How did Franz Rosenzweig criticize Martin Buber's treatment of the I-It relationship?

After reading Martin Buber’s seminal work Ich und Du (I and Thou), his friend and fellow philosopher Franz Rosenzweig offered a concise critique of Buber’s framework. Rosenzweig remarked, "Buber gives more recognition to the 'Thou' than anybody before him, but he wrongs the 'It'."1

In Buber’s philosophy, the I–It relationship characterizes interactions where beings are treated as objects of thought, tools, or conveniences, such as in scientific pursuits or certain social structures. While Buber acknowledged that the I–It relation is necessary for human survival and the creation of science, he emphasized the I–Thou relation as the ideal, direct, and mutual encounter between beings. Rosenzweig’s critique suggested that by prioritizing the "Thou" so heavily, Buber failed to grant sufficient legitimacy or value to the "It" aspect of human experience.1

Buber later defended his position by explaining that he lived in an era where the "Thou" was withering, necessitating a focus on its importance, whereas he would have praised the "It" had he lived in a time when the "Thou" was flourishing.1