Freud built the book on his own dreams — drawing material from a personal crisis following his father-in-law's death, from long sessions with his patients, and from his own self-analysis after his father's death in 1896. He had written to his close friend Wilhelm Fliess that 'this is going to be the most important work of my life' — and the prediction held.

The central thesis is this: dreams are not random brain noise but the disguised fulfilment of desires repressed by the conscious mind — most often desires reaching back to childhood. Between 'manifest content' (the surface story of the dream) and 'latent content' (the underlying wish) operates the 'dream work' (Traumarbeit): condensation, displacement, symbolic representation. Dream analysis is the technique of reversing this transformation; the dream is 'the royal road to the unconscious.'

As a conceptual revolution the book enters philosophy as deeply as it enters psychology. Since Descartes the rationalist tradition had assumed that the subject is transparent to its own thoughts — in *cogito ergo sum* I know that I am thinking. Freud removes this ground: the conscious subject sees only a small portion of its own drive structure; the rest lives on in repressed, transformed, symbolised forms. The thoughts we believe to be 'ours' have often, in fact, been thought by something other than us.

The first edition was 600 copies and took eight years to sell out. Academic psychology at first rejected the book — the method seemed 'non-scientific,' the evidence autobiographical, the conclusions too large. But the twentieth century could not bypass it: Surrealism (Breton, Dalí), Critical Theory (the Frankfurt School), existentialism (Sartre, Lacan), post-structuralism (Foucault, Deleuze), and feminist philosophy were all forced to pass through Freud's conceptual field. The clinical validity of psychoanalysis remains widely contested today, but the basic conceptual instruments of modern thought (the unconscious, repression, defence mechanism, the Oedipal relation) have become part of general culture.