IJMĀʿ . The Arabic term ijmaʿ, which means "agreement" or "consensus," becomes in Islamic jurisprudence the designation for one of the four sources of law posited by classical Sunnī theory, namely the consensus of the Muslim community. This consensus ranks as the third of the four sources, the first, second, and fourth of which are the Qurʾān, the sunnah (custom) of the prophet Muḥammad, and analogical reasoning (qiyā s). For the majority of Sunnī legal theorists, the work of constructing legal rules is carried on by qualified scholars, called mujtahid s, on behalf of the community as a whole. Whatever these scholars agree upon is therefore constitutive of the consensus of the community, and it is not necessary for them to take into account the views of an unqualified laity. The majority of theorists further hold that an authoritative consensus is fully constituted at the very moment when the community's living scholars agree unanimously on a rule of law; it is not necessary to allow additional time for individual scholars to reconsider their decisions or to wait until the entire body of scholars involved in the consensus has passed away, thus eliminating any possibility of reconsideration. Once constituted, a consensus is irrevocable. It represents, in the view of all Sunnīs, an infallible and immutable statement of the divine law, or sharīʿah. As such, it is worthy to be made the basis of further legal constructions by individual scholars through either interpretation or analogical deduction. It is for this reason that ijmāʿ is included among the sources of law.
Sunnī theorists agree that the authority of consensus must rest upon revealed declaration and that all attempts to base that authority upon purely rational considerations are futile. The only self-constituted authority is that of the Creator-Lord; the authority of consensus can be nothing more than its derivative. However, the search for a clear-cut divine endorsement for the authority of consensus has been one of the most arduous tasks undertaken by classical Islamic jurisprudence. The various loci classici employed in this search have all proved to be in some degree problematic: The relevant Qurʾanic passages allow diverse interpretations, and the relevant dicta of the Prophet (as recorded in ḥadīth, the literary embodiment of the sunnah ) are not only open to differing interpretation (despite their being in some cases more precise than the Qurʾān in their support of the authority of consensus, as in the case of the well-known dictum, "My community will never agree upon an error") but are also fraught with text-critical uncertainties. Scholarly opinion has therefore been divided as to whether or not the textual evidence for the authority of consensus is entirely conclusive. Among those who acknowledge that it is not, compensation for the resulting element of uncertainty is found in the principle that on issues relating to human conduct, an authority need not be conclusively grounded in the texts in order to acquire validity, so long as there is sufficient textual evidence to make the legitimacy of that authority more likely than its nonlegitimacy. In this view, the case for the authority of consensus thus rests upon the principle of the sufficiency of probable textual evidence.
While a few Sunnī theorists have conceded to the consensus the privilege of engendering rules that have no demonstrable textual basis, the great majority have restricted its role to granting finality to rules constructed on the basis of the texts. Accordingly, the consensus must emerge from the exegetical deliberations of individual scholars. Individuals qua individuals can at best, according to the general view, produce only probable constructions of the law; their exegesis can never be more than tentative. This exegesis is in fact called ijtihād ("exertion," whence the term mujtahid) precisely because of its tentative character. The exegetes, as fallible mediators of the divine law, exert themselves in the effort to achieve, through philological procedures and analogical reasoning, the most accurate construction of that law possible for them. When the results of their efforts are confirmed by the consensus of their contemporaries, then, and only then, do these results acquire the stature of an infallible and immutable pronouncement. This confirmation may take the form of either explicit espousal or silent consent. The theorists differ, however, as to the value of the latter. The confirmation must, furthermore, be unanimous; a consensus cannot be constituted by a mere majority.
Because the Islamic tradition does not provide for the public certification or official convening of legal scholars and because unanimity on a scale vast enough to embrace the entire Muslim world would be difficult to achieve in the best of circumstances, the consensus, as conceived in the classical theory, has been virtually unrealizable throughout the greater part of Islamic history. While few theorists have accepted the view of Dāʾūd al-Ẓāhirī (d. ah 270/884 ce) and his followers, which restricted the prerogative of consensus making to the first generation of Muslims who were still alive after the Prophet's death, it is not surprising that the classical theorists have generally drawn their examples of consensus from that generation. In so doing, they have implied that only in the earliest period of Islam, when those Muslims who had been in sufficient contact with the Prophet to be deemed authorities ("Companions of the Prophet") were still concentrated in one locality, did the circumstances required for the constitution of a true consensus exist and that thereafter the consensus has remained more a theoretical possibility than a historical actuality. The notion that the consensus is identifiable with Muslim public opinion is distinctly modern.
In Shīʿī theory, consensus is reckoned among the sources of law, but it cannot, according to that theory, be regarded as properly constituted unless the divinely appointed leader, the imam, is present within the community. Because the word of the imam is considered infallible apart from the consensus, the consensus is deprived of the role it occupies in Sunnī theory as the infallible finalizer of rules of law and becomes, in effect, the community's affirmation of solidarity with the imam, such that its teaching and his are one and the same. Thus, from the Shīʿī point of view, the consensus may be deemed a source of law only by special license, and this status is granted only insofar as the consensus is presumed identical with the doctrine of the imam.
There is as yet no monograph in a Western language devoted specifically to ijmaʿ. For a more extensive survey of the subject than the above, see the article "Idjmāʿ" by Marie Bernand in The Encyclopaedia of Islam, new ed. (Leiden, 1960–). On the controversies over the authority of consensus, see George F. Hourani's "The Basis of Authority of Consensus in Sunnite Islam," Studia Islamica 21 (1964): 13–60. The standard Islamicist view of ijmaʿ and its historical development can be found within the pages of Joseph Schacht's An Introduction to Islamic Law (Oxford, 1964). For a French translation of the writing of an important classical author, Abuʾl Ḥusayn al-Baṣrī, on ijmaʿ, see Marie Bernand's L'accord unanime de la communauté comme fondement des statuts légaux de l'Islam (Paris, 1970).
Bernard G. Weiss (1987)