If two people both claim shel avotai – that a piece of land belonged to their ancestors – and in an attempt to buttress their claims, one brought witnesses that it had belonged to his ancestors, while the other brought witnesses that he had lived there for three years, and therefore had a ḥazaka (presumption of ownership), Rabba rules that we believe the one who has lived there for three years because of the principle mah lo le-shaker – what interest does he have in lying? Specifically, if he wanted to lie he could have done so in a more convincing manner, by saying that he had purchased it and had lived there for three years – a claim that would have been accepted by the courts. Abaye disagrees, arguing that witnesses are always more powerful that a claim based on mah lo le-shaker.
Can one of the parties change his claim? Specifically, can the individual who brought witnesses that he had been on the land for a significant amount of time, now claim that he did not really mean to say that the land belonged to his ancestors? Can he now argue that he really had purchased it from the other party, and what he meant when he said shel avotai was that his claim on the property was so strong – having purchased it and worked it for three years – that it is as if it had belonged to his ancestors?
This situation, referred to by the Gemara as to’en ve-ḥozer ve-to’en – to claim and rescind the claim in order to make a different one – is the subject of a disagreement between Ulla (who permits) and the Sages of Neharde’a (who would not accept the new claim). As the Rashbam points out, to’en ve-ḥozer ve-to’en will only be considered if it clarifies and explains the earlier claim. If it negates the first claim entirely, the Gemara is clear that the new claim will not be accepted even according to Ulla. The Ramah says that this is true only if witnesses come, weakening his first claim and forcing him to clarify his statement. If no witnesses came, then he would be able to change his claim as he pleases without penalty. The Rashba limits this right only to cases where he wants to change from one winning claim to another. If he first admitted that he was wrong, however, and then wants to change to a winning claim, the court will not accept his new argument.