glottochronology, the study of the rate of change occurring in the vocabularies of languages for the purpose of calculating the length of time (time depth) during which two related languages have developed independently. Glottochronology rests upon statistical comparison of the basic vocabulary shared by two or more related languages and on the assumption that the rate of vocabulary replacement is constant over sufficiently long periods of time. A number of linguists do not accept the methods or findings of glottochronology, for two reasons: the difficulty of compiling a culturally unbiased basic vocabulary list and the belief that the rate of linguistic change is not the same for all languages and is not constant for any single language.