Qiyās
from 800 Systematised by al-Shāfiʿī around 820
Extend an existing ruling to a new case, but only when you can name the operative reason behind the original and show it is present in the new one.
- Active
- from 800
- Where
- Baghdad and Cairo
- Also
- qiyās
- Status
- In use
- Tradition
- Non-Western procedures
What it is
Qiyās extends a settled ruling to an unsettled case. It has four named parts: the original case, the new case, the ruling, and the ʿilla — the operative cause, the feature of the original case that the ruling actually turns on.
The ʿilla is what raises it above loose analogy. Two cases may resemble each other in a dozen respects, and the extension is valid only if they share the one respect that the ruling was responding to. Identifying that feature is the whole discipline, and Islamic jurisprudence developed elaborate procedures for it.
How it works
Identify the original case and its settled ruling. Determine the ʿilla — the feature the ruling responds to, not merely a feature present. Test the candidate: does the ruling track it across other cases, and does its absence remove the ruling? Establish that the ʿilla is present in the new case. Extend the ruling.
The third step is what most attempted analogies fail. A feature that merely accompanies the ruling is not the ʿilla, and the test is whether the ruling varies with it.
The form of the inference
- The original case carries a settled ruling
- The ruling turns on a specific operative feature, the ʿilla
- The ʿilla is present in the new case
- No counter-indication distinguishes the two cases
- Therefore the ruling extends to the new case
The argument
Proposition The confined-space procedure applies to the new grain silo.
- The original case: the effluent pit, which the procedure names expressly and for which entry requires a permit, atmospheric testing and a standby person.
- Determining the operative feature: the procedure's own hazard statement gives it as an atmosphere that can become oxygen-deficient or toxic without warning in a space that cannot be exited quickly.
- Testing the candidate: the procedure applies to the pit, the digester and the sealed tanker, all of which have that feature, and does not apply to the open sump, which has restricted access but no atmospheric hazard. So the ruling tracks the atmosphere, not the access.
- The new case: the grain silo. Grain in storage consumes oxygen and can produce carbon dioxide at depth; entry is by a top hatch with a fixed ladder and no quick exit.
- No counter-indication: nothing distinguishes the silo in a way relevant to the operative feature. That it holds a food product rather than waste is a difference the ruling has never tracked.
Therefore The confined-space procedure extends to the silo, and the extension rests on the atmospheric hazard rather than on any resemblance between grain and effluent.
The open sump is what makes this rigorous. It resembles the pit in the obvious way — restricted access — and is excluded, which is how the operative feature was identified rather than guessed.
What it is good for
Applying any rule to a case its drafters did not anticipate. It is the most disciplined form of analogical reasoning anyone has produced, and its insistence on naming the operative reason is directly transferable to safety procedure, policy and contract.
Where it fails
The ʿilla can be constructed to reach a desired result. Since the jurist selects which feature the ruling turns on, and a ruling is usually consistent with several candidate features, the method can be steered — and the tradition's enormous literature on identifying the ʿilla exists precisely because this was recognised as the central danger.
It was also rejected outright by some. The Ẓāhirī school held that a ruling applies where it applies and nowhere else, on the ground that extending it substitutes human reasoning for the text. That position lost, and it was not obviously wrong.
Common misconceptions
That it is the same as reasoning from precedent in the common law. It is close, and the difference matters: common law precedent binds through the reasoning of a prior court, while qiyās extends a ruling through a feature of the world that the ruling responds to.
Where it came from
Systematised by al-Shāfiʿī around 820 as one of the four sources of law, alongside the Qurʾān, the sunna and consensus.
What became of it
Accepted by three of the four Sunni schools, restricted by some and rejected by the Ẓāhirīs, and still the mechanism by which classical rulings reach modern cases.
Lasting influence
It is how Islamic law addresses questions its sources never contemplated, from banking instruments to medical technology.
Why it still matters
In daily use across a legal tradition serving a substantial share of the world.
Put another way
Not two things that look alike, but two things with the same thing wrong with them.
Texts
Al-Shāfiʿī, Al-Risāla
The founding work of Islamic legal theory, and where qiyās is established as a source with conditions attached.
Where to start
Take a rule you apply at work and name what it actually turns on. Then find the case that resembles it and is excluded. That case is how you check.
The surprising bit
Two legal traditions with no contact — the common law and Islamic jurisprudence — built their entire capacity to handle new cases on the same inference, and both spent centuries arguing about how to identify what a rule really turns on.
In their own words
On everything that befalls a Muslim there is a binding ruling, or an indication of the way to the right answer
Who held it
the Ẓāhirī school
Connections
- Relies on
- Argument by analogy
- Influenced
- Ijtihād
- Parallel to
- Argument by analogy
The verdict
The most rigorous account of analogical extension anywhere, and steerable by whoever names the operative cause.