No, that’s not the four-letter word in decline. It’s “ain’t.”
Unlike other proscribed four-letter words, “ain’t” isn’t obscene, blasphemous, or insulting. And yet in its heyday, not too long ago, in some circles it could provoke a reaction even stronger than the f-word.
What reaction? Well, according to one version of the jump-rope rhyme:
Don’t say ain’t or your mother will faint,
your father will fall in a bucket of paint,
your sister will cry, your brother will die,
your dog will call the FBI.
Why? Well, according to another version of the rhyme,
Don’t say ain’t, your mother will faint,
your father will step in a bucket of paint,
because there ain’t no word such as ain’t.
So proscribed was “ain’t” that like other four-letter words having to do with certain intimate activities, supposedly it wasn’t in the dictionary. And if it wasn’t in the dictionary, it wasn’t a word.
(Digression: It’s an interesting view of language, the notion that dictionary precedes usage. It provides an explanation for the origin of language: cave-dwelling proto-humans waiting mutely for the lexicographer to come by with a book of words. But that’s off the topic here.)
Back in the day, one little “ain’t” could express everything antiestablishment and countercultural. It also expressed strong emotion, the notion that the speaker was so overcome with feelings that he or she forgot his or her proper grammar. “Ain’t” was down to earth and sincere. Hence the down-to-earth love songs employing “ain’t.”
“Ain’t” had the advantage over other four-letter words in being pure defiance or pure sincerity, not carrying any baggage of obscenity, blasphemy, or indeed any other content at all, since it is just a form of “be” or “have.” So it was particularly useful for anyone cursed with a sheltered proper middle-class upbringing, untutored in nonstandard language or vulgar vocabulary. All that was needed to signal defiance or sincerity was a single “ain’t.”
The height of “ain’t”s salience as a marker of attitude came with the publication of Webster’s Third New International Dictionary, Unabridged, in 1961, where it served as the primary scapegoat for lexical “permissiveness.” The inclusion of “ain’t” in what had long been regarded as “the dictionary,” with its infamous equivocation about propriety (“though disapproved by many and more common in less educated speech, used orally in most parts of the U.S. by many cultivated speakers esp. in the phrase ain’t I”), led many guardians of the language to denounce the Third and rely on the Second, where “ain’t” was listed but restricted as slang and nonstandard.
Alas, those days are no longer with us. Most if not all of the other four-letter words have been let loose from their cages, and none of them has the shock value they did when they were unfit for polite company. We hear and read a much greater variety of language nowadays than we did then.
Back in 1961, you could shock people by wearing torn jeans on an airplane, to a symphony concert, or even to go shopping downtown. Nowadays it’s whatever. And the same with “ain’t.” It just ain’t what it used to be.