Is authority binding in error?
The Torah commands us to follow the instructions of the Sanhedrin Ha-Gadol: “do not deviate from what they tell you, neither right, nor left.” (Devarim 17:11). According to Chazal, this pasuk affirms the authority of the Sanhedrin even if they err. (Sifri 155). This is hard to swallow. Why should we follow a mistake?
To answer this question, Ramban develops a theory of psak halacha. (Peirush on Devarim 17:11). Torah is open ended. Terse verses, ambiguous passages, and apparent contradictions invite interpretation. Because of the variety of human opinions and perspectives, judgements will inevitably differ. Disputes will thus inevitably ensue.
Generally, Ramban has a high regard for differences in psak. (Peirush on Devarim 16:18 and 17:10). But, only to a degree. Diversity begets instability. A fractious society cannot last. The halacha needs a final authority to ensure unity: the Sanhedrin. While the Sanhedrin is not infallible, nor protected against scrutiny — anyone is free to object to the Sanhedrin’s reasoning — the Sanhedrin enjoys immunity from overrule. Once it paskins, no one can issue a contrary psak. Even if the Sanhedrin is mistaken. Thus, the Sanhedrin can calm the fire of factions.
Elsewhere, Ramban distinguishes between a talmid chacham ha-ra’oy li’horah (a Talmud Chacham qualified to issue a ruling) and a talmid chacham she’aino ra’oy li’horah. (Hasagos al Sefer Ha-Mitzvos no. 1.) A qualified Talmud Chacham may disagree with the Sanhedrin in his private observance of the Torah, provided he does not issue a contrary psak. An unqualified Talmud Chacham may not. We can distinguish between two types of authority the Sanhedrin enjoys: an-authority and in-authority. An-authority refers to an individual or body which is trusted to make the correct decision. In-authority refers to an individual or body which is invested with executive power and can issue directions or commands. For example, if you ask for a diagnosis from a doctor, the doctor is an-authority: we follow his diagnosis because we trust his judgement. If a general issues an order to his soldiers, the general is in-authority: we follow his command because he has executive power. For the non-qualified, the Sanhedrin is in-authority, and must be obeyed even in error. For the qualified, the Sanhedrin is an-authority, and, while obedience is not necessary, reverence for the station is necessary. Hence, only private dissent is permissible.
However, in Ramban’s view, only the Sanhedrin enjoys this special status. Because of the open-ended nature of Torah, psak depends on the opinions and perspective of the posek. The halacha is not cut and dry, applied not with scientific rigour, nor mathematical exactness. (Melcahmos HaShem, intro.). A posek’s judgement is developed through his study with his rebbeim, through immersion in the mesorah. The enterprise of psak is predicated on the mesorah.
Mesorah cultivates our opinions and perspectives, allowing us to discriminate between valid and invalid interpretations. The capacity to regard the Sanhedrin’s psak as mistaken is itself dependent on a sense of what makes one interpretation better than another. This sense is cultivated through the mesorah.
The Sanhedrin is the physical embodiment of the mesorah: only the wisest scholars with the deepest traditions comprise the court (See Iggros Ha-Grid Hilchos Sanhedrin and Rav Schachter on the Parsha (vol. 1), Yisro). Therefore, the Sanhedrin has a protected status. Their psak, even if mistaken, carries the weight and legitimacy of the whole system of halacha. The Sanhedrin represent the basis of halachic authority.
Why then do we follow the Sanhedrin even when they are mistaken? We need to have a final word to stabilize the democratic system of psak. In some sense, the decision could be arbitrary: any finality would protect against factionalization. However, we only follow the Sanhedrin in error because of their status as ba’alei mesorah.