Kogetsusho (The Tale of Genji Moon on the Lake Commentary) is a commentary on The Tale of Genji written by Kigin KITAMURA. It was written in 1673. Sometimes it is called the Genji monogatari kogetsusho.
It has sixty volumes in all. In addition to the fifty-five chapters of The Tale of Genji (due to counting Wakana - Spring Shoots) I and II as well as Kumogakure (literally, vanishing behind the clouds -, the opening part consists of a volume of hottan (origins), a volume of keizu (genealogies), two volumes of toshidate (chronologies) of The Tale of Genji and a volume of hyobyaku (supplications). The name of the 'Kogetsusho' comes from a story where Murasaki Shikibu paid a visit to the Ishiyama-dera Temple one day and she started to write this story from the chapter of Suma after watching the moon over Lake Biwa.
The style of this book is as follows; the book has the whole text of The Tale of Genji, and the author interprets it with interlinear glosses and headnotes.
He not only argues for his own theories, he also explains earlier theories that conflict with his, and he interprets nearly everything starting from the basics.
For that reason, anyone who could read, even if they had no knowledge about The Tale of Genji, would be able to understand it using only this book. Therefore, it was both the text as well as the commentary with the largest circulation during the Edo period.
Even in the period after that, it had such influence that it was said that, 'until the first half of the twentieth century (when academic variorums such as the "Genji Monogatari taisei "were written), it was the age of reading The Tale of Genji using the Kogetsusho.'
For instance, 'Genji monogatari shinshaku' (New Interpretations of The Tale of Genji), a commentary on The Tale of Genji by KAMO no Mabuchi, was written in the form of interlinear glossaries on a printed volume of the Kogetsusho. The Tale of Genji's first translation into modern Japanese by Akiko YOSANO is said to be based upon this Kogetsusho.
The text of The Tale of Genji itself follows the text of proceeding printed books such as the "Eiri Genji monogatari" (Illustrated Tale of Genji) and the "Shusho Genji monogatari" (Tale of Genji with Headnotes).
It is said that although the text is the Aobyoshi-bon, which is the type of Sanjonishike manuscript's shohon (a verified text), the Kawachi-bon and the Beppon (others outside the Aobyoshi-bon and Kawachi-bon lines) also greatly influenced it.
Kogetsusho and the history of commentaries on The Tale of Genji
Kogetsusho is a compilation of the best in the commentaries written on The Tale of Genji during the medieval period. On the other hand, during the early-modern period, kokugaku (the study of Japanese classical literature) rose to prominence and scholars started to review and revise the commentaries. Therefore, the "Kogetsusho" and commentaries before it are called 'kyuchu' (old commentaries) and the "Genchu shui" (Addenda to Commentaries on Genji) written by Keichu, a scholar of Japanese classical literature, and other commentaries afterwards are called 'shinchu' (new commentaries).