The existence of /tɬ/ in Nahuatl had puzzled previous linguists and caused Edward Sapir to reconstruct a /tɬ/ phoneme for Proto-Uto-Aztecan based only on evidence from Aztecan.
In a 1937 paper[1] published in the journal American Anthropologist, Whorf argued that phoneme was a result of some of the Nahuan or Aztecan languages having undergone a sound change changing the original */t/ to [tɬ] in the position before */a/.
The sound law was labeled "Whorf's law" by Manaster Ramer and is still widely though not universally considered valid, although a more detailed understanding of the precise conditions under which it took place has been developed.
In 1978, Lyle Campbell and Ronald Langacker showed that in fact, Whorf's law had affected all of the Nahuan languages and that some dialects had subsequently changed /tɬ/ to /l/ or back to /t/, but it remains evident that the language went through a /tɬ/ stage.
[2][3] In 1996, Alexis Manaster Ramer showed that the sound change had in fact also happened before the Proto-Aztecan high central vowel */ɨ/, itself derived from */u/ in certain situations and not just before */a/.