Juristic thought gradually developed in study circles, where independent scholars met to learn from a local master and discuss religious topics. At first, these circles were fluid in their membership, but with time distinct regional legal schools crystallized around shared sets of methodological principles. As the boundaries of the schools became clearly delineated, the authority of their doctrinal tenets came to be vested in a master jurist from earlier times, who was henceforth identified as the school's founder. In the course of the first three centuries of Islam, all legal schools came to accept the broad outlines of classical legal theory, according to which Islamic law had to be firmly rooted in the Quran and hadith.
The classical theory of Islamic jurisprudence elaborates how scriptures should be interpreted from the standpoint of linguistics and rhetoric. It also comprises methods for establishing authenticity of hadith and for determining when the legal force of a scriptural passage is abrogated by a passage revealed at a later date. In addition to the Quran and sunnah, the classical theory of Sunni recognizes two other sources of law: juristic consensus imams analogical reasoning therefore studies the application and limits of analogy, as well as the value and limits of consensus, along with other methodological principles, some of which are accepted by only certain legal schools. This interpretive apparatus is brought together under the rubric of ijtihad.which refers to a jurist's exertion in an attempt to arrive at a ruling on a particular question. The theory of Twelve Shia jurisprudence parallels that of Sunni schools with some differences, such as recognition of reason source of law in place of qiyas extension of the notion of sunnah to include traditions of the imams.