This past Sunday, the great Harvard philosopher Hilary Putnam died at the age of 89. His philosophical legacy is difficult to summarize—he wrote on the mind, language, metaphysics, quantum physics, logic, ethics, and many other topics. He was also a mathematician, and with his collaborators he settled Hilbert’s Tenth Problem. For several months he was a Trotskyist, and he dropped out of college to recruit naval workers to the cause. In addition, Hilary Putnam was an observant Jew, a ba’al teshuvah, who turned towards religion in his middle age.Most tangibly, Putnam was a flip-flopper. This was his reputation, at least. “I have only rejected the main ideas of three of the nineteen papers in Mathematics, Matter and Method,” he wrote, in reference to his turning on his own work. In some areas of philosophy, Putnam is a leading voice on both sides of an intractable debate. He argued forcefully for a computational view of the mind; he later argued just as forcefully against it. His changes of opinion were so notorious that the satirical Philosophical Lexicon coined a unit of intellectual time in his honor, the “hilary.” (As in: “Oh, that’s what I thought three or four hilaries ago.”)It’s hard not to connect Putnam’s philosophical veering to his return to Judaism. His parents did not raise him in any faith (besides communism), and Putnam only returned to Judaism when his son asked for a bar mitzvah. He approached Rabbi Ben-Zion Gold of Harvard Hillel to discuss the possibility. The result was Putnam and his family agreeing to come to synagogue for a year preceding his son’s celebration. “Long before the year was over, the Jewish service and Jewish prayers had become an essential part of our lives,” Putnam wrote. He’d later publish a short scholarly book entitled Jewish Philosophy as a Guide to Life, examining the thought of Franz Rosenzweig, Martin Buber, and Emmanuel Levinas.When I was in college, I prayed at Harvard Hillel’s Orthodox minyan. I used to watch through the window as Putnam and his wife, Ruth Anna, arrived for services. My time in shul was often fraught, in those days. There were cracks in the foundations that had been built by my teachers in yeshiva, and I feared I was about to topple. I gravitated towards philosophy in my studies, partly because it was the subject that scared me the most.I knew of Putnam’s work from my courses, where we studied his famous Twin Earth thought experiment. I devoured his short books, Ethics Without Ontology and The Collapse of the Fact Value Dichotomy. It was only after this initial exposure that I learned about Putnam’s Judaism, and knew to keep an eye out for him on Saturday mornings. Here was one of the most respected philosophers of his era, praying under the same roof as I was, in my troubled state. That helped me, quite a bit.Did Putnam have “the answers?” I remember carefully reading his writing and interviews for some sort of path out of my own religious confusion. “There was and continues to be tension between the way I think when I ‘do philosophy’ and the way I think when I view the world religiously,” he wrote, adding “I would not want it to be otherwise.” It took me years to begin to get used to living with this tension; I still find it difficult. (John von Neumann’s line on mathematics—“you don’t understand things, you just get used to them”—seems to apply here too.)In 2014, Putnam started a blog called “Sardonic Comment.” The last posts were a continuation of a 50-year debate on the nature of language with his high school classmate, Noam Chomsky. Chomsky had felt mischaracterized by a recent post, and Putnam published Chomsky’s email in full. It ends, “Sorry that our efforts to get together have so far failed. Hope we’ll have a chance to talk about these (and many other) things one of these days.”I hope they did find that chance. Putnam’s life—and his influence on me—is a testament to the power of conversations on things that matter.