If, for example, a man were to sell a horse for garments, equity would require that the ratio of that horse’s value to horses in general equal the ratio of those garments’ value to garments in general. Thus, if the horse is worth fifty, the garments must likewise be worth fifty. Suppose that sum is reached with ten garments; the difference in number between the two things sold is then of no consequence, so long as justice in the transaction is observed—meaning that, in this case, the fair equivalent of one horse is ten garments of comparable quality.
As for commodities that are sold by measure or by weight: because they do not differ greatly from one another and their utilities are nearly the same, a person who possesses one variety has no pressing need to exchange it for that very same variety except out of sheer desire for gain. Equity here, therefore, lies in exact equality of volume or weight, since their benefits do not vary. Moreover, to forbid disparity (tafāḍul) in such items would lead to little or no trade in them at all, for their utilities are homogeneous and trade is only resorted to when utilities differ. Accordingly, the prohibition of disparity in these commodities—that is, in those that are measured or weighed—rests on two reasons:
- The existence of equity among them; and
- The need to block transactions that would amount to profiteering.
With respect to the dinar and the dirham, the rationale for prohibition is even clearer, for these coins are not sought for profit in themselves; their purpose is simply to serve as standards for valuing goods that have indispensable utilities.
Mālik transmitted from Saʿīd ibn al-Musayyib that he regarded the operative cause of ribā in these categories to be both measurement by volume and edibility. This is a sound observation, for food is essential to the sustenance of humankind. It therefore makes sense that preserving the principal and preventing usurious gain in staple nourishment is more critical than in things that are not staples. Some of the Successors took the operative cause of ribā to be any category of wealth on which zakāt is due, while others considered it to be benefit in the absolute sense—that is, monetary value; this last view was adopted by Ibn al-Mājishūn.
Section Two
Identifying the items in which excess is permissible but deferred exchange (nasī’ah) is not
From this it follows that, according to Mālik and al-Shāfiʿī, the factor that prohibits nasī’ah in the ribā commodities is edibility. As for non-ribā commodities that are not foodstuffs, Mālik holds that the bar to nasī’ah is their being of a single genus with identical utilities while disparity exists, whereas al-Shāfiʿī recognizes no nasī’ah outside the ribā commodities. Abū Ḥanīfa, by contrast, attributes the prohibition of nasī’ah to measurability by volume in the ribā commodities, and to sameness of genus in non-ribā commodities—whether or not disparity is involved. A report transmitted by Ibn al-Qāsim from Mālik may suggest that he too forbids nasī’ah in these cases, because he considers it a form of salam (advance-payment sale) that brings a benefit to one of the parties.