Extending a Ruling by Its Cause

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.