Ijtihad means jurisprudent's opinion about reasons and purposes of Shari'ah to gain conjecture about juridical sentence of the subjects which have not explained their sentences. This historical duty has been acquitted in different manners in different segments of history. Before appearance of Islamic religions Free and Individual Ijtihad and then after appearance of Islamic religions Interior Ijtihad have been usual. Interior Mojtahids have been categorized in Montasab, Ahle Takhrij and Ahle Tarjih, and they were like head of the religions. Yet they were followers of them because of the strength of their sources and certainty of their standards and norms. Passage from free ijtihad to interior ijtihad has not disconnected the process of ijtihad, so subjects like imitation of one mojtahid from another and stoppage of ijtihad have not appeared.
)