In The Ego and the Id Sigmund Freud drew together ideas initiated in earlier works and presented a more formalized conceptualization of the psyche or mind as an energy system taking the form of a confluence of interacting forces which may and often do, conflict. The id is the instinctual, hereditary part of the psyche. In developing this concept, Freud extended the idea of the unconscious to include not only that which is repressed but also the biological basis of personality. Although the ego is the executive of the psyche and the id 'has no will of its own', Freud clearly accorded primacy to the id, seeing it as the source of all energy and as expressing the 'true purpose of the individual organism's life'. For Freud the manifest goals of overt behaviour were false guides to the underlying instincts, since experience works through the ego to suppress or disguise their natural expression, in accordance with social constraints.