He is noted for developing the Process Theory of Language (言語過程説, gengo katei setsu) and his criticism of Ferdinand de Saussure.
[1] In his early years, he was already interested in the Japanese language and resolved to devote his life's work on this field.
[5] Tokieda's theory also criticized Yoshio Yamada's position that kokugogaku should only refer to studies done by Japanese people on their own language and exclude those undertaken by foreigners.
[6] According to Tokieda, the difference in terms of research conducted by the Japanese and foreign scholars rests on the used approaches and that one cannot say one is kokugogaku and the other is not.
[6] Tokieda also stressed that the concept of kokugo must not be defined as the language of the Japanese Empire but as one that it is based on its internal linguistic characteristics.