כל הנישום דמים באחר כיון שזכה זה נתחייב זה בחליפין
With regard to all items that can be appraised when used as monetary value for another item, i.e., their value can be appraised relative to the value of another item, excluding a coin, whose value is apparent, once one party in the transaction acquires the item he is receiving, this party is obligated with regard to the item being exchanged for it. The novelty of the mishna is that all items, not only vessels, can be used to perform the act of acquisition of exchange. Therefore, one should not infer that the halakha is the same with regard to coins.
ה"נ מסתברא מדקתני סיפא כיצד החליף שור בפרה או חמור בשור שמע מינה
The Gemara comments: So too, it is reasonable to interpret the mishna in that manner, from the fact that the latter clause of that mishna teaches: How so? If one exchanges an ox for a cow, or a donkey for an ox, once this party acquires the animal that he is receiving, this party is obligated with regard to the item being exchanged for it. This clause apparently explains the previous clause, and employs the example of animals, not coins. The Gemara concludes: Learn from it that the reference in the mishna is to movable property, not to coins.
ולמאי דסליק אדעתיה מעיקרא מטבע מאי כיצד הכי קאמר ופירי נמי עבדי חליפין כיצד החליף שור בפרה או חמור בשור
The Gemara asks: And with regard to what entered our minds initially, that a coin effects symbolic exchange, what is the meaning of the clause: How so; if one exchanges an ox for a cow, once this party acquires the animal that he is receiving, this party is obligated with regard to the item being exchanged for it? This example does not involve a coin. The Gemara explains that it was assumed that this is what the mishna is saying: Not only can a coin be used in the act of acquisition of exchange, but produce, i.e., movable property, can also effect exchange. How so? If one exchanged the meat of an ox for a cow, or the meat of a donkey for an ox, once this party acquires the item that he is receiving, this party is obligated with regard to the item being exchanged for it.
הניחא לרב ששת דאמר פירי עבדי חליפין אלא לר"נ דאמר כלי אין אבל פירי לא עבדי חליפין מאי כיצד
The Gemara comments: This works out well according to the opinion of Rav Sheshet, who said: Produce effects a transaction of exchange. But according to the opinion of Rav Naḥman, who said: A vessel, yes, it effects a transaction of exchange, but produce does not effect a transaction of exchange, what is the meaning of the continuation of the mishna beginning with the question: How so?
הכי קאמר יש דמים שהן כחליפין כיצד החליף דמי שור בפרה או דמי חמור בשור
The Gemara answers that this is what the mishna is saying: There is a purchase with money where one acquires the purchase item without pulling it that is like a transaction of exchange. How so? It is in a case where one exchanged the monetary value of an ox for a cow, or the monetary value of a donkey for an ox. In this case, one sold his ox to another for an agreed sum of money, and after the buyer acquired the ox by pulling it, he then offered to give the seller his cow in exchange for the money that he owes him. In this case the cow is acquired without the seller having to pull it. Although this acquisition initially was to be an exchange, it is ultimately a purchase for money, as the second animal is acquired as a result of the forgiving of the monetary debt.
מאי טעמיה דרב נחמן סבר לה כרבי יוחנן דאמר דבר תורה מעות קונות ומפני מה אמרו משיכה קונה גזירה שמא יאמר לו נשרפו חטיך בעלייה
The Gemara inquires: What is the reason for the opinion of Rav Naḥman? The Gemara explains: Rav Naḥman holds in accordance with the opinion of Rabbi Yoḥanan, who says: By Torah law money effects acquisition, i.e., when one pays money he acquires the item, even if he has not yet performed another act of acquisition. And for what reason did the Sages say that pulling acquires an item and money does not? This is a rabbinic decree lest the seller say to the buyer after receiving the money: Your wheat was burned in the upper story. If a fire breaks out or some other mishap occurs after a seller receives the money, he will not bother to save the goods in his house because they no longer belong to him, and the buyer may incur a loss.
ומלתא דשכיחא גזרו ביה רבנן מלתא דלא שכיחא לא גזרו ביה רבנן
The Sages therefore decreed that acquisition takes effect only when a buyer pulls the item. The mishna allows a transaction that indicates that one can effect acquisition using only money because that case of the mishna as explained by Rav Naḥman is an uncommon occurrence. It is rare for one who has sold his animal in exchange for money to change his mind and request an animal from the purchaser instead. And it is only with regard to a common matter that the Sages issued a decree, whereas with regard to an uncommon matter, the Sages did not issue a decree. Consequently, the Sages did not apply their decree to this situation.
ולריש לקיש דאמר משיכה מפורשת מן התורה הניחא אי סבר לה כרב ששת מתרץ לה כרב ששת
The Gemara asks: And how is the mishna explained according to the opinion of Reish Lakish, who disagrees with Rabbi Yoḥanan and says that pulling is explicitly stated in the Torah? Reish Lakish maintains that the acquisition of movable property cannot be performed with money by Torah law, and therefore there can be no distinction between common and uncommon cases. This works out well if Reish Lakish holds in accordance with the opinion of Rav Sheshet, who says that produce effects exchange. If so, he can explain the mishna in accordance with the opinion of Rav Sheshet.
אלא אי סבר לה כרב נחמן דאמר פירי לא עבדי חליפין ומטבע לא קני היכי מתרץ לה על כרחך כרב ששת מתרץ לה
But if he holds in accordance with the opinion of Rav Naḥman, who says that produce does not effect exchange and a coin does not effect acquisition by Torah law or by rabbinic law, how does he explain the mishna? The Gemara answers: Perforce Reish Lakish explains the mishna in accordance with the opinion of Rav Sheshet.
תנן כל המטלטלין קונין זה את זה ואמר ריש לקיש ואפילו כיס מלא מעות בכיס מלא מעות תרגמא רב אחא בדינר אנקא ואניגרא אחד שפסלתו מלכות ואחד שפסלתו מדינה
We learned in the mishna: With regard to those who exchange all forms of movable property, each acquires the property of the other. And Reish Lakish says: The expression: All forms of movable property, includes even a case where they exchange a money pouch full of coins for a money pouch full of coins. Apparently, coins effect exchange and are acquired by means of a transaction of exchange. The Gemara rejects this: Rav Aḥa interpreted that the exchange of coins is referring to the exchange of a money pouch filled with anka dinars and a money pouch filled with anigera dinars. One is a coin that the kingdom invalidated, as the king decreed that the coin will no longer be used, and one is a coin that the residents of a province invalidated, as they no longer use it as currency.
וצריכא דאי אשמועינן פסלתו מלכות משום דלא סגי כלל אבל פסלתו מדינה דסגי ליה במדינה אחריתי אימא אכתי מטבע הוא ואין מטבע נקנה בחליפין
And it is necessary to teach the halakha in both cases, as, if the tanna taught us this halakha only with regard to a coin that the kingdom invalidated, I would have said it is not a coin due to the fact that it does not circulate at all, as the king banned its use. But with regard to a coin that the residents of a province invalidated, which circulates in a different state, say that its legal status is still that of a coin, and money cannot be acquired by means of a transaction of exchange.
ואי אשמועינן פסלתו מדינה משום דלא סגי ליה לא בצנעא ולא בפרהסיא אבל פסלתו מלכות דסגי ליה בצנעא אימא אכתי מטבע הוא ואין מטבע נקנה בחליפין צריכא
And if the tanna taught us this halakha only with regard to a coin that the residents of a province invalidated, I would have said it is not a coin due to the fact that in that place it neither circulates in private nor in public, as the local residents do not use it as currency. But with regard to a coin that the kingdom invalidated, which could circulate in private, say that its legal status is still that of a coin, and money cannot be acquired by means of a transaction of exchange. Therefore, it was necessary to teach the halakha in both cases.
אמר רבה אמר רב הונא מכור לי באלו קנה
§ Rabba says that Rav Huna says: If one said to another: Sell me your item for these coins that are in my hand, and when taking the money the owner of the item did not determine the sum, the buyer acquired the article and the transaction is complete, and neither can renege on the deal.