Bava Mezia page 46 side a and b. The Mishna says, “All that is made monetary value in another, once one acquires it, the other acquires its exchange. How is this. if one exchanges an ox for a cow, once one acquires one, the other acquires the other.” The gemara asks that it seems the Mishna means that a coin can cause exchange, (and we know that is not the case). So Rav Juda says it means if one evaluates an object once one acquires the first the other acquires tthe second. [ie that exchange needs evaluation.] the gemara asks tat this point that the hava amina (I would have thought) was at least true according to Levi that holds a coin can cause exchange. So how did the Gemara understand the Mishna at that point? After all, the example it gives has no relevance to coins. (The example is a cow and for an ox) Answer. The mishna means coins can cause exchange, and fruit also. (The example of a ox for a cow is an example of fruit.) But to Rav Nachman who holds fruit can not cause exchange, what could the Mishna mean? Here Tosphot asks on Rabainu Tam that perhaps the Mishna in Kidushin page 28 is talking about exchange equal for equal, and in that case fruit can cause exchange according to Rabbainu Tam. He answers that that can not be so, since the end of the mishna has to be like the beginning, and the beginning is clearly not equal for equal. I fail to see why this is so. according to the I would have thought (hava amina) we arre talking about the law that a coin can be exchanged. ''All that is made money value for something else, once one acquires the object, the other acquires the exchanged object. '' Where do we see here that it is not talking about equal for equal? A possible answer to this is that Tosphot understands Rav Juda to mean that the exchange has to be equal for equal and therefore the I would have thought has to mean that coin can cause exchange even when it is not equal for equal.-------------------------------------------------------------------------------------------------------------------- ---- בבא מציעא page מ''ו ע''א וע''ב. The משנה says, “All that is made monetary value in another, once one acquires it, the other acquires its exchange. How is this. if one exchanges an ox for a cow, once one acquires one, the other acquires the other.” The גמרא asks that it seems the משנה means that a coin can cause exchange, (and we know that is not the case). So רב יהודה says it means if one evaluates an object once one acquires the first, the other acquires the second. [ie that exchange needs evaluation.] The גמרא asks at this point that the הווה אמינא (I would have thought) was at least true according to לוי that holds a coin can cause exchange. So how did the גמרא understand the משנה at that point? After all, the example it gives has no relevance to coins. (The example is a cow and for an ox) Answer. The משנה means coins can cause exchange, and fruit also. (The example of a ox for a cow is an example of fruit.) But to רב נחמןwho holds fruit can not cause exchange, what could the משנה mean? Here תוספות asks on רבינו תםthat perhaps the משנה in קידושין page כ''ח is talking about exchange equal for equal, and in that case fruit can cause exchange according to רבינו תם . He answers that that can not be so, since the end of the משנה has to be like the beginning, and the beginning is clearly not equal for equal. I fail to see why this is so. according to the I would have thought (הווה אמינא) we are talking about the law that a coin can be exchanged. ''All that is made money value for something else, once one acquires the object, the other acquires the exchanged object. '' Where do we see here that it is not talking about equal for equal?A possible answer to this is that תוספות understands רב יהודה to mean that the exchange has to be equal for equalת and therefore the ''I would have thought'' has to mean that coin can cause exchange even when it is not equal for equal.