Glottochronology (from Attic Greek γλῶττα tongue, language and χρόνος time) is the part of lexicostatistics which involves comparative linguistics and deals with the chronological relationship between languages.[1]: 131
The idea was developed by Morris Swadesh in the 1950s in his article on Salish internal relationships.[2] He developed the idea under two assumptions: there indeed exists a relatively stable basic vocabulary (referred to as Swadesh lists) in all languages of the world; and, any replacements happen in a way analogous to radioactive decay in a constant percentage per time elapsed. Using mathematics and statistics, Swadesh developed an equation to determine when languages separated and give an approximate time of when the separation occurred. His methods aimed to aid linguistic anthropologists by giving them a definitive way to determine a separation date between two languages. The formula provides an approximate number of centuries since two languages were supposed to have separated from a singular common ancestor. His methods also purported to provide information on when ancient languages may have existed.[3]
Despite multiple studies and literature containing the information of glottochronology, it is not widely used today and is surrounded with controversy.[3] Glottochronology tracks language separation from thousands of years ago but many linguists are skeptical of the concept because it is more of a 'probability' rather than a 'certainty.' On the other hand, some linguists may say that glottochronology is gaining traction because of its relatedness to archaeological dates. Glottochronology is not as accurate as archaeological data, but some linguists still believe that it can provide a solid estimate.[4]
Over time many different extensions of the Swadesh method evolved; however, Swadesh's original method is so well known that 'glottochronology' is usually associated with him.[1]: 133 [5]