Among the four foundational sources of Islamic law — the Qur'an, the Sunnah, ijma (consensus), and qiyas (analogical reasoning) — none has generated as sustained or as consequential a theoretical literature as ijma. From its earliest usage in the integrative politics of the first Islamic century to its elaborate systematisation by the classical jurists of the fourth and fifth centuries of the Hijrah, and from there to the reformist controversies of the modern era, ijma has served simultaneously as a principle of legal authority, a mechanism of community integration, and a contested site of theological argument. Ahmad Hasan's The Doctrine of Ijma in Islam is the definitive English-language study of this doctrine in its full historical and theoretical scope.
Hasan opens with an account of ijma as a socio-political and theological phenomenon before it became a formal legal doctrine. Drawing on an extensive range of primary sources, he traces the emergence of the concept of jama'ah — the integrated community — in the period of crisis following the Prophet's death, showing how the competing appellations of the early Muslim factions (Ahl al-Sunnah wal-Jama'ah, Ahl al-Hadith, Ahl al-Ijma) reflect the gradual crystallization of consensus as a marker of Sunni orthodoxy. The analysis of the hadith literature on ijma — including the celebrated tradition 'my community will not agree on an error' — is particularly careful, distinguishing between the tradition's original integrative function and its later deployment as a technical juridical argument for the infallibility of scholarly consensus.
The political dimension of ijma receives extended treatment across two chapters. Hasan examines the role of ijma in the legitimation of the early caliphate — the election of Abu Bakr, the functions of the shura council, and the gradual separation of religious and political authority under the Umayyads and Abbasids — and situates the classical definition of ijma as the 'agreement of the scholars' within the rise of the ulama as a social class wielding authority independent of the political caliphate. The discussion of sovereignty, legislation, and the nature of Islamic law's claim to divine sanction engages with both classical theorists (al-Mawardi, Fakhr al-Din al-Razi) and modern political theorists (Ernest Barker), making it valuable for students of Islamic political philosophy as well as legal history.
The theoretical core of the study comprises nine chapters devoted to the classical doctrine in its developed form. Hasan examines the Qur'anic and hadith-based arguments for ijma's authority (Chapter III), reconstructing and evaluating the debates between the doctrine's defenders (al-Jassas, al-Ghazali, al-Amidi, al-Razi, al-Juwayni) and its opponents (al-Nazzam, Ibn Hazm, al-Shawkani), including their sustained engagement over the meaning of Qur'anic verses 2:143, 4:115, 3:110, and 4:59. He then moves through the classical definition and its component parts (Chapter IV); the qualifications for competence — the mujtahid, the masses, the morally corrupt scholar, and the heretic (Chapter V); the contested question of which generation's consensus carries binding authority (Chapter VI); the categories of subject matter falling within ijma's jurisdiction (Chapter VII); and the validity of tacit consensus — ijma sukuti — including its rejection by al-Shafi'i and al-Ghazali and its defence by the Hanafi jurists (Chapter VIII).
The treatment of the value and abrogation of ijma (Chapter XI) and the diversity of opinion within the theory itself (Chapter XII) demonstrates Hasan's command of the full range of the juridical literature — Hanafi, Maliki, Shafi'i, and Hanbali — and his ability to identify the underlying structural tensions that prevented the classical theory from achieving the coherence its proponents sought. The analysis of Ibn Hazm's and Ibn Taymiyah's restrictive positions, and of the Shi'i theory of infallibility, further extends the comparative reach of the study.
Chapter XIII — A Comparative Study of Ijma: Sangha, Sanhedrin, and Church — is one of the most original contributions of the work. Tracing the origins, development, and functions of analogous institutions of collective religious authority in Buddhism, Judaism, and Christianity, Hasan identifies both the universal dimension of such institutions (every mature religion requires a mechanism for conserving and directing its tradition) and the distinctive features of ijma (its absence of hierarchy, its informality, its reliance on tacit accumulation of scholarly opinion). The discussion draws on sources ranging from the Mishnayoth and the Jewish Encyclopaedia to the acts of the ecumenical councils and the ecclesiology of Orthodox Christianity, and it engages with the observations of H.A.R. Gibb on the analogy between ijma and the Church councils.
The final chapter surveys the major modern reinterpretations of ijma across two centuries of Islamic reform thought. Shah Wali Allah's insistence that genuine ijma requires the enforcement of the caliph and the consensus of the scholarly community — and his restriction of practical ijma to the age of the first three Caliphs — is presented as a liberal orthodox position that differs structurally from the classical definition while remaining committed to its spirit. Sayyid Ahmad Khan's validation of ijma only when supported by Qur'anic or hadith evidence, Ubayd Allah Sindhi's sharp distinction between Sunnah and ijma, and Muhammad Iqbal's proposal to transfer the power of ijtihad to a Muslim legislative assembly are each examined in their intellectual context and assessed critically. Mufti Muhammad Abduh's reinterpretation of ijma as the consensus of Auli al-Amr (men of authority) in the broader social sense, and Ziya Gokalp's sociologically inflected distinction between the dogmatic and social dimensions of the Shari'ah, complete the survey. The chapter concludes with Gibb's influential characterization of ijma as the 'conscience of the community' and 'vox populi' — a slowly accumulating general will rather than a formal decision of a defined body.
The Doctrine of Ijma in Islam is an essential acquisition for academic libraries with collections in Islamic studies, Islamic law, comparative religion, and the history of political thought. It is the standard reference work on its subject and has not been superseded.