Which beis din can declare items Hefker?

Question

There is a rule that Hefker Beis Din Hefker, that a court can declare items ownerless.

1. What are the requirements for a Beis Din to declare items ownerless?
2. Are there any courts nowadays with such powers, and if not, when was the last time there was such a court?
3. If there are no such courts, does that mean that we can't institute Takanos which will result in a loss of money to one party? For example, as many follow those opinions that there is no such thing as copyright, is it impossible to make a cherem against copying other's music illegaly (not as a chumra, but as a takana)? If one can, why has no one implemented a takana similar to the law here of retroactively mafkiya kiddushin and biya where there is a problem of aguna (let's say where the husband disappeared). This was (to the best of my knowledge) never implemented even when the Vaad Arba Artzos was around and even in the time of the Rishonim. Does this mean that there were no Beis Dins with the power to take money out even then?

Answer 1

Encyclopedia Talmudit discusses this question, at the entry "הפקר בית דין," section ד.

Some Rishonim state,¹ based on the gemara Gittin 36b, that hefker beis din can only be done with a beis din of the caliber of that of רב אמי and רב אסי, and hence it cannot be done today.

Others posit that the comparison to רב אמי ורב אסי is not literal, but is really meant to be taken in the sense of "the biggest beis din of the generation,"² or whichever beis din in town that has the ability to be מוציא ממון, to enforce the payment of money.³

There is also an opinion out there that any בית דין is capable of hefker beis din⁴, and when the gemara mentioned רב אמי ורב אסי, that was just to exclude a beis din of הדיוטות, common people (i.e., without semicha).

However, there is an opinion that even a בית דין של הדיוטות has the power of hefker beis din, in line with the supposed statement by Rav Schachter.⁵

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¹ רבינו תם in ספר הישר, siman 270; רא"ש גיטין, perek ד number 13; בית יוסף CM 67; מרדכי גיטין perek ד number 381; and more.

² רבינו תם in ספר הישר, ibid.; תוספות to Gittin 36b; רא"ש and מרדכי, ibid.; סמ"ג, Negative Commandments 271; סמ"ק siman 258; and more.

³ ספר הישר and ראבי"ה.

⁴ שלחן ערוך.

⁵ ריטב"א Gittin 36b; שו"ת רדב"ז, and רדב"ז על הרמב"ם.