Sartre argued that freedom was inherent in the very structure of human consciousness. To be conscious is to be free. Consciousness has no prior cause but is a spontaneous upsurge. Consciousness is nothing in itself, because it is always aware of something other than itself. Consciousness is freedom. Thus, consciousness is not a thing in itself. Sartre called consciousness the “for-itself,” or pour-soi, and everything else is the “in-itself,” or en-soi. At first glance, his division of the human cosmos into for-itself and in-itself resembles René Descartes’ (1596–1650) doctrine of mental and physical substance, but Sartre went beyond Descartes’ idea of the “mental substance.”

For Sartre, as his hero in Nausea (1938) discovers in the course of a research project, even a person’s past meritorious acts or traits of character have the status of ensoi. It is a form of bad faith, for example, to pretend that one is determined to fulfill his or her duty because that is how he or she was raised, or that one’s laziness makes disciplined work impossible. People are responsible for allowing their own background, weaknesses, or strengths to be motives for action in the immediate present.