Usulism (Arabic: الأصولية, romanized: al-ʾUṣūliyya) is the majority school of Twelver Shia Islam in opposition to the minority Akhbarism.
The Usulis favor the use of ijtihad (reasoning) in the creation of new rules of jurisprudence; in assessing hadith to exclude traditions they believe unreliable; and in considering it obligatory to obey a mujtahid when seeking to determine Islamically correct behavior.
In addition to assessing the reliability of the Hadith, Usuli believes the task of the legal scholar is to establish intellectual principles of general application (Usul al-fiqh), from which particular rules may be derived by way of deduction.
"[4] By their debates and books, Al-Mufid, Sayyid-al Murtada, and Shaykh al-Tusi in Iraq were the first to introduce the Uṣūl al-fiqh (principles of Islamic jurisprudence) under the influence of the Shafe'i and Mu'tazili doctrines.
The second wave of the Usuli was shaped in the Mongol period when al-Hilli introduced the term mujtahid, meaning an individual qualified to deduce ordinances on the basis of authentic religious arguments.