When people say I could care less, they usually mean they actually could not care less, or, more precisely, that they don’t care. Considered logically, being able to care less means one does care to some degree, while being unable to care less means one cares very little if at all.
Could care less is seldom heard outside the United States, and commentators from outside North America tend to express bafflement over its existence, but it is so common in the U.S. that it is now a widely accepted idiom, meaning that it does not have to be logical. We know what it means even if the words do not literally convey that meaning. English is full of similarly illogical phrases that add color to the language. Many face resistance at first before eventually gaining acceptance.
This is not to say that the people who grouse over the illogic of could care less are wrong, nor are we saying that the phrase is appropriate in formal writing or that it’s better than couldn’t care less (which is in no danger—it remains the more common expression even in the U.S.). But the phrase is entrenched in the language and isn’t going away, so we might as well get used to hearing it.
Could care less is only somewhat new. Historical Google News searches uncover numerous examples from as long ago as the 1950s. Of course, that could care less is over half a century old doesn’t make it less annoying to those who dislike it, but it does support the idea that the phrase is an established idiom.
If we were to read these examples literally, we might think those who “care less” care a lot more than they really do:
I could care less if Charlie Sheen is rushed to the hospital for nearly overdosing on whatever drug he is taking now. [Times and Transcript]
Players see the hunger for acknowledgement, which they interpret as weakness. Tony could care less. [Sydney Morning Herald]
Not having a drop of Irish blood in me, I could care less about the Emerald Isle. [Screen Junkies]
And in contrast, in each of these examples, couldn’t care less literally reflects the writer’s intended meaning:
At the level of semantics, I couldn’t care less what label is applied to economics. [National Review Online]
To be honest, I couldn’t care less what the acting assistant head of Current Affairs said to the assistant acting head of News. [Daily Mail]
But Scott, in his simple, direct manner, makes it clear he couldn’t care less about any of it. [Herald Sun]