They therefore added two qualities—storability and suitability as a staple—according to the view adopted by the scholars of Baghdad. They support this derivation by arguing that, had mere edibility been the objective, a single one of the four commodities would have sufficed to alert us to it. The fact that several were named shows that each was meant to point to everything of the same nature, and what unites them all is that they can be stored and serve as basic nourishment. Thus, by mentioning wheat and barley the Lawgiver alluded to every stored grain; by mentioning dates He alluded to every stored sweetness such as sugar, honey, and raisins; and by mentioning salt He alluded to every stored seasoning used to prepare food.
They also say: because the discernible rationale for prohibiting ribā is to prevent people from defrauding one another and to safeguard their property, the prohibition must apply to the foundations of livelihood—namely staple foods.
As for the Ḥanafīs, their chief proof for attaching the ruling to whatever is measured by volume or by weight is that the Prophet—may Allah bless him and grant him peace—made permissibility contingent upon sameness of genus and sameness of quantity, while he made prohibition contingent upon sameness of genus and difference of quantity. This is evident in his instruction to his revenue officer in Khaybar, related by Abū Saʿīd and others: “ … except measure for measure, hand to hand.” They therefore held that quantification—whether by volume or by weight—is an operative cause equivalent to sameness of genus. At times they cite several little-known ḥadīths that give strong support to considering volume and weight, among them versions which add, after the commodities named in the ḥadīth of ʿUbādah, the words: “and likewise whatever is measured by volume or by weight,” and others that read: “and likewise the measuring vessel and the scale.” Were these reports sound, they would constitute an explicit text. Yet even when one reflects on the matter purely in terms of underlying meaning, it appears—Allah knows best—that their cause is the most compelling. The Sharīʿah makes it clear that the purpose of forbidding ribā is to eliminate the considerable inequity it entails, and that justice in transactions lies in approximating equality. Because attaining strict equality in commodities of differing natures is difficult, the dinar and the dirham were instituted to value—i.e., to appraise—them. As for items of disparate natures that are neither weighed nor measured, equity is achieved by maintaining proportion—meaning that the ratio of one article’s value to others of its kind should equal the ratio of the other article’s value to others of its kind. For example, justice would be attained if a man were to sell