Usul is plural of definition
Usul is plural of . Asl which literally means ‘proof’, ‘root’, ‘origin’ and ‘source’. Here the word ‘usul denote rules or principles on which a branch of knowledge may be founded and thus ‘usul al-fiqh’ has been translated in this work as the ‘principles of Islamic jurisprudence’. However, some writers have described it as ‘the science of the sources and methodology of the law’ which is correct though but seems to be incomplete. So far the definition of Usul al-Fiqh is concerned it has been defined by some scholars as “the aggregate, considered per se, of legal proofs and evidence that, when studied properly, will lead either to certain knowledge of a Shari`ah ruling or to at least a reasonable assumption concerning the same; the manner by which such proofs are adduced, and the status of the adducer”. See Fakhr Al-Din Al-Razi, Al Mahsul Fi `Ilm Usul al-Fiqh. 1979. Taha Jabir Al-`Alwani (ed.), Riyadh: Imam Muhammad Ibn Sa`ud Islamic University, 1st ed., vol.1.p.94.