Minds are indivisible, whereas bodies are infinitely divisible. The "I" of the "I think, therefore I am" is the mind and can exist without being extended, so that it can in principle survive the death of the body. Descartes thought that mind and body interact. According to Freud, mind-body duality is not consistent. Some physical and somatic processes break our consciousness and not self-evident. Since the consciousness is broken, there are some gaps, which can be filled with psychoanalysis but of course not all of them. .
The essentials of Freud's model of mind can be restated in terms of a model of consciousness. The distinction between the conscious and unconscious, as Freud uses these terms, can be reformulated in terms of the concepts object of attention and subsidiary awareness. Freud's investigations into internal conflicts such as this led him to an eventual division of the mind into three parts, three conflicting internal tendencies, id, ego and super-ego. The id, the ego and the superego function in different levels of consciousness indeed, Freud's theory of the mind hinges upon the ability of impulses or memories to float from one level to another. The id demands immediate gratification: it is ruled by the pleasure principle, demanding satisfaction now, regardless of circumstances and possible undesirable effects. The eventual understanding that immediate gratification is usually impossible comes with the formation of the ego, which is ruled by the reality principle. The ego acts as a go-between in the id's relations with reality, often suppressing the id's urges until an appropriate situation arises. This repression of inappropriate desires and urges represents the greatest strain on, and the most important function of the mind. The ego often utilizes defence mechanisms to achieve and aid this repression. Where the id may have an urge and form a picture, which satisfies this urge, the ego engages in a strategy to actually fulfil the urge.