1. Although everyone understands humour, it's hard to explain what it is.
2. Or rather impossible, as observed by actual comedians and comedy writers.
3. Despite which, there have been a number of academic attempts to theorise humour.
4. For that which is inexplicable has tended to attract more enthusiasm than that which can.
5. So for 2000 years, it's been assumed that all forms of humour may have a common ingredient.
6. The search for this ingredient was occupied mainly by philosophers, and psychologists thereafter.
7. Superiority theory, the oldest, by Plato, holds humour as that which comes from the misfortune of others.
8. Relief theory, made famous by Sigmund Freud, holds humour as that which releases tensions and inhibitions.
9. Incongruity theory, by Hegel, Kant, Schopenhauer, holds humour as the result of a sudden shift in perspective.
10. Resolution of incongruity theory, its variant, holds humour as an unexpected solution from a shift in perspective.
11. Benign violations theory, by Thomas Veatch, holds humour as harmless violations of social, moral, physical norms.
12. Play theory, by Max Eastman, holds humour as a kind of pleasure that's drawn from playful presentations of pain.
13. Conflict theory, by Karl Marx, holds humour as that which acts as an expression of conflict, struggle or friction.
14. Ambivalence theory, by Louis Joubert, holds humour as that which is an inside battle between opposing emotions.
15. Dispositional theory, by Dolf Zillmann and Joanne Cantor, holds humour as that which is derived from antipathy.
16. Gesalt theory, by Max Wertheimer, holds humour as that which comes via tweaked meaning that change meaning.
17. Piagetian theory, by Jean Piaget, holds humour as that which derives pleasure from taking things out of place.
18. Configurational theory, by Paul Schiller, holds humour as that which arises from interpretations, not what it is.
19. But most theories are versions of incongruity theory, which is the most plausible account on what makes humour.
20. Since humour perpetuates unresolvable gaps in reason, gaps in theorist resolutions can be framed as deliberate.
21. By this antilogic, as the cartoonist Ben Juers notes, all theories prank the writer/reader, while missing the point.
22. Or as E. B. White puts, 'Analysing humour is like dissecting a frog. Nobody cares and the frog dies in the process.'