Istislah (Arabic استصلاح "to deem proper") is a method employed by Muslim jurists to solve problems that find no clear answer in sacred religious texts. It is related to the term مصلحة Maslaha, or "public interest" (both words being derived from the same triconsonantal root, "ṣ-l-ḥ"). Extratextual pragmatic considerations are commonly accepted in islamic jurisprudence concerning areas where the Quran and the practices of the earliest Muslim generations provide no specific guidance. However, appeals to istislah or maslaha are controversial when the goal is reforming what has been considered to be divinely revealed law.
Istislah bears some similarities to the natural law tradition in the West, as exemplified by Thomas Aquinas. However, whereas natural law deems good that which is known self-evidently to be good, according as it tends towards the fulfilment of the person, istislah calls good whatever is connected to one of five "basic goods". Al-Ghazali abstracted these "basic goods" from the five legal precepts in the Quran and Sunnah—religion, life, reason, lineage (or offspring), and property. In this classical formulation, istislah differs from utilitarianism—"the greatest happiness for the greatest number of people"—because something that results in "the greatest happiness" may infringe any one of the five basic values.
A more "liberal" strain of istislah has been important in the 20th century and centres on the work of Rashid Rida, who considered that the "no harm no retribution" hadith the supreme principle of legal liberalism, trumping all other principles of Shariah. Rida made istislah "a central rather than subsidiary principle for defining the law...[which] makes adaptions more flexible". By this method, some human rights can be considered "Islamic". In Egypt this approach has been upheld by the Supreme Constitutional Court, which has ratified equitable measures benefiting women even where these seemingly conflict with principles of classical Shari'ah.
- Mawil Izzi Dien. Islamic Law: From Historical Foundations to Contemporary Practice. p. 69.
- Knut S. Vikør (2005). Between God and the Sultan: A History of Islamic Law. Oxford University Press. p. 234–35. ISBN 9780195223989.