Dear Word Detective: How did the phrase “how come” come to mean “why”? How come we needed a longer, less obvious way of saying “why” when we already have the word “why”? Is this a southern colloquialism, or do people everywhere use “how come?” to mean “why”? — Gary Henderson.

Now here’s an interesting coincidence. My wife, Kathy Wollard, just happens to write a weekly newspaper column called “How Come?” in which she answers science questions from inquisitive children (and many adults as well). She is, in fact, even as I write this, hunkered down in the next room, putting the finishing touches on the third “How Come?” book, which will join “How Come?” and “How Come? Planet Earth” (all published by Workman Publishing) in bookstores next fall. And that, kiddies, is how proper product placement is done. Maybe someday she’ll answer a question that has been bothering me for years: Do trees sleep? They must, right? But every time I ask she rolls her eyes and tells me to be quiet.

“How come?” is actually a very interesting phrase. It seems to have been an American invention of the 19th century, although similar forms date back several hundred years in English. The first appearance of “how come” in print dates to 1848, but since that was in Bartlett’s Dictionary of Americanisms and the phrase was described as being common at that time, it is almost certainly older. That was, after all, an age when slang and colloquial phrases were usually avoided, not memorialized, in print.

The basic sense of the verb “come” is, of course, “to move towards, approach” or “to arrive.” One of the specialized, and now archaic, meanings of “come” is “to happen,” as in the phrase “to come to pass,” reflecting the idea of a condition, time or event “arriving” (also found in such uses as “Come next summer, Dwayne Junior had better have a job”). “How,” used as an adverb modifying a verb (such as “come”), means basically “by what means?” or “for what reason?”

The final piece of the puzzle of “how come” is the fact that it is actually an abbreviation of a longer phrase, which, although not known with certainty, was probably “how comes it” or “how does it come,” meaning “how did this (event, condition, etc.) happen to be this way.”

“How come?” is, as you note, essentially synonymous with “why?”, but in popular usage it often serves a slightly different function. “How come?” carries a challenging, more emphatic tone than a simple “why?” would convey (”How come Jimmy never has to wash the dishes?”). Unlike “why,” “how come” strongly suggests that the questioner has already developed an opinion on the situation and has decided that something is not proper or fair.