As we learned above (daf, or page, 38) the halakhah is that a kofer bakol – a defendant who totally denies a monetary claim made against him – is believed without being required to bring any further proof; if he is modeh be-miktzat – he denies that he owes all of the money, but admits that he owes part of it – then he must pay the amount that he admits to and then take an oath that he does not owe any more.
According to Shmuel, this ruling applies even in cases where the plaintiff demands two different things; for example, if he claimed that the defendant owed him wheat and barley and the defendant admitted only to the claim that he owed him wheat. Shmuel rules that he will have to pay the wheat that he owed and take an oath that he did not owe the barley.
In a similar case Rav Anan quotes Shmuel as teaching that if the defendant was accused of owing wheat, and he immediately admitted to owing barley we check to see whether he appeared to be doing this in a tricky manner – in order to avoid being considered a modeh be-miktzat – or if he was clarifying the truth. If we find reason to suspect him, then he will be obligated to take an oath on the part that he denies, but if he appears honest in his admission it will suffice to pay the amount that he admits to.
How do we decide if he is being honest or not?
Rashi argues that it is entirely up to the bet din. The court can decide whether he was sincere in his admission or if he will be suspected of acting in this manner in order to avoid the oath that will be imposed on him as a modeh be-miktzat. If they feel that it was the latter situation, they can impose the oath on him. The Ramban says that we need to distinguish between a case where the plaintiff completed his accusation, claiming only that the defendant owed him wheat and the defendant admitted to barley and a case where the plaintiff was in the middle of his claim and the defendant jumped in to his words to make a different admission. In the former case we trust the defendant, while in the latter case his behavior will be viewed with suspicion.