Number of words: 395

Thanks to the heroic efforts of Tina Tang, who scoured texts for examples, we were able to study the evolution of 177 irregular verbs over the past 1,200 years, from Beowulf to The Canterbury Tales to Harry Potter. We grasped something that no one thought could be measured and obtained striking results. Of the seven rules for conjugating the past tense in Old English, only one has survived. That single extant rule adds an -ed suffix to simple past and past participle forms. Just as genes and organisms undergo natural selection, words— specifically, irregular verbs such as “holp” that do not take an -ed ending in the past tense—are subject to powerful pressure to “regularize” as the language develops.

Of the 177 verbs that were irregular 1,200 years ago, 145 stayed irregular in Middle English. Only 98 or so remain irregular today, following the regularization over the centuries of such verbs as “help,” “laugh,” “reach,” “walk,” and “work.” What’s striking is that the “decay of an irregular word” followed a very clear trend with remarkably small error bars. The mathematical function explaining this decay says that a verb used 100 times less frequently will regularize 10 times as fast. To put it another way, verbs evolve at a rate inversely proportional to the square-root of their prevalence in the English language. An irregular verb that occurs less often will be forgotten faster. In this way, irregular verbs behave in just the same way as radioactive atoms and have half-lives. We can calculate the half-life of irregular verbs depending on their frequency.

The present tense of “I know” has the irregular past tense “I knew.” Although little kids might apply the logic of language to say—quite understandably—“I knowed,” this verb hasn’t regularized yet. “I know” is so common that it resists change. Children also start out by saying “growed” before they learn the -ew rule. Or “hitted” instead of “hit”—the basis of that old joke—Child: “Mummy, Bobby hitted me. Mother: “Bobby hit me.” Child: “You too? Boy, that kid is in trouble.”

Children need to hear the irregular form often enough to memorize it. As a corollary of this, relatively less popular words are more likely to succumb to change. And all modern verbs, such as “to google,” are regular.

Excerpted from page 194-195 of ‘Super co-operators ’ by Martin Nowak