The logical rigor of English

In the U.S. the phrase "could care less" is used to mean "don't care at all." In the U.K., however, people say "I couldn't care less" to mean the same thing. Logically speaking, to say "I could care less" to mean "I don't care" like Americans do is a bit bizarre, because the sentence would normally be deemed as a truncated version of "I could care less than I do now," which would imply "I do care to some extent."

Just think of the sentence "I couldn't agree more." Everyone understands that it means "I completely agree," being a shortened version of "I couldn't agree more than I do," which implies the speaker agrees to the largest degree. If you follow this reasoning and apply it to "could care less," the phrase should mean "I care to some extent" and if you want to say you just don't care, you should use "couldn't care less."

Strangely, quite the reverse happens in the U.S. But this phenomenon is not limited to the "could care less" construction. For example, some point out that Americans tend to say "cannot underestimate X" to mean that the value or degree of X is very great. But the verb "underestimate" basically means to estimate the value of something to be lower than it really is. If so, the phrase "cannot underestimate X," which should mean "cannot estimate the value of X to be lower than it really is," would imply that the value of X is extremely low, and if you wanted to say the value of X is great, you would have to change "underestimate" into "overestimate." But this is not necessarily the case, at least when it comes to American English.

What makes these somewhat bizarre constructions all the more interesting is that their original (or logically tenable) versions like "couldn't care less" and "cannot overestimate" are the ones Japanese learners of English have great difficulty mastering. Indeed, typical Japanese, when they first come across, say, the phrase "cannot overestimate X," tend to think it implies the value of X is very low.

I did make the same mistake when I was a high school student and, reading in a grammar a logical explanation of why the meaning of the phrase was diametrically opposed to what I had expected it to be, was impressed with the logical rigor with which native speakers of English understood such constructions. But I must have overestimated their logical reasoning.

The fact that Americans do make the same "mistake" as typical Japanese learners do or, in other words, the fact that they can interpret sentences like "cannot underestimate" and "could care less" in the same way as Japanese learners do suggests that native speakers do not necessarily, even unconsciously or implicitly, follow logical rules when they speak.

In fact, when I asked a friend of mine (a native) about the phrase "could care less," she said that to say "could care less" to mean "just don't care" was only natural and not until I reminded her of how "couldn't agree more" is usually understood in English did she realize that it (could care less) was unreasonable at least from a logical point of view.

Of course, I have no intention whatever of criticizing Americans for being illogical. But what I could care less about saying is that you cannot be too careful of overestimating the logical rigor of English or its speakers.