Aside from the case of modeh be-miktzat that we learned about on yesterday’s daf, the only other time that a person will be required by the Torah to take an oath in court is the case of ed ehad – when a single witness steps forward to say that one person owes money to another. Ordinarily, Jewish law requires two witnesses to establish facts in court; with regard to money matters, although one witness will not be able to create an obligation to pay, he is believed to the extent that the defendant will be required to swear that he does not owe anything.
The Mishna (87a) discusses a case where a woman claims that her ketuba was not yet paid, and a single witness comes to court and says that the ketuba had been paid in full. In such a case the woman can only collect if she takes an oath that she has not yet been paid.
Despite the apparent similarity to the case where the Torah requires that an oath be taken – a point made by Rami ban Hama – as we learned on yesterday’s daf, Rava argues that a biblical oath is used to free the defendant from payment, while in our case the oath is being used to secure payment from the husband. Rava argues that the oath in our case is not biblically mandated, it is a rabbinic enactment whose purpose is to reassure the husband that he is not being cheated.
What practical difference is there between a biblically mandated oath and a rabbinic one?
According to Rashi a biblical oath is taken invoking God’s name while holding a Sefer Torah or another holy object (like tefillin). Many rishonim disagree with Rashi and rule that all oaths that are taken in Jewish courts – whether from the Torah or established by the Sages – will have those requirements. Several other differences are suggested. One example is how to treat a person who chooses not to swear. When the oath is mandated by the Torah, if someone refuses to swear, they will lose the case. When the oath is only Rabbinic, however, it is possible that the court would choose to accept the fact that the wife is holding the ketuba as evidence that it was not paid, and obligate the husband to pay, even without her oath.