This led him to begin studying linguistics with Edward Sapir at Yale University while still maintaining his day job at the Hartford Fire Insurance Company. During his time at Yale he worked on the description of the Hopi language, and the historical linguistics of the Uto-Aztecan languages, publishing many influential papers in professional journals. He was chosen as the substitute for Sapir during his medical leave in 1938. Whorf taught his seminar on "Problems of American Indian Linguistics". In addition to his well-known work on linguistic relativity, he wrote a grammar sketch of Hopi and studies of Nahuatl dialects, proposed a deciphering of Maya hieroglyphic writing, and published the first attempt towards a reconstruction of Uto-Aztecan.