Shaykh Tusi

Shaykh Tusi (), full name "Abu Jafar Muhammad Ibn Hassan Tusi" (), known as Shaykh al-Taʾifah () was a prominent Persian scholar of the Twelver school of Shia Islam. He became known as the "sheikh of the sect ("shaikh al-ta'ifah")," author of two of the four main Shi'i books of hadith, "Tahdhib al-Ahkam" and "al-Istibsar", and is believed to have founded the Hawza. He also counts as the founder of Shia jurisprudence.
Life.
Shaykh Tusi was born 995 AD/385 AH in Tus in Iran and by 1018 AD/408 AH he was living under the rule of the Buyid dynasty. Shaykh's birth is considered a miracle, as he was born after the twelfth Imam of Shia, al-Mahdi's, supplications. He started his education in Tus (located in Khurasan) where he mastered many of the Islamic sciences of that period. Later, he left Tus to study in Baghdad which was taken by Tughril-bek in 1055 AD/447 AH. There he entered into the circles of Shaykh Al-Mufid as a paramount teacher. It was between the ages of twenty and thirty that he started writing some of his earlier works. By the time he was forty-two, he had learned from Shaykh Murtaza, as well as attended the scholarly circle of Sunni scholars and studied Shafi fiqh. At this time many Muslim scholars in Baghdad, both Sunni and Shiʿite were killed and the house of al-Shaikh al-Tusi burned down, along with his books and the works he had written in Baghdad together with other important libraries of Shi'ite literature. After the fall of Baghdad, Al-Tusi moved to al-Najaf where he died on the 22nd of Muharram in the year 460 AH/2 December 1067.
Influence.
Tusi had an important role in the formation and revival of Shia jurisprudence and law, as his life coincided with the burning of great books and libraries. It is even said that he revived hadith and Islamic jurisprudence. He defended the application of jurisprudence in respect to religious laws. One of his main accomplishments was that he was successful in propagation and making his methodology of argumentation and inference coherent: he had given to Shaykh Mufid a definite formulation of Ijtihad. His dominance was unrivaled for a long time and nearly all Islamic jurisprudence was affected by Shaykh Tusi's opinions. Only three people including Shaykh Tusi are said to have had such an important role in the leadership of Twelver Shia school of law. Some works of Tusi show that he was influenced by precedent jurists like Sallar Deylami. The influence of Shaykh Tusi continued until the emergence of Ibn Idris Hilli, who criticized some of Shaykh Tusi's views. 
Usuli School.
In conflict between two schools of Akhbari and Usuli, Shaykh Tusi defended the Usuli school and claimed that the rival Akhbari were literalists. Shaykh Tusi believed in principles of jurisprudence as the fundamental knowledge in acquiring judgment in Islam. He wrote in the introduction to one of his works as follows:
He also compared the positions of the different legal schools of Islam and showed that there is little difference between them. In cases where differences are present, that they are minor. Shaykh Tusi, like his Masters, refuted the legal analogy ("Qiyyas Fiqhi") in his manual of "Usul Fiqh".
Importance of reason.
His emphasis was on the rational dimension of religion, underlining that principles like the commandment to good and prohibition of evil are indispensable according to reason. Shaykh Tusi also used rational arguments to validate consensus ("ijma") as derived from the principle of "lutf". According to "lutf", God must provide believers with the conditions for religious obedience.
Pioneering.
Tusi was a leading intellectual, producing works of biography ("ilm-rijal)," traditions (hadiths) and compendia of knowledge ("Fihrist"). He also started important developments that allowed Shia clerics to take up some of the roles previously permitted to only imams, such as collecting and distributing religious taxes and organizing Friday prayers.
Najaf Seminary.
According to some scholars, Sheykh Tusi established the Hawzeh of Najaf after migrating from Baghdad.
Works.
He wrote over fifty works in different Islamic branches of knowledge such as philosophy, hadith, theology, biography, historiography, exegesis and tradition. Of the four authoritative sources of the Shiites, two are by Shaykh Tusi, the basic reference books Tahdhib al-Ahkam and Al-Istibsar. Both of these pertain to Hadiths of Islamic jurisprudence. Other books include:
Al-Khilaf.
This book is one of the first in the sphere of comparative jurisprudence written by Tusi. He tries to collect all opinions of law schools of Islam in this book. The book also shows that there is great accordance between Shia school of law and other schools; the differences exist merely in minor problems, such as "furu". This book collected opinions unique to Shia, and also conflicting Sunni opinions in detail.