Id, ego and super-ego  The id, ego, and super-ego are the three distinct, interacting agents in the psychic apparatus defined in Sigmund Freud's structural model of the psyche. The three agents are theoretical constructs that describe the activities and interactions of the mental life of a person. In the ego psychology model of the psyche, the id is the set of uncoordinated instinctual desires; the super-ego plays the critical and moralizing role; and the ego is the organized, realistic agent that mediates, between the instinctual desires of the id and the critical super-ego; Freud explained that:  The functional importance of the ego is manifested in the fact that, normally, control over the approaches to motility devolves upon it. Thus, in its relation to the id, [the ego] 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. The analogy may be carried a little further. Often, a rider, if he is not to be parted from his horse, is obliged to guide [the horse] where it wants to go; so, in the same way, the ego is in the habit of transforming the id's will into action, as if it were its own. Although the structural model of the psyche refers to a mental apparatus, the id, the ego, and the super-ego are purely psychological concepts, and do not correspond to (somatic) structures of the brain, such as the kind dealt with by neuroscience. The existence of the super-ego is observable in how people can view themselves as guilty and bad, shameful and weak, and feel compelled to do certain things. In "The Ego and the Id" (1923), Freud presents "the general character of harshness and cruelty exhibited by the [ego] ideal — its dictatorial "Thou shalt"; thus, in the psychology of the ego, Freud hypothesized different levels of ego ideal or superego development with greater ideals:   The earlier in the child's development, the greater the estimate of parental power; thus, when the child is in rivalry with the parental imago, the child then feels the dictatorial "Thou shalt", which is the manifest power that the imago represents on four levels: (i) the auto-erotic, (ii) the narcissistic, (iii) the anal, and (iv) the phallic.