The method of glottochronology developed by Swadesh [e.g., Swadesh, M. 1951. “Diffusional cumulation and archaic residue as historic explanations”, Southwestern Journal of Anthropology 7 pp. 1-121] provided a mechanism for ‘decay-dating’. One of its fundamental assumptions was the ‘basic vocabulary’ items (i.e., names of body parts, lower numerals, personal pronouns, basic actions and objects, immediate members of the family, and so forth) would be preserved longer, that is be less subject to decay than non-basic vocabulary, and that about 80% of a two-hundred-word core vocabulary would be preserved over about one thousand years. Time-depth for splits in family relations could therefore be plotted, it was argued, in part according to degree of deviation in core vocabulary. Although severely challenged from the beginning, glottochronology nevertheless seemed valuable as an approximation.
- Traugott (1977), a pag.72