Born in Wiesbaden (Germany), son of a Christian mother and a Jewish doctor. He studied zoology and biology at the Universities of Heidelberg and Berlin. In 1914 he moved to Göttingen to study with Edmund Husserl's phenomenology. Between 1920 and 1933 he teaches at the University of Cologne. At this time, crucial to his intellectual development, publishes The unit senses. A esthesiology Guidelines (1923), preamble of his most important works: The stages of organic and man. Introduction to philosophical anthropology (1928). In 1933 he is forced to leave Germany and, with the help of Buitendijk, established in 1934 in Groningen (Netherlands). Refugee during the German occupation, his Jewishness means preserve him from sharing the fate of many Dutch Jews. In 1946 he was appointed professor of philosophy at the University of Groningen. During his years of exile Dutch written two major books: The fate of the German spirit at the end of the bourgeois era (1935) and The laughter and tears (1941). He retired in 1962, fixed his residence near Zurich, whose University he taught courses and seminars. In 1972 he was awarded an honorary degree by the same university and, thereafter, by Groningen, Freiburg and Göttingen.