Predicting How Verbs Evolve

October 29, 2007

Applying evolutionary models, Harvard mathematicians and researchers hypothesize that irregular English verbs "evolve" at a rate that is inversely proportional to their prevalence. In other words, less frequently used verbs will change faster.

Irregular verbs that do not take an "-ed" ending in the past tense are subject to powerful pressure to "regularize" as the English language develops. "Mathematical analysis of this linguistic evolution reveals that irregular verb conjugations behave in an extremely regular way — one that can yield predictions and insights into the future stages of a verb's evolutionary trajectory," said Erez Lieberman, a graduate student in applied mathematics at Harvard. "We measured something no one really thought could be measured, and got a striking and beautiful result."

To come to their startling conclusion, the researchers tracked the status of 177 irregular verbs in Old English through linguistic changes in Middle English and then in modern English. Of the verbs that were irregular more than 1,000 years ago, 145 stayed irregular through Middle English but fewer than 100 are irregular today, following the regularization over the centuries of such verbs as help, laugh, reach, walk, and work.

In general, irregular English verbs decay (or become regularized) at a rate that is inversely proportional to the square root of their usage frequency.

The researchers computed the "half-lives" of the surviving irregular verbs to predict how long they will take to regularize. The most common ones, such as "be" and "think," have half-lives of many thousands of years, making them effectively irregular forever. The calculations suggest that the next word to regularize will be "wed."

"Now may be your last chance to be a 'newly wed'," the researchers quipped in their paper, "Quantifying the Evolutionary Dynamics of Language," published in the Oct. 11 Nature. "The married couples of the future can only hope for 'wedded' bliss."

The predictions confirmed what linguists have suspected for a long time: The most frequently used irregular verbs are repeated so often that they are unlikely to ever go extinct. "Irregular verbs are fossils that reveal how linguistic rules, and perhaps social rules, are born and die," said Jean-Baptiste Michel, who is in Harvard's Program for Evolutionary Dynamics.

"If you apply the right mathematical structure to your data, you find that the math also organizes your thinking about the entire process," Lieberman said. "The data [haven't] changed, but suddenly you're able to make powerful predictions about the future."

Source: Harvard University, Oct. 10, 2007.