One of the characteristic forms of the Shih Chi taken over by Pan Ku in his Han Shu is the short passage of critical appraisal appended to each chapter. Both Pan Ku and Ssu-ma Ch'ien felt free to use these passages to express their personal opinions--sometimes directly and sometimes with subtle indirection—not only on the facts presented in the preceding chapter but also on pressing issues of their own day. Students of the Han Shu refer to these passages as tsan, after the phrase with which they are introduced in that work, tsan yüeh (“In appraisal we say”). These tsan vary in length from a few lines to several pages.
One of the most highly developed of all Pan Ku's tsan is that appended to Han Shu 94, the “Memoir on the Hsiung-nu.” It is a substantial, well-written essay and at over one thousand characters in length, by far the longest in the entire Han Shu. It reveals much about Pan Ku's historical method and also provides us with the key to his attitude toward barbarian management in his own day. Without the understanding provided by the tsan, it is not possible to appreciate fully the implications of the form and organization of the “Memoir on the Hsiung-nu” itself.