The operative cause of riba in gold, silver, and the four categories

The questioner:
Honorable Shaykh, I ask you to clarify the correct evidence regarding gold and silver, and wheat, barley, and fruit.

The Shaykh:
Give it to them.

The questioner:
I ask you to clarify the correct evidence regarding gold and silver, and wheat, barley, and fruit.

The Shaykh:
The stronger position is that the operative cause in gold and silver as currency is their being the most valuable, or their being currency. This is the operative cause in gold and silver. Everything considered currency is measured by this, including the paper money known today, namely paper currency. As for the operative cause in wheat, barley, dates, and salt, it is being food combined with being measured by volume. Being food combined with being measured by volume means being measured by volume and being food, that is, foods eaten as foods. The combination of these two descriptions, being food combined with being measured by volume, is the stronger position. Yes.