Paper currency has some resemblance to the two metals (gold and silver), and some resemblance to trade goods

The Shaykh : No, no, we said they are not trade goods. They have some resemblance to trade goods in one respect, because their value fluctuates, and they have some resemblance to the two metals in one respect, because they are the measure of the value of things. Now, are trade goods the measure of the value of things, or are they something else? Something else. These papers resemble the two metals in that they are the measure of the value of things, and they resemble trade goods in that they increase and decrease. So we say: we use the most cautious approach for the person, and we treat them as currency, and zakah is obligatory on them. If we said they are trade goods and zakah is not obligatory on them, that would mean they are not currently...