Madness is deep-rooted in the human imagination. The mad are unreachable, unfathomable, alarmingly other. They unsettle us. Yet we also romanticise madness. Great poetry and art spring from transcendent states at the edge of sanity, don’t they? And falling in love is a kind of madness, a stumbling into a dream world of irrationality and delusion. The lunatic, the lover and the poet are of imagination all compact. One line of thought is that madness is the price Homo sapiens has paid for the jewel of human consciousness. Perhaps it is.

There have always been alienated individuals marked out as ‘mad’ by the rest of society on account of their bizarre beliefs and eccentric behaviour, but it was not until the late 19th century that Emil Kraepelin established a formal taxonomy of signs and symptoms. Trawling the wards of Germany’s mental asylums, he concluded that there were two distinct forms of madness: manic-depressive psychosis and dementia praecox, the latter incorporating many of the clinical features we now associate with schizophrenia, such as paranoia and disordered thinking. The term ‘schizophrenia’ (‘split mind’) was coined a few years after Kraepelin had reached his conclusions by the Swiss psychiatrist Eugen Bleuler. The word captured his reformulation of dementia praecox as a splitting of cognitive and emotional functions, but it also encouraged the enduring misconception that the condition consisted of having a ‘split personality’. At any rate, madness now had a clinical profile. Between them, Kraepelin and Bleuler had set the terms of psychiatric debate for the next century and beyond.

Schizophrenia has been called the heartland of modern psychiatry because the quest to understand and treat it has come almost to define the discipline. Hence the title of Nathan Filer’s absorbing collection of case histories and essays. Filer is an award-winning novelist (The Shock of the Fall, published in 2013, also examines schizophrenia) and, as a former psychiatric nurse, he has served on the front line of mental health care. He recalls the first time he forcibly medicated a person against their will, hands trembling as he administered the injection, four colleagues holding the man down. ‘In that moment,’ he reflects, ‘I was knowingly participating in his suffering.’ He is aware from his experiences that mental health care is full of complications, ethical and political as well as clinical. What Kraepelin and Bleuler could not have anticipated was that the future heartland of psychiatry would turn out to be ‘the bloody battleground upon which the fiercest ideological disputes about madness and its meanings are fought’. Filer, like a seasoned war reporter, surveys the scene.

The battleground lies on a deep ideological fault line dividing those who regard psychological disorder as primarily the concern of biomedical science and those – mostly outside the psychiatric profession – who don’t. Freudian psychoanalytic theories held sway in the prewar period. They located the causes of mental illness in the patient’s life history, especially their childhood experiences. But diagnoses were idiosyncratic and unreliable, and the therapies on offer were ineffectual. Then, in the 1950s, with the discovery of new drug treatments and the beginnings of a more systematic approach to classification and diagnosis, psychiatry seemed at last to be finding its feet and took a biomedical turn. By the time the third edition of the American Psychiatric Association’s Diagnostic and Statistical Manual was published in 1980, with its highly specific diagnostic criteria and abandonment of psychoanalytic lingo, psychiatry had nailed its colours to the mast and had come to see itself as a truly medical, science-based discipline. Mental disorders would ultimately be reducible to physical disease processes, and the signs and symptoms of schizophrenia would be traceable to aberrations of brain function. Meanwhile, others continued to follow a more psychological path. The lack of evidence to this day of any definitive brain pathology in cases of schizophrenia and the absence of any reliable biomarkers have reinforced the case for wider social and psychological explanations. Perhaps, even, the diagnosis of schizophrenia has outlived its usefulness and should be abandoned altogether.

Alternating discussion of the key clinical and theoretical debates with vivid and at times deeply moving case studies, Filer does a brilliant job of bringing order and humanity to a seemingly chaotic scene. The Heartland begins with a survey of the politically charged language of madness – ‘patient’, ‘service user’ or ‘survivor’? – and goes on to examine issues of stigma and discrimination, the science and politics of diagnosis and treatment, and the state of play regarding progress towards an understanding of underlying causes (not very far advanced, as it happens). Other experts chip in informatively and sometimes revealingly along the way. We make it up as we go along, concedes one eminent diagnostician with a twinkle in his eye. Filer, to his credit, remains open-minded, without particular allegiance to either of the warring camps in the tiresome conflict between psychology and biological psychiatry.

The case histories are beautifully narrated. One of them involves a journalist named Erica, who planned to drink a mug of bleach. She was convinced that everyone she passed on the street knew exactly what she was intending to do and was pleased about it: Thank God she’s finally going to die. There’s also James, a soldier, who is convinced that his confinement on a locked ward is part of a secret mission. Most affecting, for this reader anyway, is the story of a mother losing her son, first through the disintegration of his mind – ‘The last flickers of her child disappeared, never to return’ – and ultimately through his death. Removing them from the abstractions of psychopathology and the interdisciplinary warfare of health professionals, drawing out their stories in respectful conversation, Filer makes these troubled people reachable, fathomable. If, to varying degrees, they remain ‘other’, they are not alarmingly so. He hopes that his book will become ‘part of the conversation’ about mental illness. It surely deserves to be.