1) REPAYING A LOAN OF GOLD COINS WITH GOLD COINS
QUESTION: The Gemara relates that Rav borrowed gold coins from the daughter of Rebbi Chiya. Later, when the value of gold appreciated in relation to the value of silver, Rav asked Rebbi Chiya if he was permitted to pay back the same number of gold coins that he borrowed. Rav's question was based on the issue of whether gold is considered a currency or a commodity. If it is considered a currency, it would be permitted to return the same number of coins, and such a repayment would not be considered Ribis. On the other hand, if gold is considered a commodity (merchandise), Rav would have been required to repay only the value of the gold coins in silver at the time they were borrowed. He would not have been permitted to return the same number of gold coins that he had originally borrowed; since those gold coins could be used to acquire more silver coins, returning the same number of gold coins would have constituted Ribis. Rebbi Chiya ruled that Rav may pay back the full amount of gold, because gold is considered currency in relation to silver.
Rav did not ask Rebbi Chiya whether he was permitted to borrow the gold coins in the first place with intent to pay back the same coins later. Only when it was time to pay back did he ask how he may pay back the loan. Why did Rav not ask Rebbi Chiya whether he was permitted in the first place to borrow the gold coins with intent to pay back the same coins later? Indeed, Rebbi Yochanan teaches (beginning of 45a) that one is prohibited even to borrow a gold coin with intent to pay the lender back with a gold coin!
(a) The RITVA cites his "teacher's teacher" (the RAMBAN) who explains that Rebbi Yochanan does not mean that borrowing a gold coin with intent to return a gold coin is prohibited. Rather, his statement should be interpreted to mean that one is prohibited to borrow a gold coin if one pays back a gold coin after gold appreciates. The prohibition applies only at the time that the loan is repaid. The HE'OROS B'MASECHES BAVA METZIA adds that even if one normally is prohibited to borrow a gold coin with the explicit intention to pay back a gold coin, Rav might have permitted it in this case. This is because the prohibition to pay back a gold coin is mid'Oraisa, but the prohibition to stipulate that the loan will be repaid in gold (even if the market price of gold changes) is mid'Rabanan. Since Rav was unsure of whether or not gold is considered a commodity (in which case the laws of Ribis are applicable), he was lenient with regard to the Isur mid'Rabanan, and he asked Rebbi Chiya only for permission to repay when there was a possible Isur mid'Oraisa involved.
(b) The RITVA himself suggests that Rebbi Yochanan in fact does prohibit even borrowing a gold coin, but only if it is stipulated explicitly that the borrower will repay a gold coin even if gold appreciates. When Rav borrowed gold coins, he did not stipulate that he would pay back an equal amount of gold even if it would appreciate. Therefore, he was permitted to borrow the gold. His only question was how he should repay it after the gold appreciated. Although he did not stipulate that he would pay back an equivalent amount of gold coins, nevertheless if gold would have appreciated, it would have been prohibited for him to pay back gold coins that were worth more than the coins that he borrowed. (The TAZ (YD 162:103) and the RASHASH suggest the same answer.)
The Ramban, who does not accept this answer, might have reasoned that if Rav had not stipulated at the time of the loan that he would pay back the same number of gold coins, then he would have been permitted to pay back the lesser amount of silver when the price of gold fluctuated. From the fact that Rebbi Chiya told Rav to pay the full amount, it is clear that Rav in fact did stipulate that he would repay the same number of gold coins that he borrowed.
(c) The RASHBA writes that at the time that Rav borrowed the money, he was confident that gold was considered currency and not merchandise. Later, when the time came to repay, he had doubts, and therefore he went to ask Rebbi Chiya.
2) THE CURRENCY OF PIDYON HA'BEN
QUESTION: The Gemara discusses whether a gold coin, when compared with silver, is considered a currency or a commodity. The Gemara cites proof from a Beraisa which states that there are 25 Dinarim of silver in one Dinar of gold (that is, one Dinar of silver is worth 1/25th of a Dinar of gold). The practical ramification of this value is how much one must pay for Pidyon ha'Ben. The amount of money necessary for Pidyon ha'Ben is always linked to the value of gold and not to the value of silver. The Gemara proves conclusively from this Beraisa that gold is considered a currency, and if the value of silver changes in relation to gold, the value of gold determines the amount given to the Kohen for Pidyon ha'Ben.
How can the value of Pidyon ha'Ben be determined by the value of gold and not by the value of silver? The Torah specifically states that the amount that must be paid for Pidyon ha'Ben is "Kesef Chameshes Shekalim b'Shekel ha'Kodesh, Esrim Gerah Hu" -- five silver Shekalim, which are twenty Gerah (Vayikra 18:16)! (RITVA)
ANSWER: The RITVA and TOSFOS HA'ROSH answer that if silver is considered merchandise and not currency in relation to gold, then it is logical to assume that the Torah would not link the value of Pidyon ha'Ben to the price of an entity with a fluctuating value (i.e. merchandise). Rather, the Torah mentions five Shekalim of Kesef only because that was the equivalent of four-fifths of a Dinar of gold at the time the Torah was given. The real price of Pidyon ha'Ben, however, is not five Shekalim of Kesef but the equivalent of that amount in gold, at the time of the giving of the Torah. The Chachamim had a tradition that the amount of gold equal to five Shekalim of silver was four-fifths of a Dinar of gold.
TOSFOS RABEINU PERETZ adds that this is what the Torah means when it links the Shekel of Pidyon ha'Ben to a Gerah (according to the opinion that gold is considered currency in relation to silver). The Gerah was a coin that was linked to the price of gold and not to the price of silver. The Torah is saying that the price of Pidyon ha'Ben is not really linked to the value of five silver Shekalim, but rather to the value of twenty Gerah. The TARGUM ONKELUS writes that twenty Gerah is twenty "Ma'in," but that is not meant as a literal translation of Gerah, because "Ma'in" are silver coins. Rather, he converts the Gerah to a coin which was common in his time, which was made of silver and which was worth the same amount at that time.