Western historians researching the Edo Period in Japan face a number of seemingly insurmountable hurdles. First, there is the language, notoriously difficult to master, with classical Japanese in early documents even harder. Second, there is a paucity of accessible primary sources, in some part due to the desire of the great feudal families to keep their family archives ‘sacred’ or secret [the words are the same in Japanese]. Obtaining permission usually involves the right letter of introduction by someone in the family’s circle and the kind of traditional Japanese manners, in making the approach, that have gone out of fashion. I am probably one of the few Japanese of my generation who still write letters using traditional brushstroke calligraphy. Even with permission granted, one invariably finds the archives are neither designed nor staffed to handle scholars’ enquiries.

Compounding this, and of course related, is the tendency of even the most respected Japanese historians not to reveal their sources. Naturally, therefore, publications that contain ‘new’ information without documentary evidence arouse suspicion among those steeped in the Western traditions of scholarship. And yet, in my experience, these accounts are often the product of extensive research.

Much of this research is conducted at the local level, typically on local government records, at libraries and temples, with local historians, amateur and professional, and at historical sites. In some ways, Japan is highly centralized in the way it is governed, but information is maddeningly decentralized. Well-researched history books often have small print runs, whether out of modesty or a determination to keep things local, I do not know. There is of course no centralized national reference library, like the British Library or the Library of Congress in the USA.*354 In the book, I describe how William Adams was the first to introduce the sweet potato into Japan. In fact, the Satsuma clan found the potato first, but typically kept the information [and the potatoes!] to themselves.

The question of precise authorship of official records at that time is also opaque. At Nikko Tosho Gu and Sanko Library, one of the few family archives open to scholars, no-one can or will tell you whether a particular record was written by Ieyasu himself, or a close retainer, or anyone else.