The cause of ribā in gold and silver and its influence on trading

Ribā (usury) is absolutely prohibited in Islam. The Hadiṯ enumerated six commodities on which ribā applies (ribawī commodities): gold, silver, wheat, barley, dates, and salt. The scholars of the four schools of Islamic Jurisprudence agreed, however, that ribā applies also to other commodities that share the cause with the six commodities enumerated in the Hadiṯ. This paper investigates (a) the cause of ribā in gold and silver and (b) the consequence of adopting the ṯamaniyah (the intrinsic value of a commodity) cause on selling gold for gold with excess if manufacturing or workmanship of the two varies. This research concludes that the cause of ribā al-nasīʾah (usury in credit transactions) in gold and silver is the ṯamaniyah, i.e., the gold and silver being commodities with intrinsic value, and that the cause of ribā al-faḍl (excess in the exchange of the same commodity) in gold and silver is the ṯamaniyah and the homogeneity of the commodity traded (i.e., gold for gold or silver for silver). It is obligatory that gold is traded in equal weights even if raw or money gold is exchanged for gold jewelry or vice versa. This does not cause hardship on people, however, because trading nowadays is done using fiat money (each currency of which is considered a different sort) and, therefore, people can buy and sell gold for any price of fiat money agreed upon, provided that the price is paid immediately and on the spot