This work investigates the evolution of the Japanese language from its earliest recorded forms to the development of the modern vernacular. George Sansom, a renowned historian and diplomat with extensive expertise in Japanese culture, utilizes primary source texts and classical literature to reconstruct the linguistic shifts that occurred over centuries. The book provides a rigorous framework for understanding the morphological and syntactical changes that define the transition from Old Japanese to the language used in the early twentieth century.

Scholars and linguists frequently cite this text as a foundational reference for the study of Japanese philology. Readers often note the academic density of the prose, which requires a high level of familiarity with linguistic terminology and the Japanese writing system.