Unattested interest (al-maslaha al-mursala, istislah)

An unattested interest (al-maslaha al-mursala), acting on which is called istislah, is an interest for which no specific text of the law testifies either for or against. ¹ Al-Ghazali, in al-Mustasfa, counts it as the fourth of the "supposed sources", after the law of earlier prophets, the Companion's opinion and istihsan. ^{2 1}

Al-Ghazali divides interests, by the law's testimony, into three: ¹

• Those the law confirms: a proof, reducing in effect to analogy - for example forbidding every intoxicant by analogy with wine, forbidden to protect the intellect on which legal responsibility rests. ¹
• Those the law cancels: for example a scholar who told a king who had had intercourse during a day of Ramadan to fast two consecutive months rather than free a slave, on the grounds that manumission would be too easy for him; al-Ghazali holds this void and contrary to the text of the Book, and says opening this door would let the law's limits change with circumstances. ¹
• Those for which no specific text testifies either way: these are open to reasoning. ¹

Al-Ghazali says that interest originally means securing benefit or warding off harm, but that is not what he means, since those are the purposes of creatures; he means preserving the purpose of the law, and the law's purpose for creation is five: to preserve their religion, life, intellect, progeny and property; whatever secures these five is an interest, whatever loses them is harm, and warding harm off is an interest. ^{1 3} He ranks interests by strength into necessities, needs and refinements, each with its complement, illustrating needs by the guardian's authority to marry off a minor girl and refinements by denying a slave the capacity to testify. ^{1 3} See: The five necessities.

Al-Ghazali holds that what falls in the tiers of needs and refinements cannot by itself ground a ruling unless supported by a base - in which case it is analogy - while what falls in the tier of necessities may be reached by a mujtahid's reasoning even without a specific base. ⁴ He requires that it be necessary, certain and universal, illustrated by the "shield" case: if unbelievers shield themselves with Muslim captives and holding back would certainly lead to the extermination of the Muslims, one might say that preserving all the Muslims is closer to the law's purpose; he excludes cases that differ - a shield in a fortress (not necessary), people in a boat throwing one overboard (not universal), people starving. ⁴ He then says the question is "open to ijtihad" and that "forbidding it is not far-fetched", noting that the Iraqi authorities of his school gave two views on it. ⁵

• Beating a suspect to make him confess to theft is an interest Malik accepted; al-Ghazali does not, because it is opposed by the interest of the one beaten, who may be innocent. ⁴
• When the treasury cannot pay the army and an enemy invasion is feared, he allows the ruler to levy on the rich what the army needs, since the law aims to ward off the greater of two harms. ⁵
• He explains the Companions' raising the penalty for drinking to eighty as concerning a penalty that was not fixed, brought close to the penalty for slander because drinking is a likely cause of false accusation - so it was not overriding a text by interest. ⁶

Al-Ghazali holds that istislah is one of the supposed sources, and that whoever thinks it a fifth source after the Book, the sunna, consensus and reason is mistaken, since interest is traced back to preserving the law's purposes, which are known from the Book, the sunna and consensus; any outlandish interest that does not return to them is void, and "whoever adopts it has legislated, just as whoever practises istihsan has legislated". ⁶ He adds that once interest is understood as preserving the law's purpose there is no ground for dispute about following it - it must be held a proof - and disagreement arises only when two interests conflict; it is called "unattested" because these meanings are known to be intended through countless indications rather than a specific base. ⁷

Imam al-Haramayn al-Juwayni, al-Ghazali's teacher, reports three positions on "inference" (istidlal), a closely related notion, in al-Burhan; see: Is unattested inference a valid proof? ^{8 9}

The Maliki and Hanbali accounts of unattested interests from their own books, and modern studies, are not given here.