Think about it: When someone says “I couldn’t care less” (or says “I could care less” and means “I couldn’t care less”), how often is the subject at hand truly the one thing that person cares least about in the whole wide world? You might say you couldn’t care less about the color of the dress that the first lady wore to the State of the Union address, but you’d be exaggerating for effect. I could no doubt come up with plenty of things you care even less about— maybe the color of the garment worn by a Bulgarian farm wife you’ve never heard of before and will never hear of again. Conversely and sort of perversely, saying “I could care less” would virtually always be literally true, even if it’s the opposite of what you meant.
Could care less was apparently born in the 1950s. Yes, another baby boomer! Ben Zimmer, the prominent language writer and former dictionary editor, found it in the Washington Post in 1955.
“Couldn’t care less,” interestingly, isn’t much older— Zimmer traces it to 1944. Jan Freeman dug up the earliest known complaint about the variant, a 1960 letter to Ann Landers. Ann sided with the complainer, to the extent that she cared about the issue (yes, she said that extent couldn’t have been less). For the next few decades, those who cared enough to write about the dispute agreed with her verdict, if not her lack of ardor. In his Miss Thistlebottom’s Hobgoblins
(1971), Theodore M. Bernstein of the New York Times bemoaned the “senseless abbreviated form” but observed that it “has not really taken hold.” Bernstein opined that people shorten the expression “because their hearing is defective or because they are in an inordinate hurry, or merely because they think it cute.”
Another Timesman, William Safire, was ready to write an obituary for “could care less” less than a decade later. “Happily,” he said in an On Language column included in a 1980 anthology, the expression “seems to be petering out,” having peaked in 1973. He pointed to the Harper Dictionary of Contemporary Usage, which called it “an ignorant debasement of the language.” (In the same entry, Freeman points out, Isaac Asimov said, “I don’t know people stupid enough to say this.” Ah, those were the days.) Safire concluded: “Farewell, ‘could care less’! You symbolized the exaltation of slovenliness, the demeaning of meaning, and were used by those who couldn’t care less about confusing those who care about the use of words to make sense.”
The eulogy was premature, and writing in the Times in 1983, Safire observed that “the short form is understood and the long form would be regarded as the sort of thing a visiting Martian might say.” But he wasn’t giving up; in the same column, he spun around to venturing that the phrase would atrophy from disuse.