in which the unconscious thing-presentations of the primary process are bound by the secondary processes of language (word presentations), a prerequisite for their becoming available to consciousness. The System Cns – conscious thought governed by the reality principle. In his later work, notably in The Ego and the Id (1923), a second topography is introduced comprising id, ego and super-ego, which is superimposed on the first without replacing it. In this later formulation of the concept of the unconscious the id comprises a reservoir of instincts or drives, a portion of them being hereditary or innate, a portion repressed or acquired. As such, from the economic perspective, the id is the prime source of psychical energy and from the dynamic perspective it conflicts with the ego and the super-ego which, genetically speaking, are diversifications of the id. Dreams Freud believed the function of dreams is to preserve sleep by representing as fulfilled wishes that which would otherwise awaken the dreamer. In Freud's theory dreams are instigated by the daily occurrences and thoughts of everyday life. In what Freud called the "dream-work", these "secondary process" thoughts ("word presentations"), governed by the rules of language and the reality principle, become subject to the "primary process" of unconscious thought ("thing presentations") governed by the pleasure principle, wish gratification and the repressed sexual scenarios of childhood. Because of the disturbing nature of the latter and other repressed thoughts and desires which may have become linked to them, the dream-work operates a censorship function, disguising by distortion, displacement, and condensation the repressed thoughts to preserve sleep. In the clinical setting, Freud encouraged free association to the dream's manifest content, as recounted in the dream narrative, to facilitate interpretative work on its latent content – the repressed thoughts and fantasies – and also on the underlying mechanisms and structures operative in the dream-work. As Freud developed his theoretical work on dreams he went beyond his theory of dreams as wish-fulfillments to arrive at an emphasis on dreams as "nothing other than a particular form of thinking.... It is the dream-work that creates that form, and it alone is the essence of dreaming". Psychosexual development Freud's theory of psychosexual development proposes that following on from the initial polymorphous perversity of infantile sexuality, the sexual "drives" pass through the distinct developmental phases of the oral, the anal, and the phallic. Though these phases then give way to a