פירוש על בבא מציעא 8:4

המוכר שפחתו וילדה – since a Canaanite slave is acquired by money, and when he gave the money, he acquired the female [Canaanite] slave in every place that she is. And if it is not known if until she gave birth he gave the money, and the fetus us his, or after she gave birth, and the child belongs to the owners. But a cow is not acquired by money, but by pulling/drawing the object to be acquired towards oneself, and since he pulled it, it would be known if she gave birth already or not given birth, and for this [reason], it was necessary for the Mishnah to teach, “he who exchanges,” for via “Halifin”/a form of possession by handing to the purchaser an object as a symbolical substitute, since when one draws the object to be acquired towards oneself, the other person acquires in whatever place he is in, therefore it is not known whether the animal gave birth or not.

The principles learned in this mishnah are strikingly similar to those learned in mishnah two of this chapter, so it may help to look at the explanation to that mishnah as well. Basically, the mishnah teaches that when two people are both certain about a claim (and there is no corroborating evidence) they split the disputed amount. The caveat to this rule is that if there is a previous assumption of possession favoring one of the parties, the other party must prove his claim in order to win the dispute. If one party claims that he is certain and the other party that he is unsure, the one who claims certainty wins the dispute. If both are uncertain they also split the disputed amount. We will now go through the examples in this mishnah.

יחלוקו – And our Mishnah is according to Sumachos, but the Halakha is not according to him.

If one swapped a cow for a donkey, and it gave birth, So too if one sold his slave and she gave birth, [And] one (the says, “It was born before I sold her”, and the other (the says, “It was born after I bought her”, they shall divide [the value of what was born]. If this scenario a person exchanged a donkey for a cow and the cow gave birth but it is unknown when it gave birth. The one who acquired the cow will claim that the cow gave birth after the swap and therefore the calf belongs to him, and the one who gave his cow will claim that the birth was prior to the swap and therefore the young cow belongs to him. In this case, since there is no previous assumption of ownership over the young cow, the two parties split its value. The same principle is true if the seller sold a female slave and the dispute is over when she gave birth, before or after the sale.

זה אומר גדול וזה אומר קטן – The one says the monetary value of a large slave and the other one says the monetary value of a small slave. For it were an actual slave, we hold that we don’t take oaths on slaves. And furthermore, what he claimed against him, he did not admit to him and what he (i.e. the other) admitted to, he (i.e., the first) did not claim, and there was no place for an oath.

If one had two slaves, one large and the other small, or two fields, one large and the other small,[And he sold one of them], If the buyer says, “I bought the large one” and the other says, “I don’t know”, the buyer can rightly claim the large one. If the seller said, “I sold the small one” and the buyer said, “I do not know”, he may only take the small one. If one said, “It was the large one” and the other said, “It was the small one”, the seller must take an oath that it was the small one that he sold [and the buyer can only take the small one]. If one said, “I do not know”, and the other said, “I do not know”, they shall divide the value [of both slaves or fields]. In this scenario a person sold one of two slaves or fields to his friend, and the two parties are disputing whether it the larger or smaller slave or field was sold. There are four possibilities for the two claims. 1) If they buyer claims that he is certain that he bought the large one and the seller is uncertain which he sold, the buyer gets the large one. 2) If the seller claims that he is certain that he sold the small one and the buyer is uncertain, the buyer receives only the small one. 3) If they are both certain then the seller must take an oath that he sold the small one and the buyer only receives the small one. 4) If both are uncertain they split the value of both of the fields or both of the slaves.

Questions for Further Thought:
Mishnah four: In section one and section 2iii, both parties claim certainty. Nevertheless in section one they split the value and in section 2iii, the seller takes an oath and the buyer gets only the smaller field or slave. Why is the law in these two sections different? What is essentially different about the two situations?