In Freudian psychoanalytic theory, one of the three aspects of the human personality, along with the ego and superego .
The id is the source of instinctual impulses such as sex and aggression as well as primitive needs that exist at birth. It is entirely nonrational and functions according to the pleasure-pain principle, seeking immediate fulfillment of its impulses whenever possible. Its working processes are completely unconscious in the adult, but it supplies the energy for conscious mental life, and it plays an especially important role in modes of expression that have a nonrational element, such as the making of art. The primary methods for unmasking its content, according to Sigmund Freud , are dream analysis and free association.