2/275-276 — Ribā: where two transactions part
"Those who eat ribā rise only as one rises whom Satan has struck down. That is because they say 'trade is just like ribā'. But God has made trade lawful and ribā forbidden."
رِبَا — root ر-ب-و: to increase, to rise, to swell. From the same root come rabwa (high ground — it occurred at verse 265) and tarbiya (nurture). The word itself means "increase"; what is forbidden is not increase itself but which transaction it arises from — indeed the same verse counts the profit in trade lawful.
The objection itself is reported in the verse: innama'l-bayʿu mithlu'r-ribā — "trade is just like ribā." The other side, that is, looks at the outcome of the two transactions and counts them the same: in both the money increases.
The answer looks not to the outcome but to the structure of the transaction. It is transmitted that in the classical commentaries the distinction is set up at these points: in trade a good changes hands, there is risk, one of the parties may lose; in ribā the increase is fixed from the outset according to time and the risk stays on one side.
I transmit this as the explanations made within the tradition and issue no legal ruling; the scope of ribā and its application to contemporary transactions is a separate debate, and there are differences among the schools.
The word order turns things round, and it does so with the words themselves: the verb yurbī is from the same root as ribā. For the thing that bears the name "increase" the verb of diminution is used, and for giving without return the verb of increase. The verse exchanges the names of the two transactions.
مَحْق — the wiping out of a thing's blessing, its vanishing by degrees. The lexicographers call the last phase of the moon miḥāq too: what diminishes while it shows.