Ijtihad is an important and old issue in Islam. In the Shia perspective, ijtihad has been popular from the age of the infallibles up until today amongst their companions. Many good changes and improvements have been achieved through this method.
The Noble Prophet (s) sent companions such as Mas’ab bin Umayr and Ma’adh bin Jabal to neighboring areas to propagate the religion and teach its rules.
The Prophet said: “Do not pass a verdict without knowledge or else the angels will curse you.” This shows that the passing of a verdict by a jurist and taqlid was also prevalent in the time of the Prophet (s). Referring to jurists after the Prophet’s death continued until it became much more popular during the lives of Imam Baqir and Imam Sadiq (a). Many jurists were raised during the lives of these two Imams, for example: Abu Basir, Yunis bin Abd al-Rahman, and Aban bin Taghlib.
During the lives of the Imams (a) people would ask the Imams themselves because of easy access and because of the limitation of necessary issues. In reality, the mujtahids would perform taqlid to the Imams, but the Imams would give some the permission of ijtihad and to pass verdicts.
Shia define ijtihad as the ability to derive religious rulings from the clear and apparent meanings of the Quran and Sunnah. This form of ijtihad was popular amongst the companions of the Imams (a) during their lifetimes.
The Noble Prophet (s) sent companions to neighboring areas to propagate the religion and teach its rules, Mas’ab bin Umayr and Ma’adh bin Jabal being clear examples. The Prophet said (s): “Do not pass a verdict without knowledge or else the angels will curse you.” This shows that the passing of a verdict by a jurist and taqlid was also prevalent in the time of the Prophet (s). Referring to jurists after the Prophet’s death continued until it became much more popular during the lives of Imam Baqir and Imam Sadiq (a). Many jurists were raised during the lives of these two Imams. These jurists were sent to various cities to enliven the religion and teach religious rulings. Many people who lived far away and did not have access to the Imams would go to them in order to ask their religious questions and received satisfactory answers from them. This is taqlid and the following are some examples of it:
1. Imam Baqir (a) told Aban bin Taghlib: “Sit in the Mosque of Medina and pass verdicts for the people because I would love to see people like you amongst my Shia.”
2. Ma’adh bin Muslim, a companion of Imam Sadiq (a), went to the central mosque and passed verdicts without the permission of the Imam. When the news reached the Imam he approved of it and encouraged it.
3. Shuayb ‘Aqrquqi said that he told Imam Sadiq (a) that sometimes he wants to ask his religious questions from someone (because he lives far away from the Imam). He then asked the Imam: “Please tell us who we should refer to and whose words should we accept.” The Imam (a): “You may refer to Abu Basir.”
4. Hassna bin Ali bin Yaqtin narrates that he asked Imam Ridha (a): “I am unable to ask you about every religious problem that occurs for me. Is Yunus bin Abd al-Rahman trustworthy; can I take the answers to my religious problems from him?” The Imam (a) replied: “Yes.”
5. Imam Mahdi (a) in his famous letter to Ishaq bin Yaqub, as a general principle, wrote:
“In events that occur refer to those who relate our traditions (jurists) who are my proof (hujjat) over you and I am Allah’s proof over them.”
According to this letter and other traditions, referring to a jurist in the time of the greater occultation took on a new form. The terms ijtihad and taqlid appeared and jurists holding all of the necessary conditions bore the responsibility of passing verdicts and answering religious questions and filled the gap of not being able to have access to the infallible Imam. This has continued on to today and will continue into the future as Shaykh Tusi said: “I have seen the twelver Shia in this way from the time of Imam Ali (a) until today (5th century Hijri) in that they are attached to their jurists regarding religious rulings and worship. They ask the jurists and have received answers when the high jurists show them their verdicts.”
Therefore, the ijtihad that is popular in the Shia seminaries has a long history dating back to the age of the infallible Imams (a). Before this, questions would be asked directly from the infallible Imam (a) who considered it his duty by answering with a general principle and then teaching his companions how to derive specific rulings from this general principle. So, the first mujtahid performed taqlid to the Imam before he reached ijtihad. In the years after this, a number of gifted and educated people answered peoples’ questions by using the words of the Imams. This was the first form of ijtihad which developed and in the time of the occultation the jurists have a large number of traditions and use the principles taught by the Imams (a) in order to realize the answer to a religious problem because all of the issues that are of necessity have been mentioned in traditions. Then, when science evolved and the needs of man increased to such an extent that they were not mentioned in the traditions, jurists used the generalities of the verses and traditions to answer the needs of society. Day by day the society is evolving and ijtihad is spreading out. Today, ijtihad reaches many areas.
For more information one can refer to the dars-e-kharij-e-Usul of Professor Hadavi Tehrani.
 Wasa’il al-Shia, volume 27, chapter 4 and 7
 Historians write that Imam Sadiq (a) had 4000 students who came from around the world to attend his classes. One can refer to Al-Imam al-Sadiq wa al-Madhahib al-Arba’ by Haidar Asad, volume 1, page 69.
 Mustadrak al-Wasa’il, volume 17, chapter 11
 Wasa’il al-Shia, volume 27, page 148
 Wasa’il al-Shia, volume 27, chapter 11, page 142
 Tusi, al-Idah fi Usul al-Fiqh, page 731; Porseshha va Pasokhha Daneshjuyan, pages 42-44
 As an example: Tusi, Istibsar, volume 1, pages 77-78
 The first volume, the Philosophy of the Principles of Jurisprudence, chapter one: the principles of jurisprudence from the beginning to contemporary times, pages 22-38