He later studied philosophy in Freiburg and Heidelberg, where he came into contact with Max Weber and Georg Lukács, among others.
During World War I, he served as a nurse, and in 1921 he took his doctorate in the culture of friendship in Germany in the 19th Century.
Internationale Revue für Sozialismus und Politik», a publication that he later became editor of.
Here, he introduced young writers such as Hannah Arendt, Walter Benjamin and Herbert Marcuse.
In 1931 he contracted polio, and in 1933 he lost his job due to his Jewish background, and he emigrated with his family to the United States in 1935.