In September 1897 a Viennese neurologist of forty-one wrote to his closest friend, Wilhelm Fliess, a nose-and-throat specialist in Berlin, that he no longer believed his own theory of nervous illness. The year before, Sigmund Freud had told his colleagues that the hysterical patients he treated had all been sexually abused in early childhood, and that this buried memory was what made them ill. One of his reasons: the abuse would have had to be far more common than seemed possible. What he did next made psychoanalysis. He kept the scenes his patients had described but changed his account of them: where they had not happened, they had been imagined and wished for, and a wish could make a person ill as surely as an event. Looking back in 1925, he wrote that for a neurosis the reality inside the mind counted for more than the reality outside it. Historians still argue over how much his patients had told him, and over whether he gave up the first theory for good reasons.
He had been trained to look for causes in matter. As a medical student at the University of Vienna, where he later said he was expected to feel inferior because he was a Jew, Freud spent six years in the laboratory of the physiologist Ernst Brücke, studying the nerve cells of fish and crayfish. In 1882 Brücke, knowing he had no money, advised him to give up research for medical practice. A fellowship took him to Paris in the winter of 1885 to watch Jean-Martin Charcot, the renowned neurologist, show that hysteria was a real illness with regular laws, that men suffered from it too, and that hypnosis could produce its paralyses. Back home, Vienna's medical society received his report with disbelief. Freud turned instead to the method of his older colleague Josef Breuer, whose patient known as Anna O. had lost her symptoms by talking about them. In 1895 he drafted a psychology built from neurons and measurable quantities of energy, then left it unfinished; it was published only in 1950. From then on he described the mind in its own terms, while insisting that psychology was a natural science.
His father, Jakob, died in 1896, and over the following years Freud analysed his own dreams and childhood memories as he analysed his patients'. The result was The Interpretation of Dreams, published in November 1899 with 1900 on its title page. Its claim is the one he is remembered for: most of what moves a person happens outside awareness. Wishes that cannot be admitted, above all a child's sexual wishes towards its parents, are pushed out of consciousness — repressed — but not destroyed, and they return in disguise as dreams, slips of the tongue, jokes and neurotic symptoms. Interpretation works back from the disguise to the wish. The first printing of 600 copies took eight years to sell. In lectures given in Vienna during the First World War, Freud set psychoanalysis beside Copernicus and Darwin as a third blow to human self-love, because it denied the conscious self command of its own mind.
The theory kept changing. The First World War sent home soldiers who relived their terror night after night, which no wish could explain, and in Beyond the Pleasure Principle (1920) Freud proposed a drive towards death beside the drives of life. Three years later The Ego and the Id divided the mind into three agencies: the id, the reservoir of the drives; the ego, which faces the world; and the super-ego, the parents' authority taken inside. In 1927 The Future of an Illusion applied the same reasoning to religion, which it traced to the adult's wish for the protecting father of childhood. In 1923, the year of The Ego and the Id, doctors had found cancer in Freud's mouth; over the sixteen years left to him the surgeon Hans Pichler operated on his jaw more than two dozen times.
Whether psychoanalysis is a science is still disputed. The philosopher of science Karl Popper held that because it could explain any behaviour at all, it could never be shown to be wrong, and so lay outside science. The philosopher Adolf Grünbaum answered in 1984 that Popper was wrong and that many of its claims can be tested. Its effectiveness as a treatment is just as contested.
In 1933 the National Socialists burned his books in Germany. Freud stayed in Vienna even after Germany annexed Austria in March 1938, until the Gestapo arrested and questioned his daughter Anna, herself a psychoanalyst, on 22 March. He left Vienna on 4 June and reached London two days later. He died there on 23 September 1939, after doses of morphine ended the pain of a cancer no longer operable. His four sisters had stayed behind in Vienna; they were deported in 1942 and died at Theresienstadt and Treblinka.