English verbs form the past tense two ways. Regular verbs ad “ed” to the end of the verb. For example, “work” becomes “worked.” Irregular verbs, sometimes called “strong” verbs, require internal changes to form the past tense. For example, “sing” becomes “sang” and “do” becomes “did.”

Irregular verbs are becoming regularized over time. For example, “help” is now a regular verb, though its past tense was once “holp.” (I’ve heard that you can still occasionally hear someone use archaic forms such as “holp” and “holpen.”)

What I find most interesting about this change quantifying the rate of change. It appears that the half-life of an irregular verb is proportional to the square root of its frequency. Rarely used irregular verbs are most quickly regularized while commonly used irregular verbs are the most resistant to change.

Exceptions have to be constantly reinforced to keep speakers from applying the more general rules. Exceptions that we hear less often get dropped over time. So it’s not surprising that half-life is a decreasing function of frequency. What is surprising is that that half life is such a simple decreasing function, a constant over square root.

Source: Quantifying the evolutionary dynamics of language