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. al-kulayni, in rey, and al-sadduq, in qom, were concerned with a traditionalist approach. 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. by developing the theory of the "usul", al-hilli introduced more legal and logical norms which extended the meaning of the "usul" beyond the four principle sources. amili was the first scholar to fully formulate the principles of "ijtihad".