This is an engaging book which I read with considerable - dare I say, obsessive? - enjoyment. Lennard Davis has compiled a thorough history of "obsession" throughout the ages and across disciplines. He is particularly interested in how our society distinguishes hobbies, artistic pursuits and other excessive behaviours from obsessions, and why the medical profession pathologises behaviour that appears, at worst, benign and is, at best, responsible for some of humanity's greatest achievements. The book is laced with rich examples exemplifying obsessional people and their work.

I am an academic who has been researching and treating obsessive-compulsive disorder (OCD) for 12 years. Davis might argue that I have an obsessive interest in OCD, so am little different from the people I purport to treat, and that the shifting sands of the social-political context that informs our understanding of obsessionality is poor ground for my work.

What and who decide that my pursuits are constructive whereas those of people with OCD are problematic? Why isn't the suffering I have experienced in pursuit of my goals formally acknowledged, like that of people diagnosed with OCD?

These are excellent questions, and, in seeking answers, Davis deftly identifies holes in the diagnostic system used to define obsession. For example, he notes problems of symptom overlap that preclude solid biological explanations of OCD. He documents instances in which conceptualisations of obsessionality may have been informed more by self-interest than science. Davis also suggests that the single-minded pursuit of an activity such as writing and the need to touch pieces of furniture in a ritualistic way are both obsessions.

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Davis provides examples of famous authors and other notable people who experienced both; the implication is that if we treat their OCD, we will rob the world of their genius.

Meanwhile, our society is rife with ritualistic, compulsive acts. He concludes that obsessionality is the norm and suffering is, to an important degree, the result of being treated as an exception.

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I wonder what Davis would conclude if he referenced the literature on obsessions from psychology more broadly, particularly that which applies learning principles to understanding OCD. This literature distinguishes between behaviour motivated by reward (such as writing and science) and behaviour whose aim is to avoid punishment (such as furniture tapping).

In the former case, the overall goal is to achieve something positive, although people may suffer along the way. In the latter, behaviour is enacted to escape punishment, which is the distress arising from erroneous beliefs about the consequences of not doing it. While failing to write when one has an important idea may be problematic, failing to tap a piece of furniture is not; indeed, extinguishing that behaviour is likely to enhance the efficiency and ease of writing.

Similarly, common "obsessive" behaviours, such as handwashing, are viewed in the psychology literature as symptomatic only if fear over not doing them is out of proportion with the potential for harm - and the person feels no choice but to perform them regardless of other demands. Washing one's hands frequently during an epidemic is adaptive behaviour; washing one's hands many times beyond what is necessary, at the expense of other chores, is not.

The operationalisation of human behaviour is a vexing task. Davis reminds us that how we do this will be largely influenced by the cultural context in which that behaviour occurs. This, in its own turn, is grounded in the history of the behaviour, which is an immensely valuable observation.

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