“It gets you to think harder about the motivation for change,” says Salikoko Mufwene, from the University of Chicago. “The general claim is that there has been an evolution toward regularization, and they’re showing that this hasn’t always been the case. Now we need to think harder about when irregular forms are favored over regular variants.”
That is, if anything is favored at all. The team found that the changes that have befallen the vast majority of our verbs are entirely consistent with drift. You don’t need to invoke natural selection to explain why we say spilled instead of spilt, burned instead of burnt, and knit instead of knitted.
In other cases, drift and natural selection work together to shape languages. For example, Plotkin’s team also looked at the rapid rise of do in the 16th century, when phrases like “You say not” quickly changed into “You do not say.” They concluded that at first, the word randomly drifted its way into questions, so that “Say you?” gradually became “Do you say?” Once it became common, natural selection started pushing it into new contexts like declarative sentences, perhaps because it was easier for people to use it consistently.
The team also analyzed a third and more obscure grammatical change called Jespersen’s Cycle. In Old English, spoken before the Norman Conquest, speakers would negate a verb by putting a not in front of it. In Middle English, spoken between the 11th and 15th centuries, the negatives would surround the verb as they do in modern French (“Je ne dis pas”). And in Early Modern English, spoken between the 15th and 17th centuries, the negative followed the verb—the Shakespearean “I say not.” Now, we’ve come full circle, back to “I don’t say.”
Jespersen’s Cycle exists in many unrelated languages. In French, for example, the formal “Je ne dis pas” is giving way to the colloquial “Je dis pas.”
Natural selection still explains Jespersen’s Cycle far better than drift does, according to Plotkin's analysis. Perhaps it’s due to emphasis, he says. If one form is common, speakers could emphasize their disagreement by adding or subtracting words (“I don’t say that at all,” versus “I don’t say that”). As the emphatic forms become more common, they lose their sting, and are themselves replaced.
These results are part of a wider trend where linguists are starting to use these massive online corpora to address long-standing puzzles in language change. “This is an excellent trend,” says Jennifer Culbertson, from the University of Edinburgh. “Linguists have uncovered many really fascinating cases of language change, but the explanations on offer sometimes read like just-so stories. Random processes are simply underappreciated, because we want to come up with interesting explanations.” But by considering drift, too, linguists could “focus our energies on providing interesting explanations where they are really warranted.”
What about the change from clearness to clarity, which set Plotkin onto this quest in the first place? He says that he’s found signs of natural selection’s hand, but that will have to wait for another publication. “There’s lots to be done,” he says. “This is just the beginning of an investigation, which need not stop at written texts. Spoken records are just as ready and ripe for scrutiny.”