[San 5a: We begin on the last line of 4b.]
The rabbis taught (in a b'raita): Monetary cases are judged by (a court of) three. But if the judge is a recognized expert, he may even judge alone.
Rav Nachman said: Someone like me can judge monetary cases alone. And so did R. Hiyya say: Someone like me can jusge monetary cases alone.
They (their students) asked: "Like me" who has studied and who can logically analyze, and who has permission from the Exilarch, but one who has not obtained permission cannot [and his judgement is invalid]? Or perhaps one who has not obtained permission of the Exilarch [can still judge alone and)his judgement is valid?
[The Exilarch was recognized by the temporal authorities as the head of the Babylonian Jewish community. He was politically powerful as well as wealthy, and claimed direct descent from King David; in that sense, his status was almost royal.]
[The gemara answers:] Come learn: Mar Zutra the son of Rav Nachman ruled erroneously in a monetary case. He came before Rav Yosef [to ask whether he was obliged to pay for the error]. He (Rav Yosef) said: If they (the litigants) accepted you, you do not have to pay, but if not [Rashi: if they had not agreed to relieve you of liability for an erroneous judgment], you must pay. This implies that the decisions of a judge who is not authorized by the Exilarch are still binding judgments.
[The decision of an unauthorized judge is still binding, even though the judge is liable for erroneous rulings. If the decision was not binding, the winning litigant, rather than the judge, would have to make the payment.]
Rav said: One who want to judge (alone) but does not want to be liable for errors should get permission from the Exilarch. And so said Shmuel: Let him get authorization from the Exilarch.
[Rav and Shmuel both said that a judge serving with the permission of the Exilarch was exempt from liability if he made an error in judgment. The Babylonian Jewish community was led by the Exilarch {Resh Galuta, literally, the Head of the Diaspora}; the Palestinian Jewish community was led by the Patriarch {Nasi, or Leader -- President in modern Hebrew}.]
It is clear that from here to here is effective [i.e., a judge in Babylonia {here} can adjudicate in Babylonia {here}], and from there to there is effective [i.e., a judge authorized in Palestine can adjudicate in Palestine]. And it is clear from here to there [i.e., that a judge authorized in Babylonia can adjudicate in Palestine]. For here [the Exilarch] is called a scepter, and there [the Patriarch] is called a legislator. As we learned in a b'raita: "The scepter shall not depart from Judah" (Gen 49:10) refers to the Babylonian Exilarchs who rule over Israel with a scepter. "Nor the ruler's staff from between his feet" refers to the descendants of Hillel who teach Torah in public.
[JPS translates "m'hokek" as "ruler's staff, but the term is etymologically closer to "hok" -- a law, so that m'hokek becomes "legislator." Rashi simply translates the word as "a lower-status ruler."]
But what about from there to here? [Can a judge authorized by the Patriarch adjudicate in Babylonia?]
Come learn a b'raita: Rabbah bar Hana adjudicated a case [in Babylonia] and erred. He went to R. Hiyya [in Palestine]. He [R. Hiyya] said to him: If they accepted you [as a authoritative judge] you do not have to pay, but if not, then go pay. Now, Rabbah bar Hana had been authorized [by the Patriarch, but nevertheless could have been liable for errors made in judgment.] From this we learn that from here to there is not effective [i.e., that Palestinian authorization is not effective in Babylonia].
It isn't effective?! But when Rabbah bar Rav Huna argued with scholars in the home of the Exilarch, he said "I did not obtain authorization from you, but from my father, my master; and my father, my master [was authorized] by Rav and R. Hiyya, and R. Hiyya from Rabbi [who was the Patriarch]. [In short, Rabbah bar Rav Huna argued that he was not subordinate to or dependent upon the Exilarch.]
[The gemara answers:] He stopped them with mere words [i.e., he may have said that, but he was, in fact, subordinate and dependent on the Exilarch.]
But if it [authorization by the Patriarch] was not effective, what was it good for? For villages near the border [i.e., authorization by the Patriarch _was_ effective for villages near the border with Palestine.]
What was the authorization? When Rabbah bar Hana was going to Babylonia, R. Hiyya said to Rabbi [the Patriarch]: "My brother's son is going to Babylonia; may he decide [matters of ritual law such as kashrut]?" [Rabbi answered: "He may decide." [R. Hiyya:] "May he adjudicate [monetary cases]?" [Rabbi:] "He may adjudicate." [R. Hiyya:] "May he permit firstborn?" [Rabbi:] He may permit."
[Firstborn domestic animals must be given to a Kohen for Temple sacrifice. But if a judge ruled that it had a permanent blemish, the Kohen could eat it. By the time of Rabbi, there were no longer any Temple sacrifices, the firstborn would be allowed to pasture until a permanent blemish developed, after which it could be eaten.]
When Rav was going to Babylonia, R. Hiyya said to Rabbi [the Patriarch]: "My sister's son is going to Babylonia; may he decide [matters of ritual law such as kashrut]?" [Rabbi answered: "He may decide." [R. Hiyya:] "May he adjudicate [monetary cases]?" [Rabbi:] "He may adjudicate." [R. Hiyya:] "May he permit firstborn?" [Rabbi:] He may not permit."
[Firstborn domestic animals must be given to a Kohen for Temple sacrifice. But if a judge ruled that it had a permanent blemish, the Kohen could eat it. By the time of Rabbi, there were no longer any Temple sacrifices, the firstborn would be allowed to pasture until a permanent blemish developed, after which it could be eaten.]
Why did he (R. Hiyya) refer to one master [Rabbah bar Hanna] as "my brother's son" and the other [Rav] as "my sister's son?" And if you will say that these were the facts, didn't a Master say that Aivo [Rav's father], Hanna, Shela, Marta, and R. Hiyya were all the children of Abba bar Aha Karsala of Kafrei [i.e., that both Rabbah and Rav were sons of R. Hiyya's brothers]?
Rav was the son of the brother as well as the son of the sister; Rabbah bar Hanna was the son of the brother, but not of the sister.
[Imrei Binah, cited by the Artscroll edition: Abba bar Aha Karsala was a widower with a son, Aivo. Abba married a widow with a daughter; R. Hiyya was their son. Aivo married R. Hiyya's half-sister, and Rav was their son. Thus, Rav was the son of R. Hiyya's half-brother as well as of his half-sister.]
Alternatively, [R. Hiyya called Rav is sister's son] because of his wisdom, as it says (Prov 7:4) "Say unto wisdom, thou art my sister."