I recently visited long-lost haredi cousins for the first time over Shabbat. I am a newly modern Orthodox woman and at my Shabbat table, everyone joins in the zemirot. At my cousins', however, only the men are allowed to sing. Why is that?
I sympathize with your puzzlement. I am sure that the joyful singing greatly adds to your Shabbat, and to be excluded from this experience causes confusion about modern Orthodox practice and possibly insult, especially for a new member of the Orthodox community. Although I cannot resolve this situation, I am hopeful that a greater understanding of the law in question will help alleviate the tension.
In two Talmudic passages, the third-century sage Shmuel states "kol ba'isha erva," loosely translated as "a woman's voice is indecent." One of these sources (Brachot 24a) follows a Talmudic ruling that a woman's thighs and other uncovered body parts inappropriately distract a man from properly reciting the Shema prayer. Many, but not all, medieval commentators (Beit Yosef OC 75) assert that this conjunction proves that one is also forbidden to recite the Shema while listening to a woman's singing voice (kol isha in Hebrew). According to this approach, the sages prohibit kol isha because it leads to illicit or distracting thoughts.
Based on this source, one prominent liberal American Orthodox rabbi ruled that the intent of this passage was to only prohibit kol isha when it poses a potential distraction to ritual worship. This responsa, along with a Conservative historian's claim that women sang in public arenas throughout the ages, propelled Rabbi David Golinkin of the Masorti movement to rule that women can sing in the presence of men.
The overwhelming majority of Orthodox rabbis reject this claim, contending that the second source (Kiddushin 80a) of kol ba'ishah erva clearly forbids men from listening to women sing. In the course of a larger discussion regarding intermingling between the sexes, the Gemara once again cites Shmuel's statement, unrelated to Shema or other rituals. Rabbi Yosef Karo codified this prohibition in his list of other licentious behavior, such as giddy flirting (Even Ha'ezer 21:1). Independent of any additional problems it might cause, such as illicit thoughts, kol isha remains problematic because it represents, in its own right, frivolity between the sexes.
Defining kol isha as inappropriate interaction, however, opens the door for leniencies in contexts where a woman's singing cannot be deemed licentious. Rabbi Moshe Feinstein (Igrot Moshe OC 1:26), for example, ruled that there is no prohibition for girls under 12 to sing in front of men, since we are not concerned about frivolity with them. A major modern debate revolved around female performances on radio or television. Rabbi Eliezer Waldenberg (Tzitz Eliezer 5:2) contended that since there is no physical interaction, this does not constitute licentious behavior. Rabbi Ya'acov Breisch (Chelkat Ya'acov 1:163), however, ruled stringently, arguing that any pleasure from a woman's voice, even with no genuine contact, remains prohibited. Rabbi Ovadia Yosef (Yabia Omer OC 1:6) took a middle position, arguing that men can only listen to radio songs if the listener is not acquainted with the singer or has not seen her picture.
This brings us to your question about zemirot. After World War II, a French co-ed youth group asked Rabbi Yehiel Weinberg about the propriety of their participants singing zemirot together (Seridei Esh 1:77). Weinberg recalled that while women refrained from singing zemirot in his native Lithuania, leading rabbis in Germany, where he had run a yeshiva, sanctioned women to join the men at the table in song. He justified this tradition by citing scholars who contended that religious songs cannot lead to licentiousness or illicit thoughts. They proved their claim from the book of Judges, when the prophetess Deborah led the nation in hymns following a military victory. Weinberg further argued that in an age when well-educated women display tremendous self-respect, prohibiting their participation would only insult these teenagers and distance them from Judaism.
Many rabbis, particularly in the haredi world in which your cousins live, strongly reject this position. Some dispute Weinberg's legal argument, while others marginalize the ruling as an emergency measure intended exclusively for his times. Other rabbinic luminaries, including Rabbi Joseph Soloveitchik and Rabbi Haim David Halevi, permitted joint singing of zemirot, and much of the religious-Zionist community, including my family, follows this opinion.
Depending on how frustrating you find this experience, you might hesitate to return to your cousins on Shabbat. Personally, I would recommend trying again, viewing this as a very infrequent compromise made, like many others, for family gatherings. Either way, I hope that this information will increase confidence in your modern Orthodox lifestyle and propel you to continue to investigate the source of divergent halachic practice.
The writer is the on-line editor of TraditionOnline.org and teaches in Jerusalem, where he is pursuing a doctorate in Jewish philosophy at Hebrew University.