but disparity in amount is permissible, and the parties may separate before taking possession. What is meant here, however, is the narrower genus—that is, the most specific genus. If we wish to avoid the terminology and conventions of the speculative theologians, we may simply say: wheat, dates, barley, salt, gold, and silver. There is no need to speak of the broader genus and the narrower genus, for this may confuse people.

Accordingly, when we say that a ribā-based commodity may not be sold for another of its own genus, what this means is that wheat may not be sold for wheat. Barley, however, is an independent genus. Thus, if you wish to sell wheat for wheat, two things are obligatory:

First: reciprocal possession before the parties separate.

Second: equality according to the legally prescribed measure.

If you wish to sell wheat for barley, then only one thing is obligatory: reciprocal possession before the parties separate.

His statement, “The derivatives of genera—such as flours, breads, oils, and meat—are distinct genera according to their respective origins,” means that the derivatives of genera are themselves genera. But are they independent genera, or are they genera subordinate to their origins?

The author—may Allah have mercy on him—indicates here that they are genera subordinate to their origins. Accordingly, if whole wheat is sold for wheat flour, this is not permissible because equality cannot be established. Once the grain is ground, it spreads out, and it cannot be measured by volume; nor can it be measured by weight, because wheat may only be sold for wheat by volume.

If whole wheat is sold for barley flour, it is permissible without measuring by volume or weight, because wheat may be sold for barley in unequal amounts. Flour is a genus by virtue of its origin.