英語の不規則動詞は“絶滅”が進んでいた。使う回数がほかの動詞の100分の1なら、10倍の速さで規則動詞に

In English, most verbs take "-ed" in the past tense, like "walked." But some verbs are irregular, like "go" and "went." Researchers at Harvard studied 177 old irregular verbs. About 1,200 years ago, all of them were irregular.

Today only 98 are. Verbs that people use a lot, like "be" and "have," stayed irregular. Rare verbs changed to "-ed" much faster. The verb "help" was once irregular, too.

A team at Harvard University traced 177 irregular verbs from Old English to the present day. In Middle English, 145 of them were still irregular, and today only 98 are. The team found a clear pattern.

Verbs that people use often, such as "be," "have" and "go," have kept their old forms for more than a thousand years. Rare verbs, on the other hand, switched to the regular "-ed" ending much sooner.

A verb used 100 times less often changes about 10 times faster. The researchers even named the next verb likely to change. It was "wed." But a later study of American English found that "wedded" was actually losing to "wed." Language change can go in both directions.

Learners often see irregular verbs as random exceptions, but a 2007 study in Nature found order in the mess. Erez Lieberman and colleagues at Harvard traced 177 Old English irregular verbs that still exist today and checked whether each one adopted the "-ed" ending. Only 98 are irregular now. Using frequency counts from a modern corpus, the team showed that the half-life of an irregular verb is proportional to the square root of how often it is used.

So a verb that appears 100 times less often regularizes about 10 times faster. For "be" and "have," the estimated half-life is around 38,800 years. For the rarest group, which includes "chide," it is about 300 years. A 2014 analysis of American writing from 1830 to 1989 found that "quit," "lit" and "wed" pushed out their regular forms, while "smelled" and "spelled" replaced "smelt" and "spelt."

The overall share of irregular past-tense forms barely moved. The Harvard half-lives depend on rough dates for Old and Middle English, so they are estimates. The thirteen most common verbs in the study, from "be" and "have" to "take" and "think," have not regularized in over a thousand years, so practice them first.