Scientific American:

“How Many Psychologists Does It Take ... to Explain a Joke?”

Many, it turns out. As psychologist Christian Jarrett noted in a 2013 article featuring that riddle as its title, scientists still struggle to explain exactly what makes people laugh. Indeed, the concept of humor is itself elusive. Although everyone understands intuitively what humor is, and dictionaries may define it simply as “the quality of being amusing,” it is difficult to define in a way that encompasses all its aspects. It may evoke the merest smile or explosive laughter; it can be conveyed by words, images or actions and through photos, films, skits or plays; and it can take a wide range of forms, from innocent jokes to biting sarcasm and from physical gags and slapstick to a cerebral double entendre.

Even so, progress has been made. And some of the research has come out of the lab to investigate humor in its natural habitat: everyday life.

For more than 2,000 years pundits have assumed that all forms of humor share a common ingredient. The search for this essence occupied first philosophers and then psychologists, who formalized the philosophical ideas and translated them into concepts that could be tested.

Perhaps the oldest theory of humor, which dates back to Plato and other ancient Greek philosophers, posits that people find humor in, and laugh at, earlier versions of themselves and the misfortunes of others because of feeling superior.

The 18th century gave rise to the theory of release. The best-known version, formulated later by Sigmund Freud, held that laughter allows people to let off steam or release pent-up “nervous energy.” According to Freud, this process explains why tabooed scatological and sexual themes and jokes that broach thorny social and ethnic topics can amuse us. When the punch line comes, the energy being expended to suppress inappropriate emotions, such as desire or hostility, is no longer needed and is released as laughter.

A third long-standing explanation of humor is the theory of incongruity. People laugh at the juxtaposition of incompatible concepts and at defiance of their expectations—that is, at the incongruity between expectations and reality. According to a variant of the theory known as resolution of incongruity, laughter results when a person discovers an unexpected solution to an apparent incongruity, such as when an individual grasps a double meaning in a statement and thus sees the statement in a completely new light.

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