on local color and ethnic peculiarities - as in Scotish, Jewish Cockney stories - is a further means to channel emotion into familiar tracks. The Scotsman or Cockney must of course be caricatures if the comic purpose is to be achieved - in other words, exaggeration and simplification once more appear as indispensable tools to provide emphasis.
In the highest forms of humor, however, emphasis tends to yield to the opposite kind of virtue: economy. Economy, in humor and art, does not mean mechanical brevity, but the implicit hint of the explicit statement - the oblique allusion in lieu of the frontal attack. The old-fashioned Punch cartoon featuring the British lion and the Russian bear 'rubs it in'; the New Yorker cartoon poses a riddle which the reader must solve be an imaginative effort in order to 'see the joke'.
In humor, as in other forms of art, emphasis and economy are complementary techniques. The first forces the offering down the consumer's throat; the second tantalizes, to whet his appetite.
So, since I have initially emphasized a rather clown-like Chrysippus, I should balance things out with something more economical: my current favorite joke. I came across it in The 100 Funniest Joke of All Time compiled by Don Steinberg for GQ:
Three guys, stranded on a desert island, find a magic lantern containing a genie, who grants them each one wish. The first guy wishes he was off the island and back home. The second guy wishes the same. The third guy says "Im lonely. I wish my friends were back here."
I burst out laughing when I read this. Koestler's bisociation certainly works. But to imagine the third guys expression. And just the pathos of it all. Then, something more essentially human. The condition of abandonment, desolation, forlornity. I think it is a supremely economical joke. It takes no skill to tell; the simple mechanics of humor power it right along. That's amazing to me. And funny as hell.