Some scholars have said that the capacity to be stored is a necessary condition for the prohibition of excess within a single genus, whereas the ban on deferment in such items rests on their being both edible and storable.

We have already stated that, taken absolutely, edibility is the operative cause for prohibiting deferment (nasīʾah) in all foodstuffs.

As for the Shāfiʿīs, the factor that forbids excess (tafāḍul) in these four staples, in their view, is simply edibility—provided the two lots belong to the same genus. The cause that forbids deferment is likewise edibility, without regard to sameness of genus, exactly as Mālik maintained.

The Ḥanafīs, by contrast, hold that the single cause barring excess in the six items is their being sold by measure—whether by volume or by weight—when the genus is identical. The cause that bans deferment among them is difference of genus, save in the case of copper and gold, for consensus has been reached that deferment is permissible in those two. Shāfiʿīs agree with Mālik concerning the cause that forbids both excess and deferment in gold and silver—that is, their serving as the principal media of exchange and the standard of indemnities; in their judgment this forbids deferment when the genera differ, and excess when they are the same.

The Ḥanafīs further stipulate, for anything sold by volume, that the quantity exchanged be such as can in fact be measured by volume. The specific rulings governing gold dinars and silver dirhams will be treated, in their proper place, in the Book of Currency Exchange (Kitāb al-Ṣarf). For the moment, our purpose is merely to set out the jurists’ various views on the underlying causes of the general prohibition of ribā in these items and to cite the main evidence upon which each school relies.

We therefore say: Those who confine the category of ribā to these six items fall into one of two groups. The first comprises those who reject analogical reasoning (qiyās) in the Sharīʿah altogether—that is, the derivation of legal causes from the wording of the texts—namely the Ẓāhirīs. The second comprises those who deny analogy based on resemblance (qiyās al-shabah); for anyone who extends the ruling here from what is explicitly mentioned to what is left unmentioned does so by resemblance rather than by identifying a common legal cause, save for what is reported from Ibn al-Mājishūn, who took monetary value into account and said that the rationale for forbidding ribā is the safeguarding of wealth, meaning the protection of the very substance of property.

As for Qāḍī Abū Bakr al-Bāqillānī, considering analogy of resemblance weak and analogy of meaning stronger, he resorted to analogy of meaning here, since no causal analogy was available to him. He therefore attached only raisins to the four foodstuffs, claiming that they are equivalent to dates. Each of these scholars who employs analogy has his own proof for the resemblance he cites when annexing an unmentioned item to one of the four.

The Shāfiʿīs, for their part, maintain in defense of their resemblance-based cause that whenever a ruling is linked to a derived noun, this shows that the attribute from which the noun is derived constitutes the legal cause for the ruling—just as the Almighty says: “As for the thief, male or female, cut off their hands” (Q 5:38). Because the ruling is attached to the derived noun “thief,” it is evident that the ruling pertains to the very act of theft.

They add: If this is so, and if the ḥadīth narrated by Saʿīd ibn ʿAbd Allāh states, “I used to hear the Messenger of Allah—peace and blessings be upon him—say: ‘Food for food, like for like,’” then it is manifest that edibility is the attribute to which the ruling has been attached.

As for the Mālikīs, they added to edibility one further attribute—namely storability, according to what is recorded in the Muwaṭṭaʾ, or else