present (or, for that matter, from the common noun “a bet”). - the verb is not a compound, like “overpay” or “unbind”, as the effect of the underlying verb (“pay”, “bind”) is presumably stronger than that of usage frequency. We therefore obtain a list of 106 verbs that we use in the study (marked by the denomination ‘True’ in the column “Use in the study?”) III.5B. Verb frequencies Next, for each verb, we computed the frequency of the regular past tense (built by suffixation of ‘-ed’ at the end of the verb), and the frequency of the irregular past tense (summing preterit and past participle). These trajectories are represented in Fig 3A and Fig S8. We define the regularity of a verb: at any given point in time, the regularity of a verb is the percentage of past tense usage made using the regular version. Therefore, in a given year, the regularity of a verb is r=R/(R+l) where R is the number of times the regular past tense was used, and | the number of times the irregular past tense was used. The regularity is a continuous variable that ranges between 0 and 1 (100%). We plot in Figure 3B the mean regularity between 1800-1825 in x-axis, and the mean regularity between 1975-2000 in y-axis. If we assume that a speaker of the English language uses only one of the two variants (regular or irregular); and that all speakers of English are equally likely to use the verb; then the regularity translates directly into percentage of the population of speakers using the regular form. While these assumptions may not hold generally, they provide a convenient way of estimating the prevalence of a certain word in the population of English speakers (or writers). III.5C. Rates of regularization We can compute, for any verb, the slope of regularity as a function of time: this can be interpreted as the variation in percentage of the population of English speakers using the regular form. By holding population size constant over the time window used to obtain the slope, we derive the vari