I wondering why the Rambam decide a law like the O would have said” instead of the conclusion of the Gemara in Kidushin pg 28. the answer I think is that the conclusion of the gemara is going like Rav Joseph s that holds that one need to evaluate an object before it can used I used in an exchange. but since that is not the law , therefore that Rambam decided to go with the “I might have said (hypothesis that was rejected) at least in the way the Gemara understands the mishna acceding to Rav Nachman. To make this clear let me bring the Mishna and Gemara. The Mishna says anything that is made money, once one acquires one, the other acquires the other, This I might have thought refer to coin. But we know and coin cannot be use in an exchange, r Juda answered it means what is used in an exchange has to be evaluated. The Gemara then asks why was the “I would have said” a viable possibility in the first place? Answer: It would have meant coin can be used in an exchange and also fruit can be used in an exchange. But Rav Nachman held fruit cannot in an exchange, so the Gemara concludes the meaning is that if one sells an ox for 1000 after that the seller finds out that the buyer has a cow worth that same price the seller can say give me the cow instead of cash and just by saying this the acquisition is complete.---------------------------------------I wondering why the רמב’’ם decide a law like the " I would have said” instead of the conclusion of the גמרא in קידושין דף. The answer I think is that the conclusion of the גמרא is going like רב יוסף that holds that one need to evaluate an object before it can used in חליפים. But since that is not the law, therefore that רמב’’ם decided to go with the הווה אמינא (hypothesis that was rejected) at least in the way the גמרא understands the משנה according to רב נחמן. To make this clear let me bring the משנה and גמרא. The משנה says anything that is made money, once one acquires one, the other acquires the other, This I might have thought refer to coin. But we know coin cannot be use in an exchange, רב יהודה answered it means what is used in an exchange has to be evaluated. The גמרא then asks why was the הווה אמינא a viable possibility in the first place? Answer: It would have meant coin can be used in an exchange and also fruit can be used in an exchange. But רב נחמןheld fruit cannot in an exchange, so the גמרא concludes the meaning is that if one sells an ox for אלף שקלים after that the seller finds out that the buyer has a cow worth that same price the seller can say give me the cow instead of cash and just by saying this the acquisition is complete.