歷來對孔子所謂「五十而知天命」一句，難有共識。本書透過歷史的與哲學的雙重取向，釐清周初以降，迄至春秋時代，「天命」概念的發展史，同時檢視了孔子個人的生命史，尤其是五十歲前後的轉捩過程，以重現孔子心目中「天命」的特殊義蘊。

從孔子一生行止的大關節來看，本書指出，「五十而知天命」的話語脈絡無疑是針對孔子五十歲左右的「政治的轉向」而言。在這個「政治的轉向」之後，孔子便義無反顧、剛毅而果決地踏上一趟「知其不可而為之」、「行義以達其道」的「踐命」之旅。

For Sang-Yiing Chang, the mandate of Heaven (天命, Tian-Ming) by Confucius is neither a fate nor the mandate from some authority, or from other mysterious and religious Majesty.

Taking both historical and philosophical approaches to investigate the development of its concepts basically upon the original classics; in addition, through the thoughts and life story of Confucius himself, especially during the time of which just before and shortly after the fifties, this Book demonstrates that to Confucius, as a humanist, Tian-Ming is no more a kind of legitimacy from divine approval but one inner mission of Imperative.
The 'political turn' of Confucius in the fifties plays a critical role to understand the real meaning of the words by Confucius: "At fifty, I understood the mandate of Heaven".