. Although there are many hypotheses concerning the “origins” and genetic affiliations of Japanese/Japanic, it appears that the diachronic information inherent in the Japanese language material itself is still insufficiently understood. A potential clue to Pre-Proto-Japanic language typology is offered by the Japanese morpheme structure, which, when analyzed in a framework of internal reconstruction, reveals a striking predominance of simple monosyllabic roots with tonal distinctions. In addition to the numerous monosyllabic stems of the types (C)V(C) still present in modern Japanese, a large part of the more complex stems of the synchronic types (C)VCV(C) can actually be shown to be composed of primary monosyllabic components. This suggests that Japanese, very much like Mandarin Chinese on the continent, has evolved from a monosyllabic tonal language of the Sinitic type in the direction of an increasingly polysyllabic and decreasingly tonal language of the Altaic type. The present paper contains a general characterization of this evolutive process, while a more elaborate analysis of selected details will form the subject of separate papers in the future.