Levinas writes that Rosenzweig is too often present in his work to be cited. This cryptic suggestion is unfolded into an in-depth confrontation. Both philosophers implement the same speculative gesture. Rosenzweig writes in post-Hegelian times; Levinas's thinking is enriched by phenomenology and marked by the Holocaust. Their critical exploration of the relationship to the infinite offers radically new perspectives on the language, the time and the other. The confrontation raises serious questions. How is a concept of alterity possible without accepting an identuty? What are the concealed presuppositions? The questions lead to a critical analysis that cautiously explores the boundaries of dialogical thinking. But it is also the expression of the esteem held for the strong power of inspiration. As such, this book is both a critique and a tribute to Roseznweig and Levinas. The book contains an exhaustive bibliography of the comparartive studies. The manuscript was gold awarded by the Teylers fellowship of Haarlem (The Netherlands).