This proposed classification has not been definitively demonstrated, largely because of slow progress in the reconstruction of the intermediate stages of the two language families involved,[1] but is still considered promising by many linguists.

[2][3] The grouping was originally proposed by Edward Sapir in his 1921 classification, but it was not until 1937 that supporting evidence was published by Benjamin Lee Whorf and G. L. Trager.

[4] A recent article by Jane H. Hill argues that the evidence cited for the genetic relation by Whorf and Trager is better understood as a result of language contact between the Uto-Aztecan and Tanoan proto-languages.

[5] The following word pairs are the proposed cognates from Whorf & Trager (1937) and Davis (1979) considered promising by Campbell (1997:273).

Below is a comparison of selected basic vocabulary items in Proto-Uto-Aztecan and Proto-Kiowa-Tanoan.