Do you view Torah laws the way you view state law? Personally, I only keep state law when it works out for me, but if it doesn’t work out for me, why should I care about it? After all, there is no reward and punishment and no all-seeing eye.
According to what you’re saying, it comes out that one is obligated to obey state law no matter what. I don’t understand how this should be understood.

Do you see a connection between the general question of authority and the laws of local custom? One could say that local custom is an application of the same principle in a more limited framework. If so, this might have implications for the question whether a local custom to rule in accordance with a certain opinion is also binding, and not only a custom of adding a safeguard, or regarding the ability of the local people to retract a custom, and so on. (I assume that since we’re talking about a limited group, there is no need to discuss the binding force of an erroneous custom.)

Aharon, I didn’t understand the question. Does the fact that you don’t observe it prove anything? There are also people who do not observe the laws of Jewish law. Beyond that, if the obligation depends on acceptance, then it depends on what exactly was accepted and what it is that people accepted.

A, I didn’t understand the question. What does this have to do with local custom?

Nachmanides, who is mentioned in the book Beit Yishai, uses the same reasoning for the authority of the Sages and for the force of local custom. That is, with customs too he sees it as “a law accepted by the public to which one belongs.” In light of that, the comparison between the two in various areas seems called for. It is commonly accepted among the medieval authorities to explain that an erroneous custom (against Jewish law) is not binding. Would that be different when the entire Jewish people practice that way? I mean to ask from the standpoint of logic, not from the consensus among the medieval authorities, because otherwise it becomes a paradox. Likewise, one could wonder about the ability of the people of a place to retract a custom, or about a custom that is not a safeguard but rather a ruling in a dispute. (Here I am arguing from the other direction: since the law regarding local customs is unclear, perhaps we can resolve it from the law regarding the public as a whole.)

A custom is not a law that was accepted, but a practice. There is a difference between what people do and what was legislated. One can understand that there is an obligation for a similar reason in both cases, but not with the same force.
A custom has lower force than Jewish law, and therefore a custom that goes against Jewish law is in principle void. If there is a decision here to cancel that particular law, then there is room for it.
I didn’t understand the end.

When you speak about a decision to cancel a law, do you mean a decision by the people of a place?
At the end I meant to ask whether the people of a place can cancel a custom that existed there in the past. From the Talmud it would seem not to be so (the people of Beishan, though there are different interpretations of that), but if at the level of the public as a whole such a possibility exists, why should it be different for the custom of a particular place? I also asked whether the force of local custom can also be lenient (assuming of course they have no authority to cancel Jewish law), for example to rule in accordance with a lenient opinion.

In the formation of a custom there is a built-in paradox. It begins as a deviation from what is accepted, and once it takes root it gains force and people are obligated to adopt it. The cancellation of the custom should work the same way. It starts from below, and then takes root and becomes a binding custom.
A customary mode of ruling can be lenient or stringent.

In your opinion, are there Jewish laws for which a broad enough consensus has developed after the sealing of the Talmud for them to become binding? For example, regarding carrying on the Sabbath. There are substantial difficulties with the opinion that in our cities there is no public domain on a Torah level, yet in practice there is almost complete consensus relying on the eruv. Does that have force in your view?

That consensus is not relevant. The fact that everyone thinks X does not mean that I too am supposed to think X. There is a difference between a decision to rule X and the fact that many people think X. This is more similar to custom. It is a customary mode of ruling, and it does not bind someone who has a position of his own.

How is this different from the way the Talmud was accepted? Just as the Talmud was accepted after the strengthening of the Babylonian settlement, when through a gradual process Jews around the world relied on the practices of the Geonim of Babylonia, so too here the Jews of the world rely on the medieval authorities who require six hundred thousand. Many people do not even consider how plausible the claim is, but rely on the medieval authorities who said it.

Not correct. The Talmud was accepted as a binding text. That is an act of legislation.

According to this, are the laws in the Talmud also not rabbinic, at least according to Maimonides’ approach in the first root?

Indeed, if the Talmud created the law rather than transmitted it. But interpretation of the Talmud has no connection to “do not deviate,” since there they are interpreting verses. Assuming the interpretation is correct, it is Torah law.