All of us are intrinsically mad

What is madness? A defence secretary failing to guard the border between his private and public life. A society borrowing more than it can repay. A quiet Dutch engineer one day murdering his innocent neighbour. Darian Leader does not cite these examples, but he might have. He is a humanising therapist who believes that everyone has it in them to take leave of their senses — given the wrong triggers. Otherwise, for the majority, their underlying psychoses are able to rub along peacefully with their surface appearance of sanity. In short: we are all intrinsically mad, but not all of us know it, or show it.

Leader has few good words to say about modern mainstream psychiatry. This is a system in which "the individual has vanished". The psychotic subject has become an object to be treated, not a person to be listened to.

Abetted by the PR wings of the pharmaceutical industry, drugs that once were viewed as chemical restraints for eye-catching symptoms are promoted as precision cures. Leader disputes the efficacy of these drugs: "Up to two thirds" have been shown not to work.

Although Leader has written the book with other therapists in mind, his insights could have radical consequences for the way we regard madness. Once we realise that people can be mad and live normal lives, we may be able to understand what has allowed them to remain stable — and help those whose madness has been triggered. Leader squeezes fresh juice out of old cases, such as that of Daniel Schreber. In 1903, this distinguished German judge published a remarkable memoir that intrigued Freud into developing his theory of paranoia. At the time he lost his mind, Schreber was president of the Supreme Court of Saxony. Six weeks after taking office, he started sleeping badly and swallowed some sodium bromide. Days later, he was admitted into an asylum near Dresden, convinced that he was a pregnant woman charged with begetting a new race.

Actually, Leader says, Schreber's case is remarkably common. Look closer and you will see the tell-tale signs of a troubled mind battling to repair itself. Delusion offers the promise of meaning. Absence of doubt — "a clear indication of the presence of paranoia" — offers clarity. The creation of a new belief structure offers a stabilising bridge out of the experience of collapse.

What triggers psychosis will be different in each person — another good reason why every case must be treated individually and not braided into some catch-all theory. Leader is particularly convincing in his examination of Harold Shipman, the quiet physician from Hyde who killed 250 of his patients. Leader ascribes Shipman's behaviour to a childhood scene in which he watched a doctor administer a fatal dose of morphine to his mother: He decided to become a doctor, "and the agony of her death condemned him to repeat this scene again and again with his victims". Leader makes his own case elegantly and articulately for creating a safe space in which his patients might live. He is alert to the operation of "the inadvertent" in his treatment, which can only come about by listening. One day he left a session to answer the door and receive the post. His patient heard him say "Hello, postman" and explained to him, years later, "that this had been the most important moment in her therapy". Her world had become more stable by hearing an object named. By giving another name to madness, his book suggests, we can create a path back to normal life. "Normal life is simply a diversity of solutions to make the real bearable for us."

What is Madness?By Darian Leader, Hamish Hamilton, 368 pages, £20.