Ya`qub b.

Ya`qub b. Ishaq al­Razi al-Kulayni (d. 328/939). It contains over 16,000 traditions from the Prophet and the Imams covering all aspects of the usul (the 'roots', mainly theological) and the furu` (the 'branches', mainly preceptual) of the religion. The khabar al­wahid is that kind of tradition which has not reached the status of tawatur, i.e., has not been narrated by so many traditionalists that there is no doubt about its validity.

Under certain conditions, such traditions are admissible as proof (hujja) in the derivation of precepts. Abu Ja`far Muhammad b. al­Hasan b. `Ali al­Tusi (385/995 ­ 460/1067), the Shaykh al­Ta'ifa (the Chief [scholar] of the [Shi`a] Sect), author of ''`Uddat al­Usul" (Tehran, 1314). Jamal al­Din Abu `Amr `Uthman b. `Umar b. Abi Bakr b.

Yusuf, Ibn al­Hajib (570/1174 ­646/1249), the Maliki legist, author of "Muntaha al­Su'al wa l­Amal fi `ilmay al­Usul wa l­Jada"' which he condensed into his "Mukhtasar al­Usul". Besides al­Iji's commentary on this abridgement, there is also one by the `Allama al­Hilli (see below, note 19), called "Ghayat al­Usul" which he wrote to refute al­Iji's (see: ''al­Dhari`a'', XIV, p.56). Abu Hamid Muhammad al­Tusi al­Ghazali (450/1058 ­ 505/1 111), who followed the Shafi`i madhhab.

The full title of his work on jurisprudence is "al­Mustasfa min `ilm al­Usul" (2 vols, Cairo, 1356). The main substantial difference between Shi`i and Sunni ijma` is that the former must contain the opinion of the Imam in the consensus. The discussion of how this can be achieved during the Imam's occultation forms one of the important parts of the science of usul. Jamal al­Din Abu Mansur, Hasan b. Yusuf b. `Ali b.

Mutahhar, the `Allama al­Hilli (648/1250 ­ 726/1325), the famous legist, philosopher and mutakallim, author of "Tahdhib Tariq al­ Wusul ila `ilm al­Usul'' (Tehran, 1308). Abu Ja`far, Muhammad b. `Ali b. al­Husayn b. Babawayh al­Qummi (d. 381/991). These are: "al­Kafi" (see note 13); "Man la Yahdurahu l­Faqih " (ed. H. M. Khirsan, 4 vols, Najaf, 1957, by 1958­62), also by al­Tusi. The fourteen "impeccables": i.e., the Prophet, his daughter Fatimat al­Zahra, and the twelve Imams.

After the student of fiqh has mastered the necessary sciences, he may, if his teacher considers him to be capable of deriving his own legal opinions, receive a certificate authorizing him to do so; but he still cannot be followed by others in taqlid.