I have been thinking about this book for a long time. Its inception goes back to 1950, when I began seriously to study the T'ang period, and the necessity for the closest possible critical examination of its rather meager sources became an everyday preoccupation. Later, like that of all historians of China of my generation, my interest in historiographical problems was greatly stimulated by the Conference on the Historians of China and Japan held at the School of Oriental and African Studies in London during the summer of 1956, one of the first, and still one of the best, of the specialized research conferences that have played such an important part in our academic life.

But, although I wrote some short studies on historiographical themes in the 1950s, the focus of my attention turned to other historical problems. I returned to the study of historiography largely through an invitation to contribute to the Yale Seminar on Chinese and Comparative Historiography organized in 1970 and 1971 by my dear friend the late Arthur Wright. A short preliminary outline sketch for part of this volume, entitled “Some Notes on the Compilation of the T'ang Dynastic Record,” was written in his gracious home at Sachem's Head and was one of the two papers I contributed to that stimulating seminar.

Once again the pressures of other work distracted me from taking this study farther, and even from publishing my preliminary survey.