Impact of knowing the cause of delivering precepts on the legal reasoning (Ijtihad)

As cited by some of the Muslim Jurists(Faqih) and Legists (`Usuli), one of the affective elements on the Ijtihad is the knowing the cause of revealing the verses and issuing the narrations. In this article, it has been tried to explain the meaning of knowing the cause of delivering the ordinances, put forward a brief report of its history and necessity, and state and review its related possibilities and viewpoints.The Faqih and `Usuli have divided the phrases, according to their implied meanings, into three categories: obvious, apparent and obscure. In accordance with the writer`s opinion, the mentioned awareness has effected on the apparent and obscure meanings, and provided some evidence in favor of this view point and answered the problems which are raised in this area; but there is no valid evidence that the obvious texts are effected by that awareness, unless it is probable that a text is not clear in an aspect, and the reference to the context of delivering can negate the illusion and claim of clearness of a text.