In order to protect the Shariah from the danger of innovation and distortion, the great scholars of usul laid down rigorous conditions which must be fulfilled by anyone wishing to claim the right of ijtihad for himself. These conditions include:
(a) mastery of the Arabic language, to minimise the possibility of misinterpreting Revelation on purely linguistic grounds;
(b) a profound knowledge of the Quran and Sunnah and the circumstances surrounding the revelation of each verse and hadith, together with a full knowledge of the Quranic and hadith commentaries, and a control of all the interpretative techniques discussed above;
(c) knowledge of the specialised disciplines of hadith, such as the assessment of narrators and of the matn [text];
(d) knowledge of the views of the Companions, Followers and the great imams, and of the positions and reasoning expounded in the textbooks of fiqh, combined with the knowledge of cases where a consensus (ijma) has been reached;
(e) knowledge of the science of juridical analogy (qiyas), its types and conditions;
(f) knowledge of ones own society and of public interest (maslahah);
(g) knowing the general objectives (maqasid) of the Shariah;
(h) a high degree of intelligence and personal piety, combined with the Islamic virtues of compassion, courtesy, and modesty.
A scholar who has fulfilled these conditions can be considered a mujtahid fil-shar, and is not obliged, or even permitted, to follow an existing authoritative madhhab
. This is what some of the Imams were saying when they forbade their great disciples from imitating them uncritically. But for the much greater number of scholars whose expertise has not reached such dizzying heights, it may be possible to become a mujtahid fi’l-madhhab, that is, a scholar who remains broadly convinced of the doctrines of his school, but is qualified to differ from received opinion within it. There have been a number of examples of such men, for instance Imam al-Nawawi among the Shafi'is, Qadi Ibn Abd al-Barr among the Malikis, Ibn Abidin among the Hanafis, and Ibn Qudama among the Hanbalis. All of these scholars considered themselves followers of the fundamental interpretative principles of their own madhhabs, but are on record as having exercised their own gifts of scholarship and judgement in reaching many new verdicts within them. It is to these experts that the Mujtahid Imams directed their advice concerning ijtihad, such as Imam al-Shafi'i's instruction that ‘if you find a hadith that contradicts my verdict, then follow the hadith’. It is obvious that whatever some writers nowadays like to believe, such counsels were never intended for use by the Islamically-uneducated masses. Imam al-Shafi`i was not addressing a crowd of butchers, nightwatchman and donkey-drovers.