Qiyas: Analogical Reasoning Is a Source of Law

Qiyas takes a ruling already settled by a clear text of the Quran or the Sunna and extends it to a new case that was never explicitly addressed, on the ground that the new case shares the same operative cause, illa, that justified the original ruling. The often cited example is the Quranic prohibition of wine: jurists identify the operative cause as intoxication rather than the specific substance named, and extend the same prohibition by qiyas to any other intoxicant sharing that cause. Ranked as the fourth source of Sunni jurisprudence, after the Quran, the Sunna and ijma, qiyas is what allows a body of revealed text, necessarily finite and addressed to circumstances of its own time, to continue answering genuinely new questions without requiring a jurist to claim personal, unconstrained opinion as a source of law. The four Sunni schools treat qiyas as a disciplined method with identifiable steps, the original case, the new case, the ruling and the shared cause, rather than as a name for informal or intuitive reasoning. Jurists analyse a case of qiyas into four named elements: the asl, the original case already ruled on by revealed text; the far, the new case under consideration; the hukm, the ruling attached to the original case; and the illah, the operative cause shared between the two, which is the element requiring the jurist's own judgment.

The four Sunni schools all recognise qiyas as a legitimate source, but not in equal measure, and the disagreement traces to how confidently a jurist can claim to have identified the true operative cause behind a revealed ruling. The Hanafi school, historically centred in regions with active commercial life and comparatively fewer directly applicable texts, made the widest use of analogical reasoning among the four. The Hanbali school, more cautious about extending rulings beyond what a text explicitly states, applied qiyas more sparingly and only where little alternative existed. Outside the four schools that came to be regarded as the Sunni mainstream, the Zahiri school rejected qiyas altogether, holding that a jurist could never be certain enough of a text's underlying cause to extend it safely, and that law should be derived from the plain, literal sense of revealed text alone. The persistence of that rejected position, even as a minority view, is a reminder that qiyas being one of the four accepted sources was itself a contested outcome rather than an inevitability. Twelver Shia jurisprudence took a different route again: the Jafari school largely declined to adopt qiyas as the Sunni schools define it, relying instead on a narrower role for aql, reason, exercised by a qualified jurist within limits its own legal theory sets out separately.