I'd except Kierkegaard's ruminations, but otherwise basically agree with
Marcus's point about formal thinking not allowing much room for humor.
And that was my initial point about Mark Twain's HUMOR as opposed to his
satire. Let me repeat, his humor is often deep, but by definition it is
not serious. Humor is an attitude, a suspension of directed and
meaningful action (that is to say, seriousness) in order to appreciate
incongruity. Satire may arise from humor, but when it does, it tries to
move the intial humorous perception--which is ethically neutral--to
confirm an ethical position. Satire is a species of rhetoric; humor is
not. Twain raised satire to an art, but I prefer the even higher level to
which he raised humor, I think.
Given recent responses to plugging one's own work here, I hesitate to say
that I've written a fair amount on humor's structure, functions, etc. in
the concluding chapter to _Necessary Madness: THe Humor of Domesticity in
19th-c. American Literature_ (Oxford: 1997), but I'll risk the flames.