Consensus, analogical reasoning, and the scholarly effort to reach a ruling — the basic tools of Islamic legal methodology.
Classical usul al-fiqh (the methodology of Islamic law) recognises the Qur’an and the Sunnah as the two primary textual sources, and adds two further tools the majority of scholars use to reach rulings on matters those texts do not address directly: ijma’ (consensus) and qiyas (analogical reasoning).
Ijma’ refers to the agreement of qualified scholars on a ruling, most authoritatively understood as the consensus of the Companions or of the qualified scholars of a given generation. Once genuine ijma’ is established on a matter, it is treated as binding — though establishing that a true, complete consensus actually exists on a specific point is itself something scholars can disagree about. Qiyas is the process of extending a known ruling to a new case that is not directly addressed in the texts, on the basis of a shared underlying reason (’illah). A commonly cited example is extending the Qur’anic prohibition of khamr (wine) to other intoxicating substances, on the shared reason that both intoxicate the mind.
Ijtihad is the disciplined effort of a qualified scholar (a mujtahid) to derive a ruling from these sources where the answer is not already settled by clear text or established consensus. It requires deep knowledge of Arabic, the Qur’an and Sunnah, the established rulings of earlier scholars, and the methodology of the school being applied. This is distinct from taqlid — following the ruling of a qualified authority — which has been the practical norm for the great majority of Muslims, including most scholars outside their own area of specialism (see the previous lesson).
Not every scholar or school has weighted these four sources identically. The Zahiri school, historically associated with Dawud al-Zahiri and later Ibn Hazm, is well known for limiting or rejecting qiyas as a source, preferring to rely more strictly on the apparent (zahir) wording of the Qur’an and Sunnah. HikmahBridge notes this for completeness rather than treating it as a live option most readers need to weigh — the Zahiri school is not among the four schools most Muslims follow today.
Key points
- Alongside the Qur'an and Sunnah, most scholars recognise ijma' (scholarly consensus) and qiyas (analogical reasoning) as sources for deriving rulings.
- Qiyas extends a known ruling to a new case based on a shared underlying reason ('illah), such as extending the prohibition of wine to other intoxicants.
- Ijtihad is the disciplined effort of a qualified scholar to derive a ruling where the answer isn't already settled; taqlid — following a qualified authority — is the historical norm for non-specialists.
- Not all scholars weight these sources identically — the Zahiri school, for example, is known for limiting or rejecting qiyas.
Scholarly notes
This is a simplified overview of a technical field (usul al-fiqh) that classical scholarship treats in far greater depth, including many sources and sub-categories beyond the four named here. It is intended to give a general sense of the methodology, not to equip a reader to perform ijtihad.
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