Cometh the hour cometh the book. I had a bit of a Jungian experience with The Divided Self. I'd been working on a play in which the main character is schizophrenic and was trawling my bookcases for drama as I like to read a lot of plays when I'm writing. I took out a chunk of Methuen plays with their distinctive blue spines, and among them was The Divided Self. I'd never heard of it and didn't know what it was doing in my bookcase. I read the back cover: 'Dr Laing's first purpose is to make madness and the process of going mad comprehensible.' Serendipity of the highest order.

What a delight when I discovered Laing was Glaswegian and the case studies, which proved invaluable, were also Glaswegians. So was my main character. I expected it to focus on clinical psychiatry and be so removed from the human experience of mental illness as to be little use to a writer. But Laing takes an existential approach which is bolstered by actual case studies of patients estranged from themselves and from society. And although requiring intellectual effort at times, this book resonates with humanity. I found it rewarding well beyond the scope of the play I was writing and learned a lot about myself, imagination and humanity.

It came as some relief to me that the schizophrenic I had created, based on a friend of mine, was, by Laing's standards, pretty accurate. But accuracy isn't authenticity. I used this book to create such authenticity of character that I went beyond what might have been possible without it. I found the explanatory chapters interesting enough but the case studies engulfed me.

I even, at times, began to fear for my own sanity, such was the incisiveness of the prose. One night lying in bed, when my wife was asleep, I held my hand in the air and tried to disassociate from it (such disassociation is one of the early symptoms of schizophrenia). I stared and stared at my hand. When I eventually managed to disassociate I got such a rush of fear coupled with an insight into the schizophrenic's dread. All in all I have been enriched as a human being and had my artistic horizons expanded. I am still writing that play and as I search my character's soul for its deepest and most exalted possibilities, this book, for me, is something of a compass.

Further reading: Self and Others (1961) explores the relationship between past experience and current behaviour; Knots (1970) is Laing’s deceptively simple guide to the ins and outs of human relationships.

View the complete list of the 100 Best Scottish Books.