Question

[Even if someone who is insane with respect to one matter is judged insane regarding all his statements, we hold that we do not look at the speaker.]
 
Mishnah Hullin 2:4: If he slaughtered the esophagus and severed the windpipe, etc., Rabbi Yeshvav says: it is a carcass; Rabbi Akiva says: it is a tereifah. Rabbi Yeshvav stated a principle in the name of Rabbi Yehoshua: Anything that became invalid in its slaughtering is a carcass, and anything whose slaughtering was properly done but something else caused it to become invalid [for example, one of the tereifot — Bartenura] is a tereifah. And Rabbi Akiva conceded to him. Maimonides wrote in his commentary on the Mishnah: “We do not need to explain that Rabbi Yeshvav’s principle is true, since Rabbi Akiva, who had disputed it, already conceded to him.”
א. What is the meaning of this principle that if a person retracts, then his earlier opinion is as though nonexistent? After all, Rabbi Akiva earlier was presumably no less great than Rabbi Akiva later. And if before he retracted there were two against one, then after he retracted there are three (Rabbi Yeshvav, Rabbi Yehoshua, and Rabbi Akiva later) against one (Rabbi Akiva earlier). The rule that the law follows the later authorities would seemingly apply only if a new argument is added, not if they simply decide the dispute like one side (all the more so not when it is a third-party ruling). After all, there were aspects pointing in each direction: one day it seemed one way to Rabbi Akiva and the next day another way, so what of it? It seems as though a person retracting from an opinion he held is a stronger indication that there is a mistake in that opinion than if someone else merely disagrees with it, but what is the explanation for that? [And one could go further: if Abaye and Rava were switching opinions every half hour like a game of catch, there should be nothing surprising about that. Even though in practice, even among great scholars — or especially among them — retraction from one’s view is fairly rare.]
[In column 410 and in the comments you wrote that well-formed and stable positions are an indication that the person is currently grasping the truth as it is perceived by a personality like his. I didn’t exactly understand it there, but I tucked it away in the back of my mind, and someday it will become clear. Here I’m asking it from another angle.]
 
ב. By the way: in the Mishnah there are many cases where the House of Hillel retracted and ruled in accordance with the words of the House of Shammai. [I tried searching with a somewhat clumsy search site and found one other place that documents a retraction that is not House of Shammai and House of Hillel, in Taanit 4:4: “These are the words of Rabbi Akiva.” Ben Azzai said to him: “This is how Rabbi Yehoshua would teach,” etc., and Rabbi Akiva retracted and taught like Ben Azzai. But there it seems to be a matter of a tradition in the name of Rabbi Yehoshua, unlike the Mishnah in Hullin, where from the wording it seems this is only Rabbi Yehoshua’s opinion.] But this seems a little odd. If there is no significance to the fact that someone once thought differently, then they should simply state the law without the dispute. If the goal is to document facts, that’s what Thucydides is for. And if my little search gadget is reliable, and indeed only the House of Hillel and Rabbi Akiva have documented retractions, then it is interesting why דווקא them. It is known that Jewish law was decided in accordance with the House of Hillel, and the entire foundation of the Mishnah is according to Rabbi Akiva, but that still does not explain it. After all, it is not likely that out of all the tannaim only these retracted; rather, the others’ retractions were simply not recorded.