That is, they developed research on Chinese history focusing on the method dividing the historical ages into four, namely, ancient times up to the Qin and Han dynasties, middle ages up to the Wei and Jin periods in the Northern and Southern Dynasties, and the Sui and Tang periods, recent times from the Northern Song Dynasty and later, and modern times from the Opium War and later.
すなわち、秦漢時代までを上古（古代）、魏晋南北朝時代隋唐時代を中世、北宋以降を近世、アヘン戦争以降を近代とする四時代区分法を中心に中国史の研究を展開した。