http://en.wikipedia.org/wiki/Id,_ego,_and_super-ego
Id, ego, and super-ego are the three parts of the psychic apparatus defined in Sigmund Freud's structural 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 organised realistic part of the psyche is the "ego," and the critical and moralising function the "super-ego." [1]
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.
The concepts themselves arose at a late stage in the development of Freud's thought: the structural model was first discussed in his 1920 essay "Beyond the Pleasure Principle" and was formalised and elaborated upon three years later in his "The Ego and the Id." Freud's proposal was influenced by the ambiguity of the term "unconscious" and its many conflicting uses.
The terms "id," "ego," and "super-ego" are not Freud's own but are latinisations originating from his translator James Strachey. Freud himself wrote of "das Es," "das Ich," and "das Über-Ich"—respectively, "the It," "the I," and the "Over-I" (or "Upper-I"); thus to the German reader, Freud's original terms are more or less self-explanatory. The term "das Es" was borrowed from Georg Groddeck, a German physician to whose unconventional ideas Freud was much attracted.[2] (Groddeck's translators render the term in English as 'the It').
I think the most interesting part of Freud's theory is:
The ego is the mediator between the id and the super-ego, trying to ensure that the needs of both the id and the super-ego are satisfied. It is said to operate on a reality principle, meaning it deals with the id and the super-ego; allowing them to express their desires, drives and morals in realistic and socially appropriate ways. It is said that the ego stands for reason and caution, developing with age. Sigmund Freud had used an analogy which likened the ego to a rider and a horse; the ego being the rider while the id being the horse. The horse provides the energy and the means of obtaining the energy and information needed, while the rider ultimately controls the direction it wants to go. However, due to unfavorable conditions, sometimes the horse makes its own decisions over the rocky terrain.
When the ego is personified, it is like a slave to three harsh masters: the id, the super-ego and the external world. It has to do its best to suit all three, thus is constantly feeling hemmed by the danger of causing discontent on two other sides. It is said, however, that the ego seems to be more loyal to the id, preferring to gloss over the finer details of reality to minimise conflicts while pretending to have a regard for reality. But the super-ego is constantly watching every one of the ego's moves and punishes it with feelings of guilt, anxiety, and inferiority. To overcome this the ego employs defense mechanisms.The defense mechanisms are not done so directly or consciously. They lessen the tension by covering up our impulses that are threatening.
