"I don't stay up nights worrying," said John Lennon in 1965. "Summers I used to cover Missouri," wrote Thornton Wilder in 1934. "I went over there afternoons," wrote Ernest Hemingway in 1929.

Why do we sometimes use nouns — "nights," "summers" and "afternoons" — as adverbs like this? In fact, this usage is a linguistic fossil, a remnant from the early history of English.

Today we use the genitive case of a noun to indicate possession, as in "night's coolness" or "summer's warmth." But in Old English, the genitive case could also indicate that a noun or adjective was being used as an adverb.

In Old English, the genitive was formed by adding "-es" to a word. (It wasn't until the 1600s that printers started replacing the "e" with an apostrophe.)

So the genitive of the Old English adjective "daeg" (day), for instance, was "daeges," which had not only the possessive meaning "of the day," but also the adverbial meanings "during the day," "on the day" and "what happens in daeges, stays in daeges."

(A "missing link" between the possessive genitive and the adverbial genitive can be found in archaic adverbial phrases, such as "of a day" ("during the day") and "of nights" ("during the nights"). William Shakespeare uses the latter construction when his character Julius Caesar praises "fat, sleek-headed men . . . such as sleep o' nights.")

Adverbial genitives, though lean and hungry, still survive in modern English. That's why we say, "I work days," meaning "I work by day," as well as "I leave early most Saturdays," "Winters I go to Florida," and "Sunday mornings I like to sleep late."

This practice of adding an "s" sound to a noun or adjective to indicate its use as an adverb also lives on in the non-standard folk formations "somewheres," "anywheres" and "nowheres," and in standard adverbs such as "nowadays," "unawares," "sideways," "backwards," "onwards," "upwards," "afterwards" and "towards."

Those last five "-ward" words were formed by tacking on the suffix "-es" to the Old English adjectives "backweard," "onweard," "upweard," "afterweard" and "toweard," and both forms of these words still survive — "backward/backwards," "upward/upwards," etc.

Other ghosts of the adverbial genitive are "once," "twice" and "thrice." In these words the modern "-ce" spelling reflects the original "-es" spelling.

One last question: If John Lennon didn't stay up nights worrying, why did he sing about "a hard day's night"?

Rob Kyff, a teacher and writer in West Hartford, Conn., invites your language sightings. Send your reports of misuse and abuse, as well as examples of good writing, via e-mail to [email protected] or by regular mail to Rob Kyff, Creators Syndicate, 5777 W. Century Blvd., Suite 700, Los Angeles, CA 90045. To find out more about Rob Kyff and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.