usuls

Usul, from the Arabic word meaning roots or principles, in Islamic usage most often refers to Usul al-Fiqh, the science of the principles and methods used to derive Islamic legal rulings. The term also appears in broader discussions of foundational ideas in theology and law, but in jurisprudence it denotes the theory of sources, evidence, and reasoning that underpins fiqh, the body of Islamic law. Usul al-Fiqh aims to identify what counts as a valid proof, how to interpret sources, and how to apply rules to new situations, while outlining the limits of legal reasoning.

Historically, Usul al-Fiqh began to take shape in the early medieval period and was systematized by scholars across the major Sunni schools. Key figures contributed to formalizing how rulings are derived from primary sources and rational argument. While all four major Sunni madhhabs (Hanafi, Maliki, Shafi'i, Hanbali) emphasize Quran and Sunnah as foundational, they differ in auxiliary methods and criteria. In Shia Islam, Usul al-Fiqh likewise centers on sources such as the Qur'an and Sunnah but incorporates distinct approaches to authority and interpretation. Across traditions, discussions of ijma (consensus), qiyas (analogy), and various juridical maxims and methods—such as maslahah (public interest), urf (custom), and istihsan (juristic preference)—illustrate the range of tools scholars use to derive rulings.

Core sources and methods typically include: the Qur'an and the Sunnah as primary proofs; ijma and qiyas as principal theoretical instruments; and additional tools like urf, maslahah mursalah, sadd al-dhara'i, and reason (aql) to varying degrees depending on the school. Usul al-Fiqh also addresses the reliability and interpretation of evidence and the conditions under which independent legal reasoning (ijtihad) is required or constrained.

Today, Usul al-Fiqh remains central to Islamic legal theory, guiding interpretation of modern issues and shaping debates about authority, methodology, and the limits of human reason in law.