Anyone who has ever heard a knock-knock joke, a "Little Mary" or "Tom Swifty" story, or a "daffynition" of a common word, has experienced the sometimes groan-inducing form of humor known as a pun. Puns are not always meant to be humorous, but they are meant to be a clever play on words. From a literary standpoint, the art of creating one is also known as paronomasia, although that word has fallen out of favor in modern times. A pun can be constructed in several different ways, based on the meaning or sonics of the words involved. Words could sound alike but have clearly different meanings, like "jeans" and "genes," or they could be spelled the same but have two or more definitions, like the word "club."
A knock-knock joke's humor depends heavily on the use of a pun: "Knock, Knock." "Who's there?" "Orange." "Orange who?" "Orange you going to let me in?" The word orange sounds very similar to the contraction aren't, so the joke is homophonic. Other knock-knock jokes use the double sounds of common words as part of the set-up and punchline. A pun is usually delivered without much fanfare or build-up, but more as a clever quip or quote. This is why most knock-knock jokes are mercifully short.
A good pun often hinges on the duality of meaning found in many words. On the television show "Frasier," the title character hosts a meeting of his somewhat dubious fan club. His brother Niles is introduced to the group, whereupon he quips "After meeting all of you, I sorta wish I had a club myself." The humor comes from the dual meaning of the word club. While Frasier meant it in the sense of a group, Niles cleverly twisted it to imply an actual heavy weapon. The success of the joke largely depends on the subtlety and cleverness of the wordplay. One that is too obvious usually evokes a groan from the audience.
There are a number of famous sayings which use the form of a pun for their humor. President Harry Truman was known to invite people to his home state to sample his wife's cooking, saying "Missouri loves company." Playwright Oscar Wilde was well-known for his use of puns to soften his often caustic observations. Wilde once described work as the "curse of the drinking classes," which cleverly played off the duality of "working classes" and "drinking glasses." Comedian Groucho Marx used to claim he went elephant hunting in Alabama, where the "tusks are looser." This was a play on the similar sounding Alabama city called Tuscaloosa.
A pun can run the gamut from obscure to patently obvious, but better ones tend to survive from generation to generation. Authors from Ambrose Bierce to Jeff Foxworthy to Dave Barry have all created humorous dictionaries based on actual words with fictitious definitions or invented words with real definitions. These collections point out the inherent humor of a well-crafted pun. While some may consider them to be one of the lowest forms of humor, others applaud the ingenuity and command of the language that they display.