Some of the material in this chapter is more difficult than that in others and the whole chapter could be omitted at a first reading. I have concentrated on writers who were immediately and directly influential on the thinking of the most important founders of the modernist movement: Nietzsche, Freud, Heidegger and Sartre. It is however of interest to look at the earlier development of the ideas of unconscious motives and of investigations of human nature through consciousness.