In Sigmund Freud's theory of psychoanalysis, he sought to explain how the unconscious mind operates by proposing that it has a particular structure. He proposed that the self was divided into three parts: the Ego, the Superego, and the Id.

The general claim that the mind is not monolithic or homogenous continues to have an enormous influence on people outside of psychology. The mind is also the point in the body in which all of the sadistic tendencies arise.

The ancient Greeks also divided the soul into three parts of their own, with only one part in common. The Greek parts were the desiring part (which is like what Freud called the id, but without so much implication of suppressed deviant sexuality), the spirited part, and the reasoning part.

The Id:

The Id (Latin, "it" in English, "Es" in the original German) represented primary process thinking — our most primitive need gratification type thoughts. The Id, Freud stated, constitutes part of one's unconscious mind. It is organized around primitive instinctual urges of sexuality, aggression and the desire for instant gratification or release. Freud borrowed the term Id from the "Book of the Id" by Georg Groddeck, a pathfinder of psychosomatic.

The Superego:

The Superego ("Über-Ich" in the original German, roughly "over-I" or "super-I" in English) represented our conscience and counteracted the Id with a primitive and unconscious sense of morality. This primitive morality is to be distinguished from an ethical sense, which is an egoic property, since ethics requires an eligibility for deliberation on matters of fairness or justice. The Superego, Freud stated, is the moral agent that links both our conscious and unconscious minds. The Superego stands in opposition to the desires of the Id. The Superego is part of the unconscious mind, and based upon the internalization of the world view, norms and mores a child absorbs from parents and the surrounding environment at a young age. As the conscience, it is a primitive or child-based knowledge of right and wrong, maintaining taboos specific to a child's internalization of parental culture.

Freud considered the Oedipus Complex to be a formative stage in the development of the superego.

The Ego:

In Freud's view the Ego stands in between the Id and the Superego to balance our primitive needs and our moral beliefs and taboos. ("Ego" means "I" in Latin; the original German word Freud applied was "Ich".) He stated that the Ego consists of our conscious sense of self and world, a highly structured set of unconscious defenses that are central in defining both individual differences in character or personality, the symptoms and inhibitions that define the neuroses, and ultimately serving as the executive branch of the mind which leads to action. Relying on experience, a healthy Ego provides the ability to adapt to reality and interact with the outside world in a way that accommodates both Id and Superego. Freud believed the energy used to run the ego (such as to dissolve reality, moral and neurotic anxiety) was derived from the Id in the form of cathexis and from the Superego in the form of anticathexis.