Principles of Islamic jurisprudence

Principles of Islamic jurisprudence (Arabic: أصول الفقه, romanized: ʾUṣūl al-Fiqh) are traditional methodological principles used in Islamic jurisprudence (fiqh) for deriving the rulings of Islamic law (sharia).

Traditional theory of Islamic jurisprudence elaborates how the scriptures (Quran and hadith) 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 hadith, the classical theory of Sunni jurisprudence recognizes secondary sources of law: juristic consensus (ijmaʿ) and analogical reasoning (qiyas). It 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 (madhahib). 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 Twelver Shia jurisprudence parallels that of Sunni schools with some differences, such as recognition of reason (ʿaql) as a source of law in place of qiyās and extension of the notions of hadith and sunnah to include traditions of the imams.

Uṣūl al-fiqh is a genitive construction with two Arabic terms, uṣūl and fiqh. Uṣūl means roots or basis. Some says, Uṣūl, the plural form of Aṣl, means Rājih (preponderant). It also signifies Qā’idah (rules), which is the real-world application of the word. For example: "every sentence must contain a verb" is a rule of Grammar. Fiqh linguistically refers to knowledge, deep understanding or comprehension. In the context of Islamic law, it refers to traditional Islamic jurisprudence.^{[citation needed]}

Classical jurists held that human reason is a gift from God which should be exercised to its fullest capacity. However, they believed that use of reason alone is insufficient to distinguish right from wrong, and that rational argumentation must draw its content from the body of transcendental knowledge revealed in the Quran and through the sunnah of Muhammad.

In Islam, the Quran is considered to be the most sacred source of law. Classical jurists held its textual integrity to be beyond doubt on account of it having been handed down by many people in each generation, which is known as "recurrence" or "concurrent transmission" (tawātur). Only several hundred verses of the Quran have direct legal relevance, and they are concentrated in a few specific areas such as inheritance, though other passages have been used as a source for general principles whose legal ramifications were elaborated by other means.

The body of hadith provides more detailed and practical legal guidance, but it was recognized early on that not all of them were authentic. Early Islamic scholars developed a methodology for evaluating their authenticity by assessing trustworthiness of the individuals listed in their transmission chains. These criteria narrowed down the vast corpus of prophetic traditions to several thousand "sound" hadiths, which were collected in several canonical compilations. The hadiths which enjoyed concurrent transmission were deemed unquestionably authentic; however, the vast majority of hadiths were handed down by only one or a few transmitters and were therefore seen to yield only probable knowledge. The uncertainty was further compounded by ambiguity of the language contained in some hadiths and Quranic passages. Disagreements on the relative merits and interpretation of the textual sources allowed legal scholars considerable leeway in formulating alternative rulings.

Consensus (ijma) could in principle elevate a ruling based on probable evidence to absolute certainty. This classical doctrine drew its authority from a series of hadiths stating that the Islamic community could never agree on an error. This form of consensus was technically defined as agreement of all competent jurists in any particular generation, acting as representatives of the community. However, the practical difficulty of obtaining and ascertaining such an agreement meant that it had little impact on legal development. A more pragmatic form of consensus, which could be determined by consulting works of prominent jurists, was used to confirm a ruling so that it could not be reopened for further discussion. The cases for which there was a consensus account for less than 1 percent of the body of classical jurisprudence.

Analogical reasoning (qiyas) is used to derive a ruling for a situation not addressed in the scripture by analogy with a scripturally-based rule. In a classic example, the Quranic prohibition of drinking wine is extended to all intoxicating substances, on the basis of the "cause" (ʿilla) shared by these situations, which in this case is identified to be intoxication. Since the cause of a rule may not be apparent, its selection commonly occasioned controversy and extensive debate. Twelver Shia jurisprudence does not recognize the use of qiyās, but relies on reason (ʿaql) in its place.