Eduyos chapter 1, mishnah 5. This mishnah too reflects on the way the Mishnah itself operates, but this time not in relation to the preceding mishnayos specifically, rather as a general question.
The well known rule is "acharei rabbim lehatos" - the halachah is determined by the majority. When the Sanhedrin convenes, both sides of the dispute are heard, and in the end they "took a vote and concluded": a vote is held, and the halachah is ruled according to the opinion of the majority. Once the matter has been decided and a majority opinion has formed, that is the halachah. If so, the fundamental question arises: why did the editor of the Mishnah, Rabbi Yehudah HaNasi, choose to include in it the minority opinions as well, the opinions of individuals? Seemingly these opinions have been rejected from the halachah, so what reason is there to mention them at all?
The words of the mishnah:
"Velamah mazkirin divrei hayachid bein hamerubin, ho'il ve'ein halachah ela kedivrei hamerubin" - why should the opinion of the minority be brought in the Mishnah alongside the opinions of the majority, when the halachah is ruled like the majority, and the purpose of the Mishnah is to teach the practical halachah? What does the Mishnah seek to accomplish by mentioning opinions that are not the halachah?
Explanation:
Let us first explain the answer in our own words, and then see how it emerges from the language of the mishnah. We will call the first Sanhedrin "the authors of the Mishnah." After the Mishnah was sealed, a second Sanhedrin may arise in its own generation, and when a halachic case comes before it, its obligation is to weigh the facts, the reasoning, the sources and the tradition, and to rule accordingly. It is not necessarily bound to follow the ruling of a previous generation. It emerges that the halachah may change: the Mishnah established that a certain thing is permitted, even though there is a minority that forbids it, while the second generation of the Sanhedrin is entitled to say: we have weighed the case anew, and in our understanding the thing is forbidden - and thereby it nullifies the ruling of the Sanhedrin that preceded it.
It is worth mentioning in this context that the most common individual opinion in all of Shas is that of Rabbi Meir. The Gemara says that the halachah is not like Rabbi Meir, and the reason is that he was wiser than all of them, and his colleagues could not fathom the depth of his reasoning. Even though he was the wisest among them, they were unable to follow his logic, and therefore they followed their own logic and his opinion was rejected. But if a later generation does fathom the depth of his reasoning and understands it, that generation can rule like him.
And from here to the next question: what would the law be if a third generation arises, and the Sanhedrin of that generation wishes to nullify the ruling of the second generation and return to what was established in the Mishnah in the first place? Are they permitted to nullify the words of the second generation, even if they are not as wise as they are and do not possess as good a tradition as they do? Precisely here the role of the list of individual opinions in the Mishnah is revealed.
The mishnah continues:
"Im yir'eh beis din es divrei hayachid veyismoch alav" - if the beis din of the second generation sees fit to rule like the minority opinion mentioned in the Mishnah, and relies upon it in its ruling, then it has ruled on the basis of the individual opinion. And then - "she'ein beis din yachol levatel divrei beis din chavero ad sheyihyeh gadol mimenu bechochmah uveminyan": the third generation, a new Sanhedrin of seventy one, cannot nullify the ruling of the second generation that relied on a minority opinion, unless it is greater than it in two dimensions.
The two dimensions of greatness:
"Bechochmah" - the most widely accepted explanation is that the av beis din, the senior judge and head of the Sanhedrin, is greater in wisdom in the third generation than the one in the second generation.
"Uveminyan" - here several explanations have been offered. It certainly does not mean a greater number of judges, since their number is fixed at seventy one. Rather it refers to the number of students who support that Sanhedrin, or to the pool of Torah scholars from which the Sanhedrin is built. And some understand that it refers to the age of the av beis din. Either way, the point is that both dimensions of greatness are required together in order for the third generation to be able to nullify the words of the second generation.
This limitation applies specifically when the second court based its ruling, at the very least, on a minority opinion recorded in the Mishnah. But if its ruling does not rest on a minority opinion in the Mishnah, the third generation may overturn it, since this is the responsibility of the Sanhedrin in every generation: to rule according to its own understanding. This, then, is the Mishnah's answer to its question.
The conclusion of the Mishnah:
The Mishnah goes on to emphasize the point, so that no room for doubt remains: "gadol mimenu bechochmah velo veminyan, beminyan velo vechochmah - eino yachol levatel devarav, ad sheyihyeh gadol mimenu bechochmah uveminyan" - greater than it in wisdom but not in number, or in number but not in wisdom, cannot nullify its words, until it is greater than it in both wisdom and number. If the Sanhedrin of the third generation is greater in wisdom, meaning that its head of the court is wiser than his predecessor, but its generation does not have as many students; or if its generation has more students, but the head of the court is not as wise as the one of the second generation - it does not have the power to overturn the ruling of the second generation that relied on an individual opinion in the Mishnah, until it is greater than it in wisdom and in number together.
In summary: although the halachah is decided according to the majority, the individual opinions were recorded in the Mishnah so that they could serve as a foundation for later courts. A court may reconsider and rule according to the minority opinion, and once it has relied upon it, a later court can no longer overturn that ruling unless it is greater than it in wisdom and in number. It emerges that the individual opinion is not an opinion that was rejected and forgotten, but a pillar upon which the halachah can rest for generations.