Id, ego, and super-ego

Id, ego, and super-ego are the three parts of the "psychic apparatus" defined in Sigmund Freud'sstructural model of the psyche; they are the three theoretical constructs in terms of whose activity and interaction mental life is described. According to this model, the uncoordinated instinctual trends are the "id"; the organized realistic part of the psyche is the "ego," and the critical and moralizing function the "super-ego." 

Even though the model is "structural" and makes reference to an "apparatus", the id, ego, and super-ego are functions of the mind rather than parts of the brain and do not necessarily correspond one-to-one with actual somatic structures of the kind dealt with by neuroscience.

Id :

It is the dark, inaccessible part of our personality, what little we know of it we have learnt from our study of the dream-work and of the construction of neurotic symptoms, and most of this is of a negative character and can be described only as a contrast to the ego. We all approach the id with analogies: we call it a chaos, a cauldron full of seething excitations... It is filled with energy reaching it from the instincts, but it has no organization, produces no collective will, but only a striving to bring about the satisfaction of the instinctual needs subject to the observance of the pleasure principle.

Developmentally, the Id is anterior to the ego; i.e. the psychic apparatus begins, at birth, as an undifferentiated id, part of which then develops into a structured ego. Thus, the id:

“

contains everything that is inherited, that is present at birth, is laid down in the constitution -- above all, therefore, the instincts, which originate from the somatic organisation and which find a first psychical expression here (in the id) in forms unknown to us" EGO: “ ...The ego is that part of the id which has been modified by the direct influence of the external world ... The ego represents what may be called reason and common sense, in contrast to the id, which contains the passions ... in its relation to the id it is like a man on horseback, who has to hold in check the superior strength of the horse; with this difference, that the rider tries to do so with his own strength, while the ego uses borrowed forces  Super EGO: The Super-ego aims for perfection.It comprises that organized part of the personality structure, mainly but not entirely unconscious, that includes the individual's ego ideals, spiritual goals, and the psychic agency (commonly called 'conscience') that criticizes and prohibits his or her drives, fantasies, feelings, and actions. “ The Super-ego can be thought of as a type of conscience that punishes misbehavior with feelings of guilt. For example: having extra-marital affairs. ” The Super-ego works in contradiction to the id. The Super-ego strives to act in a socially appropriate manner, whereas the id just wants instant self-gratification. The Super-ego controls our sense of right and wrong and guilt. It helps us fit into society by getting us to act in socially acceptable ways