Sunni Islam recognizes four sources from and through which the laws governing its conduct are derived. These are the Qur'an, the Sunna of the Prophet, the consensus (ljmā') of the community and its scholars, and qiyās, the juridicological method of inference. The first two sources provide the jurist with the material from which he is to extract through qiyas and ijtihād (the disciplined exercise of mental faculty) the law which he believes to the best of his knowledge to be that decreed by God. Except for a relatively limited number of cases where the Qu'an and the Sunna offer already-formulated legal judgments, the great majority of furū' cases, which constitute the body of positive and substantive law, are derived by qiyas. Thus, qiyas may be used to “discover” the judgment of a new case provided that this case has not already been solved in the two primary sources. The process of legal reasoning which qiyas involves is charged with innumerable difficulties not the least of which is finding the circle of common similarity, the 'illa, between the original case in the texts and the new case which requires a legal judgment. Since finding the 'illa entails a certain amount of guesswork (zann) on the part of the jurist and since it is highly probable that the 'illa is extracted from a text which is not entirely reliable or a text capable of more than one interpretation, Sunni jurists deemed the results of qiyas to be probable (zannī). It is only at this point that consensus may enter into play in the legal process. Should Muslims, represented by their jurists, reach an agreement on the validity of a zanni legal judgment, such judgment is automatically transferred from the domain of juristic speculation to that of certainty (qat', yaqīn). Consensus then renders this judgment irrevocable, not to be challenged or reinterpreted by later generations. Furthermore, this judgment, being so irrevocable, acquires a validity tantamount to that of the Qur'an and the highly reliable traditions embodied in the Sunna of the Prophet. Thus, such a case with its established judgment becomes a precedent according to which another new legal question may be solved. It is only in this sense that consensus functions as a source of law, a source which is infallible.
Extensive Analysis on Generation and Consensus Mechanisms of Clustering Ensemble: A Survey
