The sixth perek of Massekhet Bava Batra continues the discussion of business transactions involving moveable objects. The case in the first Mishna involves someone who purchases seeds that turn out to be useless for planting, but can still be used for other purposes – they can be eaten.
Our Gemara brings a parallel case from Massekhet Bava Kamma (46a) where an ox was sold, and the purchaser discovers that he was sold a shor mu’ad – a goring ox that cannot be used for plowing. When he complains, the seller tells him that he sold him the animal for slaughter, so it should make no difference whether or not the animal is dangerous; the buyer claims that he bought it to work his fields and cannot use this animal.
In this case, Rav rules that the buyer can claim mekaḥ ta’ut – the entire transaction was made under a mistaken impression – and the sale can be cancelled. He bases this ruling on the fact that rov – the majority – of purchasers buy animals for field work, so the sale can be assumed to have been made with that in mind. Shmuel argues that following rov is only appropriate in cases of issur – discussions of what is ritually permitted or forbidden. In cases of mamon – money matters – we follow the principle of ha-motzi me-ḥavero alav ha-ra’ayah – the burden of proof rests upon the claimant. Thus the purchaser would need to bring proof that he only bought the animal with the intention of using it in the field.
The Rashash asks why Rav is concerned with what most people do, given that our concern is the intention of this particular purchaser, and the Gemara has already established that he buys animals for both meat and for work. He suggests that the case in the Gemara must be talking about a wholesaler who purchases both types of animals, but since most of his customers will want to buy animals for work, he prefers to buy those types of animals.