Among Sethe's many contributions to Egyptology, two are singled out by Gardiner (p. 433): "...the pronunciation of Middle Egyptian... The chief authorities to be consulted are Sethe's great work on the Egyptian verb, and a much later brilliant article entitled Die Vokalisation des Ägyptischen in Zeitschrift der deutschen morgenländischen Gesellschaft"" (1923). Actually, Sethe was the first one to put forth a systematic theory of the Egyptian verb; it was no easy accomplishment, since the inflection of the Egyptian verb was done mainly by changing the vowels, and the Egyptians only wrote consonants.
