He returned to Dropsie College in Philadelphia, Pennsylvania, first as professor of Hebrew language and literature and chairman of the department (1957–1966); then as professor of medieval Jewish history and Hebrew literature (1966–1968). Subsequently, he moved first to University of Denver as professor of Hebraic studies, (1968–1971), then returned to New York in order to edit a Jewish encyclopedia. Eventually he took a position at Cornell University as professor of Judaic studies and chairman of the department of Semitic languages and literature, from 1971–1975.