CHICAGO Irregular verbs are the bane of any effort to learn English, but new research looking at how language evolves suggests frequent use keeps pesky irregular verbs like "take" from evolving into "taked."
The research, published on Wednesday in the journal Nature, suggests that frequent use -- in many languages, not just English -- gives words their staying power.
It's a linguistic use it or lose it rule.
"The top 10 verbs in the English language are all irregular, even though irregular verbs make up only 3 percent of the language," said Erez Lieberman, a graduate student in applied mathematics at Harvard University's Program for Evolutionary Dynamics.
The 10 most commonly used verbs in English are the irregular verbs to be, to have, to do, to go, to say, to see, to take and to get, plus the auxiliary verbs can and will.
Most English verbs use the standard -ed ending when forming the past tense. Lieberman believes this rule won an evolutionary battle of the fittest.
"There are these six other rules (for forming the past tense) that existed 1,200 years ago that died," he said in a telephone interview.
"Irregular verbs are the fossils of these six dead rules. When a rule emerges, it emerges by killing off the others," he said, adding, "Frequency is the armor against the -ed rule."
Lieberman said this frequency theory has been long held by linguists, but he and colleagues set out to prove it mathematically.
They undertook an exhaustive study of irregular verbs to find out which verbs have succumbed to the -ed rule.
Of the 177 irregular verbs that existed 1,200 years ago, 145 survived into Middle English and just 98 remain today.
With this database and frequency data, they arrived at a formula that predicts the half-life of irregular verbs -- much like the half-life of a radioactive atom.
As it turns out, the rate at which an irregular verb decays is inversely proportional to the square root of how frequently it is used. So, a verb used 100 times less frequently will evolve 10 times as fast.
WEDDED BUT NOT THINKED
Based on this model, Lieberman and colleagues predict some other words will soon conform to the -ed rule.
First up will be the verb "to wed." He predicts couples will soon be "newly wedded" and not "newly wed."
Favorite verbs like "to be" will likely survive unchanged for another 38,000 years while "to think" has 14,400 years before "thought" becomes "thinked."
The frequency rule appears not to be restricted to irregular verbs, however.
In a separate paper, Mark Pagel of the University of Reading and colleagues used a statistical modeling technique to analyze four languages: English, Spanish, Russian and Greek.
They compared this to a database of 200 fundamental vocabulary meanings in 87 languages and found that across all 200 meanings, commonly used words evolve much more slowly.
"The words that change the most slowly include numbers, pronouns and special adverbs," Pagel said in e-mailed comments.
"These all seem to carry lots of meaning, whereas conjunctions and prepositions, which evolve rapidly, often act as place holders," he said.
The reason may be that when a word is common, "...we are more likely to be 'corrected' by hearing someone else speak."
Pagel said the findings help us understand why languages seem to resist change.