Mishnah 11 returns to the tractate's usual format - disputes between Beis Shammai and Beis Hillel. The subject before us continues the laws of Ma'aser Sheni, and its focus is the changing of a coin that a person brought up to Jerusalem into smaller coins.
The concern underlying the dispute:
The small coins are made of copper, and copper does not have the longevity of silver: it oxidizes, turns green, and eventually crumbles and disintegrates until it is no longer money at all. A person who changes his silver coin into copper coins may not use all of them to buy food in Jerusalem, and he will be left with leftovers. He will not convert them back into silver so as to change them again the next time; instead he will deposit them in the bank or leave them with his cousin in Jerusalem - and in the meantime they will rust, become damaged and wear out until they are unusable. The result is that he will have less money with which to buy Ma'aser Sheni, and he will eat less Ma'aser Sheni, and that is what we want to prevent. Hence the question: what portion of the sela may be changed into copper, lest leftovers remain and go to waste?
The language of the Mishnah:
"HaPoret sela shel ma'aser sheni b'Yerushalayim" - one who changes a sela, which is a large silver coin, into coins smaller than it, in Jerusalem. Here the word "poret" is used in its ordinary sense, unlike in the previous Mishnah.
The opinions of the Tanna'im are arranged from the most lenient to the most stringent:
"Beis Shammai omrim: b'chol hasela ma'os" - one may change the entire sela into small coins, and receive in exchange for one silver sela seven hundred and sixty-eight tiny copper perutos. Beis Shammai are here the most lenient - something uncharacteristic, and nevertheless so it is: permission is granted to change the whole of it.
"U'Veis Hillel omrim: b'shekel kesef u'v'shekel ma'os" - a sort of compromise, half and half: the value of a shekel, which is half the sela, remains in silver, and the second shekel, the other half, is changed into ma'os - small copper coins. And since he changes less, there is less chance that a surplus will remain and ultimately be lost.
"HaDanin lifnei chachamim omrim: dinarim kesef... dinar ma'os" - in their view one may change only a quarter. There are four dinars in a sela, and the dinar too is a silver coin: three of the four dinars remain silver dinars, and the value of the fourth dinar he changes into copper coins.
"HaDanin lifnei chachamim" (those who deliberate before the Sages) is a special expression, and it refers to four or five of the Tanna'im who did not live long enough to receive semichah and the title "Rabbi," and nevertheless carried great weight in the period of the Mishnah. They are: Shimon ben Azzai, Shimon ben Zoma, Chananya the Egyptian and Chananya ben Teradyon, and according to certain opinions a fifth as well - Shimon HaTimni.
"Rabbi Akiva omer: dinarim kesef... ma'os" - Rabbi Akiva is more stringent: three dinars of the sela remain silver, and even of the fourth dinar he may change only a quarter into copper coins, while the remaining three quarters also stay in silver. The result is that three dinars and three quarters of a dinar remain in silver, and a quarter of a quarter - which is one sixteenth - goes to copper.
"Rabbi Tarfon omer: asper kesef" - more stringent still: only one twentieth, five percent, is changed into copper. Three quarters of the sela remain in silver, and of the fourth dinar one converts only the value of a single asper into ma'os. The asper is a common Greek coin, and there are five aspers in one dinar; the remaining four aspers stay as silver. And a fifth of a quarter is one twentieth.
Shammai's opinion - the most stringent of all:
Shammai himself says that one does not change coins at all. His concern is twofold. The first concern is the one shared by all the opinions: the small coins are liable to corrode and be ruined if they are not converted back, and we do not want things to be lost for nothing.
But there is a second concern, and because of it any amount of changing is problematic: Ma'aser Sheni money may be spent only on food products and things needed by the body - food, drink or oil for anointing - and one may not pay with it for a taxi or a hotel bill. And what will happen? A person will arrive in Jerusalem, change his silver sela into copper coins, and they will be sitting in his pocket. He will take a taxi to the hotel and be asked to pay, and all he has in his pocket is Ma'aser Sheni money, and he is liable to spend it by mistake or even deliberately - and that is forbidden.
Therefore Shammai says: "Yanichenah ba'chanus v'yochal k'negdah" - one does not change the coin into small coins that are liable to get mixed in and spent by mistake; rather one gives the entire Ma'aser Sheni coin to the shopkeeper, and a credit is recorded against it to be drawn down. True, it is possible that the shopkeeper does not know the buyer, since he has come from another city, and will not extend him credit; but once he has placed the coin in his hand and said, "Here is the coin before you, and I need to spend against it - and whatever I buy in your shop will be deducted from the value of the Ma'aser and redeemed onto the goods," it is effective, for he is redeeming it onto food items.
The same applies if he gives the coin to the wine seller, if it is drink that he is buying, or to the baker, if it is bread onto which he is redeeming. And the essential point is this: the shopkeeper will deduct piece by piece, and the buyer will eat against it and consume his food and drink while deducting from the value of the coin according to what he buys and consumes. And at the end of his stay, whatever remains and was not used the shopkeeper will return to him in coins, and these coins carry the sanctity of Ma'aser Sheni, and he will keep them until the next time.
The halachah: The ruling follows Beis Hillel - half and half. One who changes his silver coins into copper coins may change only half into copper, while the other half remains in silver.