lakewhut: Neither the Rabbinical College of America nor the Eitz Chaim Yeshiva, the two institutions that merged in 1915 to form the Rabbi Isaac Elchanan Theological Seminary, were breakaways from JTS. Rather, RIETS emerged and developed along its own trajectory.
The Jewish Theological Seminary had been Orthodox from its founding in 1886 until Solomon Schechter took over as the second President of JTS in 1902, ending the era of Hakham Sabato Morais zt”l and Rabbi Henry Pereira Mendes zt”l. Until Saul Lieberman’s death in 1983, all the professors at JTS were expected to be fully observant. The Seminary’s traditional minyan with separate seating was home to all the members of the Talmud faculty, including Drs. Israel Francus and Dov Zlotnick. When not davening at the Gerrer Shtiebel on the Upper West Side, Professor A. J. Heschel davened at the JTS traditional minyan.
To make matters even more interesting, there were graduates or former students of RIETS that ended up at the Seminary, such as Rabbi Isaac Klein and להבדיל Mordecai Kaplan יש”ו. Likewise, there were JTS graduates who became גאָר פֿרום and became part of the Orthodox milieu, such as Rabbi Herbert S. Goldstein. Goldstein was founder of the West Side Institutional Synagogue, chair of the homiletics department at RIETS, as well as president of the Union of Orthodox Jewish Congregations of America.
Rabbi Louis Bernstein, rabbi of the Young Israel of Windsor Park in Queens, professor of Jewish History at Yeshiva College, and president of Religious Zionists of America, wrote about the failed plan to establish a joint בית דין comprising rabbinic scholars from both YU and JTS, which might have kept the Conservative Movement within the bounds of normative Halachic practice. The effort was foredoomed to failure, however, as Rav Moshe זצ”ל and others nullified the קידושין of all JTS ordinees.
Interestingly, Rabbi Bernard Louis (Dov Aryeh) Levinthal zt”l, a Kovno native and Talmudist who used to travel by train to Manhattan once a week to deliver a פלפול at RIETS while serving as chief Orthodox rabbi of Philadelphia, signed a קול קורא against JTS that was published in the Yiddish press. His son was Israel H. Leventhal, founding rabbi of the Brooklyn Jewish Center (Conservative). Another signatory of the קול קורא was Rabbi Simon Finkelstein zt”l, also a native of Kovno and Talmudist who authored many ספרים. Finkelstein’s son was Dr. Louis Finkelstein, professor of Talmud at JTS as well as chancellor, and rabbi of Kehillath Israel, an Orthodox shul in the Bronx.