Erich Fromm, Ph.D. (Sociology, University of Heidelberg, 1922), was a psychoanalyst and social philosopher who explored the interaction between psychology and society, and held various professorships in psychology in the U.S. and Mexico in the mid-20th century. Fromm's theory is a rather unique blend of Freud and Marx. Freud, of course, emphasized the unconscious, biological drives, repression, and so on. In other words, Freud postulated that our characters were determined by biology. Marx, on the other hand, saw people as determined by their society, and most especially by their economic systems.