One of the central discussions in our perek is how the witnesses whose names are signed in a shtar – a contract or other legal document – can be authenticated. Our Gemara quotes Rav as distinguishing between different types of testimony, arguing that kiyyum shtarot – authenticating the signatures on a shtar – is rabbinic in nature, while Kiddush ha-hodesh – establishing the Jewish calendar based on testimony regarding the New Moon – is essential on a biblical level.
With regard to the shtar, the approach of most commentaries is that on a biblical level the signatures that appear in the document are sufficient for us to accept it as legitimate testimony, and there is no need to confirm its authenticity. If at some point we discover a forgery or error, it will be presented to the court, which will then review the case and rule based on the new information. Based on this, Rav Hai Gaon and others rule that if one of the judges on the court that was convened to authenticate the signatures turns out to be disqualified, we do not need to begin the process anew, since on a biblical level the shtar did not really need to be examined in this way.
Furthermore, the Rema in the Shulḥan Arukh (Hoshen Mishpat 41:4) rules that since the need for authentication is only Rabbinic, we do not really need a beit din; even a yahid mumheh – a single expert – would suffice in such a case.
The Rambam’s approach is exactly the opposite. He believes that on a biblical level, the signatures in the shtar are worthless, since the only testimony that is really acceptable to prove the existence of the loan, sale, etc. would be a personal statement by reliable witnesses. Nevertheless, the Sages established a process whereby the court can rely on written testimony, i.e. the signatures of the witnesses on the shtar, on the condition that those signatures are properly examined and authenticated.