Gemara

49b (Mishnah): Anyone Kosher to judge is Kosher to testify, but there is someone Kosher to testify who may not judge.

(R. Yochanan): Someone who is blind in one eye may testify, but he may not judge. Our Mishnah is R. Meir:

(Beraisa - R. Meir): "V'Al Pihem Yihyeh Kol Riv v'Chol Naga" equates Dinim (monetary cases) and Tzara'as. Just like the Kohen looks at Tzara'as only during the day ("uv'Yom Hera'os"), also Dinim must be judged during the day.

Also, just like a Kohen who is blind (even in one eye) cannot rule about Tzara'as (for it says "l'Chol Mar'ei Einei ha'Kohen"), a blind person cannot judge Dinim.

A blind man used to judge in R. Yochanan's neighborhood. R. Yochanan did not say anything.

Question: R. Yochanan said that the Halachah follows a Stam (anonymous) Mishnah!

Answer: R. Yochanan rules like a different Stam Mishnah:

(Mishnah): Monetary cases must be started during the day, one may finish them at night. (This Tana does not equate Dinim to Tzara'as.)

He rules like that Stam Mishnah against ours, for it is the opinion of many Chachamim. (Our Mishnah is like R. Meir.) Alternatively, that Mishnah teaches the law among other Dinim.

Bava Kama 15a (d'Vei R. Elazar): "These are the Mishpatim (monetary laws) that you will put in front of them" equates men and women for all Dinim.

Yevamos 45b: People were calling a certain man the son of a Nochris.

Rav Asi: Didn't his mother immerse after being a Nidah?!

Koheles Rabah (Sof 2:10, on verse 2:8): Shlomo had "Shidah v'Shidos, i.e. male and female judges.

Rishonim

Rosh (Shevu'os 4:2): Since women may not testify, they may not judge, based on the rule of the Mishnah. The Yerushalmi says so. The verse says that Devorah judged Yisrael. She merely taught judges. Alternatively, the parties accepted her on themselves, due to her prophecy.

Hagahos in Tur ha'Shalem (on CM 7, 30,32): Acceptance of a woman to judge helps, just like the litigants may accept relatives to be judges. Even though one may not give rulings based on prophecy, for it says "Lo va'Shamayim Hi", this is no worse than accepting a Pasul to judge them.

Tosfos (50a DH Kol): A woman may judge, like we find that Devorah judged, even though she may not testify! "Elu ha'Mishpatim..." equates men and women for all Dinim. The verse discusses litigants and judges. We expound from it that one must come for judgment in front of Yisre'elim, and not in front of Nochrim (Gitin 88b). A woman may not testify (Shevu'os 30a)! Rather, the Mishnah teaches that any man Kosher to judge is Kosher to testify. Alternatively, women are equated to men regarding litigants, but not regarding judges. Hash-m authorized Devorah to judge. (It was a Hora'as Sha'ah, i.e. a special temporary ruling due to an urgent need.) Alternatively, she did not judge. She merely taught the laws to them. The Yerushalmi disqualifies women from judging. It learns from "v'Amdu Shei ha'Anashim" and "Al Pi Shnayim Edim", or from "va'Yish'aru Shnei Anashim ba'Machaneh."

Tosfos (Shevu'os 29b DH Shevu'as): Since a woman may not testify, she may not judge. Devorah merely taught the laws to them. Alternatively, since she was a prophet, they accepted her to judge their cases. However, "these are the Mishpatim..." equates women to men for all laws, and it discusses also judges! Indeed, the verse teaches about judges, and disqualifies Nochrim and commoners, for it refers to "Elohim", i.e. expert judges. The verse also discusses litigants, and equates men and women.

Tosfos (Yevamos 45b DH Mi): Why does Tevilah from Nidah suffice for conversion? Three judges are required for conversion, since it is called Mishpat! Even according to the opinion that mid'Oraisa, one judge suffices, a woman does not normally bring a man with her to see her immerse, and a woman cannot be a judge! We can say that three judges are needed only for acceptance of the Mitzvos, but not for the Tevilah. We say that two Chachamim stand outside (47b). This is only l'Chatchilah. Some say that since all know that she immersed, it is as if they stood there. However, women immerse from Nidah at night, and we immerse converts only during the day! However, if "Mishpat" refers only to acceptance of Mitzvos, this is fine. It is only mid'Rabanan that a convert must immerse during the day.

Poskim

Shulchan Aruch (CM 7:4): A woman is Pasul to be a judge.

Levush (5): Even though the Torah equates men and women for all Dinim, a woman may not judge, for the Torah is particular that men engage in Dinim. We learn from "v'Amdu Shei ha'Anashim...", or from "va'Yish'aru Shnei Anashim ba'Machaneh." "Anashim" is extra to exclude women. It refers to the 70 judges that Moshe picked. Devorah was different, due to Shechinah. Alternatively, she merely taught judges.

SMA (10): We learn from the Pesul of women from testimony. The Levush wrote a foreign reason.

Bach (5): The Yerushalmi says that a minor may judge, even though he cannot testify. This refers to a 13 year old who did not bring two hairs. Since he looks like an adult, it is permitted. This does not apply to women.

Etz Yosef (on Koheles Rabah 2:10, DH v'Dayanos): Shlomo's female judges judged like Devorah did. Alternatively, he had male judges for men, and female judges for women.

Radal (on the Medrash): They were not truly judges. Rather, they supervised women. The Yalkut explains that perhaps the Medrash means that Shlomo compiled laws particular to men and laws particular to women.

Hagahos in Tur ha'Shalem (32): Perhaps women can be judges if the king appoints them. See the Tumim (below).

Tumim (1): Shemayah and Avtalyon were converts. How could they be judges? For monetary laws, we can say that the Sanhedrin and great Chachamim accepted them, so it was as if all of Yisrael accepted them. However, this does not help for capital cases! We must say that a king is different. Since he can kill for the sake of the country, he may appoint a Chacham to be a leader and judge even capital cases. We say that the Reish Galusa can authorize even one who is not so learned to be a judge. We can say that the king authorized Shemayah and Avtalyon. Alternatively, we can say that Shemayah and Avtalyon would withdraw from capital cases.

Pischei Teshuvah (5): The Birkei Yosef (12) says that even though a woman may not judge, a Chachamah (learned woman) may give rulings. This is clear from Tosfos 50a, according to the answer that Devorah taught laws. Sefer ha'Chinuch (83) says that a woman cannot be a judge, yet in Mitzvah 152 he says that the Isur to give rulings when drunk applies also to a Chachamah qualified to give rulings. See Sha'arei Teshuvah (below).

Sha'arei Teshuvah (461:17): Beis Yakov brings from a Talmid of Moreinu Heshel that when there was a question of a bubble in a Matzah, he would call his household rule about it. I.e. he would ask them if they can see it from both sides, but he would rule. He relied on their perception and understanding. Women normally bake, and they know better to distinguish between bubbles due to the fire and bubbles due to Chimutz. Often, when there is a question about a defect in an interior organ of a bird or a bone without meat, Rabanan ask women, who engage in this and are experts about chickens. We rely on them, but not for Hora'ah. We find that b'Ribi was not expert about chickens (Chulin 57a).

Chasam Sofer (49b DH Kol): A slave cannot testify. The Rambam says that it is because he is not called "Achiv" regarding Mitzvos. Tosfos (Bava Kama 88a DH Yehei) explained why we cannot learn from the Gezeirah Shavah to a woman. (The Gezeirah Shavah is only stringent, to obligate slaves in Mitzvos that apply to women.) If so, why can't a slave judge? Tosfos said that a convert can judge only other converts, for he is not "amidst your brothers." If so, if a slave could judge, he could judge only slaves, e.g. regarding money that his master has no rights to it. However, slaves cannot testify, and slaves cannot accept testimony of Yisre'elim, since we do not apply "that you will put in front of them." However, Rashi says that converts can judge even Yisre'elim. If so, a slave should be able to judge slaves! Rather, judging is a Mitzvas Aseh sheha'Zeman Gerama. Even according to the opinion that b'Di'eved it is Kosher at night, unlike Tosfos (Yevamos 104a DH Mar), our Mishnah is like R. Meir, who learns from Tzara'as. Surely he disqualifies even b'Di'eved. Even according to the opinion that women may do Semichah (or other Mitzvas Aseh sheha'Zeman Gerama from which they are exempt), if she wants to be stringent on herself and judge, she cannot force a litigant to accept her for a judge, since she is not commanded.

Chasam Sofer: If Rebbi wanted to rule like R. Meir here, this Mishnah would be stronger, since it is amidst clearcut Halachah. However, that was not Rebbi's intent. He merely wanted to make a general rule 'whoever is Kosher for this, is Kosher for this, but...' However, why didn't Rebbi make his rule (like the Halachah, and) according to Rabanan? Anyone Kosher to testify is Kosher to judge, but there is someone Kosher to judge, i.e. a slave, or a woman according to one answer in Tosfos, who cannot testify! Rather, even Rabanan, who do not learn from Dinim from Tzara'as, and disqualify Dinim that began at night from "b'Yom", disqualify even b'Di'eved. Therefore, women and slaves are Pasul, for judging is Zeman Gerama.