I just keep keeping on:
Islamic law is seen not as a product of human intelligence, nor as something that can be adapted to changing social needs and ideals. Rather, it is direct from God. In theory, it is immutable. As I have pointed out, there have been various ways in which Muslim jurists have been able to adapt the shariah to changing circumstances. But there is no doubt that this adaptation is quite difficult and can only operate under considerable restriction. Westerners sometimes accuse conservative Muslims of wanting to “turn the clock back.” The charge is often actually true, and many Muslims would cheerfully admit it. They are in fact attempting to go back to the pristine Islam of the seventh century. For Sunnis, it is a return to the days of the “rightly guided caliphs”—Abu Bakr, Umar, Uthman, and Ali—that is wanted. (For the Shiites, it is only Ali who counts.)
There was another potential source of rulings within Islamic law. That principle is known as ijtihad, and means something like “independent reasoning” or “private judgment.” (The word ijtihad comes from an Arabic three-consonant root, jhd, with the basic sense of “striving.” It is closely related to the word jihad, which, as we have seen, is often rendered in English as “holy war.”) Of course, it wasn’t just anybody whose “private judgment” could be validly applied to legal matters. It had to be someone thoroughly versed in the Qur’an, in the body of hadith traditions, and in legal precedent. Qualified judges were to use their own independent reasoning when no clear rule could be found in either the Qur’an or the hadith and when a clear consensus on the question did not exist among their colleagues. Obviously, this allowed for a certain amount of freedom on the part of early Muslim judges. But, gradually, as ijma was reached on more and more issues, the “door of ijtihad” (as Islamic writers call it) was shut.
Today, that door seems firmly closed. Thus, the sources of Islamic shariah law are, beginning at the most authoritative: (1) the Qur’an, (2) accepted hadith reports, (3) reasoning by analogy (qiyas), (4) consensus (ijma), and (5) personal judicial judgment (ijtihad). However, since it is the consensus of the learned community that infallibly separates valid interpretations of the Qur’an and sunna from invalid ones, and that distinguishes analogies that work from those that do not, ijma assumes, in practice, a dominant role in the elaboration of Islamic law.