During the Three Periods,the validity and the point emphasized by
the orthodox calendar was mainly the substituted pre-dynasty.It
began to change in mediaeval times.The validity focus incarnated by
the orthodox calendar had turned from the pre-dynasty to other countries.First of all,the orthodox calendar was the
institution and the behavior,while it did include a concept and an intent.In this way,the orthodox calendar derived a notion from the primary institution gradually.This was “the theory of legitimacy”.The signification of “the theory of legitimacy”was originated from ancestry.Originally “the theory of legitimacy”was the provision of the convenance institutions,not the political idea.The political practice as the patriarchal clan system and the stylistic rules in the history records as the ethical conception were dissimilar.The division between them really couldn’t be ignored or obliterated.If we called the latter“the theory of legitimacy”,we should name the former “the institution of legitimacy”.