This study tackle the subject of correspondence between ABi Jaf'ar and Mohamad thi annafs alzakiya , when the last one announce the revelusion aginst ABi Jaf'ar depends on his truth and forenic. And we focus to what include in this correspondence from reasoning that make both of them depend on it to prove his best and truth in succession. So, we depend on it as criterion in the Islamic and political system. And to show that without announce any positive judge to back one the opion of this side or that one in the study of the fourth parts.