Marc B. Shapiro was Harvard professor Isadore Twersky‘s last major student.
In his fifth lecture on R. Chaim Ozer Grodzinksi for Torah in Motion, history professor Marc B. Shapiro says: If you went to Rabbi Isadore Twersky’s shul on Shabbos when he was wearing his long kaputta (black coat), you would see a Hasidic rebbe. On the other hand, if you were with him during the week like I was, you would see a rationalist. A Brisker. Which was he? His whole life was lived as a rationalist, as a Maimonidean. On his death bed, he said that if he had to do it over again, he’d be a rosh yeshiva.
“I met with him almost every day for five years and the Isadore Twersky I knew was very much a rationalist. How this works with being a Hasidic rebbe on Shabbos? I don’t know.”
“Professor Twersky could’ve been a leader of Orthodoxy in America. People confused him with Abraham Twersky. They didn’t know who he was. He was content to stay in his area (medieval Jewry). He could’ve been a scholar in residence at shuls. He could’ve written article like Rav [Aharon] Lichtenstein, putting forth his vision of Torah and modernity.”
“I didn’t go to Isadore Twersky’s shul except on rare occasions. I found it very hard to talk to him about Maimonidean stuff and then see him on Shabbos in a different mode. I didn’t know what to call him on Shabbos. During the week, I called him Professor Twersky.”
“Twersky got annoyed with me. He said I had a chip on my shoulder about the Hasidim. He said it bothered him that I was such a mitnaged. He thought I was prejudiced on behalf of the Vilna Gaon and against the Hasidim.”
