邓广铭先生曾经把“职官制度、历史地理、年代学和目录学”作为治史的四把钥匙。这四把钥匙都涉及比较专门的知识,其中尤以年代学最为繁难,不好掌握,但是研究文史最基本的问题就是年代问题。读史书,尤其是读《资治通鉴》这样的编年体的史书,经常看到的是连续的干支记日。干支记 Mr. Deng Guangming once regarded the “official system, historical geography, chronology and bibliography” as the four keys to governing history. These four keys all involve relatively specialized knowledge, among which the chronology is the most complicated and not well mastered. However, the most basic problem in the study of the history of literature and history is the issue of the age. Reading history books, especially the history books of chronological reading such as “Zi Zhi Tong Jian”, we often see successive dry-branch records. Drill notes