The Operative Cause and Why the Schools Bound Analogy Differently

Al-Shafii's achievement was not inventing analogy, jurists had reasoned from precedent before him, but closing the list of sources at four and making analogy the last and most disciplined of them, subordinate to text and consensus rather than a free standing method a judge could reach for whenever a text ran short. His Risala set out the operative cause, the illa, as the hinge the whole method turns on: a jurist does not simply notice that two cases resemble each other, he must identify the specific legal reason behind the original ruling and show that reason present in the new case, so that reasoning by resemblance is anchored to the law's own stated rationale rather than to human intuition about likeness.

The later schools built precise systems around finding that reason. Hanafi jurisprudence developed the companion method of istihsan, a preference the jurist can invoke to depart from a strict analogy when a stronger, if less obvious, textual or equitable ground supports it, a move Shafii jurists have long criticized as smuggling personal judgment back into a method built to exclude it. The Zahiri school went further still, rejecting analogy entirely on the ground that God's law is either stated or silent, and a jurist who extends it by inference is legislating rather than interpreting.