Ijma (Consensus) and Qiyas (Analogy)

Beyond the Quran and Sunnah, Islamic legal theory recognizes two additional primary sources: ijma' (scholarly consensus) and qiyas (analogical reasoning). Kamali's treatment of these sources is analytically rigorous, addressing both the theoretical justification for their authority and the practical challenges of establishing and applying them.

Ijma' (consensus) is defined as the agreement of all qualified Muslim scholars (mujtahids) of a particular era on a legal ruling. Its authority rests on the prophetic hadith: 'My ummah will not unite upon an error.' If this is true, then a ruling on which all qualified scholars have agreed must be correct — because agreement of the entire scholarly community of an era on an error is guaranteed not to occur. This gives ijma' a binding authority that, in theory, places it on par with clear Quranic and Sunnah evidence.

However, Kamali carefully examines the practical challenges of ijma'. First, establishing genuine ijma' is historically difficult — determining that all qualified scholars of a given era agreed, without exception, on a given ruling, when scholarship was geographically dispersed and communication limited, is a challenge the classical legal theorists acknowledged. Second, the definition of 'qualified scholar' (mujtahid) involves criteria whose application is itself contested. Third, some classical scholars distinguished between transmitted ijma' (ijma' manqul — explicitly documented historical consensus) and inferred ijma' (ijma' istinbati — consensus inferred from the lack of recorded disagreement), with only the former carrying full legal force.

Qiyas (analogical reasoning) is the extension of a Quranic or Sunnah ruling to a new case on the basis of a shared effective cause ('illah). The standard example is the prohibition of wine — the Quran explicitly prohibits wine (khamr), and the effective cause of the prohibition is its intoxicating property. By qiyas, all intoxicating substances are prohibited, because they share the same effective cause even if not explicitly named in the Quran. Qiyas consists of four elements: the original case (asl) whose ruling is established in the texts; the new case (far') to which the ruling is being extended; the ruling (hukm) of the original case; and the effective cause ('illah) shared by both cases.

The validity of qiyas depends entirely on the correct identification of the effective cause. If the cause is correctly identified as a genuinely defining feature of the original ruling, the extension is valid. If the cause is misidentified or the new case differs from the original in a way that makes the cause inapplicable, the analogy fails. This is why legal reasoning by analogy requires broad knowledge of Islamic law — to correctly identify causes and correctly evaluate differences between cases.