This paper examines the changes in deontic expressions in the Tohoku region. By comparing The Grammar Atlas of Japanese Dialects and New Linguistic Atlas of Japan, real-time changes were ascertained. The comparison showed that the use of contractions was widespread throughout the Tohoku region. The contraction of deontic expressions was influenced by the progress of grammaticalization. Glottogram data were analyzed to determine dialectal changes after World War II. There were no major discrepancies with the results of the linguistic map. In the region along the Tohoku-Line, the common language was widely used by the generation born in the 1980s and after, with no dialectal change. However, in the Tsugaru region of Aomori Prefecture, the younger generation continued to use dialectal forms. Even in the areas along the Ou-Line and Uetsu-Line, dialectal forms remained relatively common among the younger generation. A glottogram survey conducted in the southern Tohoku region showed the existence of an intermediate form between the common language and the dialect. The front element was replaced by the common language form, whereas the rear element retained the dialect form. A survey conducted in Miyagi Prefecture suggested that this intermediate form was a dialectal form that was misidentified with the common language. Minutes of local government assemblies revealed that this intermediate form was often encountered in the Miyagi and Iwate prefectures and was relatively common in the Hokkaido and Niigata prefectures. These four prefectures adopted the common language at an early stage, which may have led to the emergence and spread of the intermediate form.