Regarding the disagreement between Rabbi Yohanan ben Nuri and the hakhamim (see 45a-b), Rabbi Ya’akov bar Idi quotes Rabbi Yehoshua ben Levi as saying that we follow Rabbi Yohanan ben Nuri. Rabbi Zeira asks whether this ruling is based on a tradition about this particular case, or if it is based on the general principle taught by Rabbi Yehoshua ben Levi that we follow the more lenient position when dealing with questions about eiruv. Rabbi Yaakov bar Idi responds that he had a specific tradition in this case.
This exchange leads the Gemara to bring a series of principles about how halakha is decided in cases of disagreements. For example,
in a disagreement between Rabbi Akiva and a peer, we follow Rabbi Akiva
in a disagreement between Rabbi Yose and Rabbi Meir, we follow Rabbi Yose
in a disagreement between Rabbi Meir and Rabbi Yehuda, we follow Rabbi Yehuda
The rules that establish final verdicts based on the person who authored the position are the product of extensive research and review done by the Sages themselves. Generally speaking, such a ruling indicates that a particular basic concept or principle is the foundation for each tanna’s rulings, so following that specific tanna means that we have accepted his principle as the halakha. Nevertheless, these rules are limited in a number of ways. The Gemara states clearly that if one of the amoraim pronounces a decision that stands in contradiction with one of the general rules of pesak, we accept the amora’s decision. In other words, these rules apply only when no other decision has been handed down. Oftentimes, even if there is no clear decision but the discussion of the Gemara seems to favor one opinion over another, that opinion may be the one accepted as the halakha. Moreover, some say that these rules only apply to areas of halakha that are currently applicable, but regarding other subjects – like rulings about the Temple, etc. – these rules are not accepted at all. Finally, we occasionally find general rules that apply to a given case (e.g. we follow the lenient opinion regarding the rules of eiruv, or we follow the lenient opinion regarding the rules of mourning) that contradict the rule to follow a specific Sage.