A Metaphysics of Psychopathology stands out as one of the best books in the philosophy of psychiatry written in recent years. Psychiatrists, psychologists, and their critics, often ask whether this or that condition – AHDH, multiple personality disorder, mild depression – is a real disorder. While such debates are common, and commonly acrimonious, few ask what is meant by terms such as ‘real’, ‘objective’, and ‘true’ in this context. Zachar illustrates how closer attention to philosophy can here be worthwhile and sets out to make sense of what it means for a disorder to be real.

The first half of Zachar's book sets out his pragmatist framework. Material specifically related to psychopathology only begins to be discussed in chapter 8. To many readers this philosophical front-loading may appear off-putting. Zachar, however, sees his approach as necessary. More than a metaphysics, his pragmatism offers a methodology, and Zachar seeks to enable readers to gradually shift how they think about conceptual issues through reading the first half of the book. In considering an abstract concept, whether it be ‘real’ or ‘depression’, Zachar urges us to think as concretely as possible. For example, we can elucidate concepts in terms of their contrasts; abstract talk of ‘reality’ is easier to keep a handle on if we specify what contrast we have in mind, ‘real’ v. ‘fake’, or ‘real’ v. ‘artificial’, for example.

When it comes to asking whether some condition is a real disorder, Zachar urges us to abandon the notion that there is any underlying real distinction that can be drawn between disorders and normality. Jerome Wakefield's popular approach, according to which disorders are harmful dysfunctions, is criticized as being little use – our knowledge of the evolutionary past is so limited, thinks Zachar, that to claim that a condition was either adaptive or maladaptive in evolutionary history is no more than hand-waving. More positively, Zachar suggests we should accept that the domain of psychiatry is an ‘imperfect community’. The psychiatric domain is centred on those disorders which were first treated by psychiatrists – extreme psychotic states that were seen in asylum patients. Over time, as psychiatry has expanded, more and more conditions have come to be considered psychiatric disorders on pragmatic grounds; other conditions can fairly be considered disorders if they seem more or less similar to more central cases of disorder, and if treatment by mental health practitioners seems worthwhile.

Chapters of the book flesh out Zachar's approach by exploring the DSM-5 debates about grief and narcissistic personality disorder. Zachar sees psychopathology as a messy domain in which symptoms cluster in complex ways. Disorder concepts are abstractions that act to group together individuals whose problems are more or less similar. Useful abstractions (which can be called ‘real disorders’ as an honorific) group patients into classes that do a good job in enabling reliable inferences to made, for example, about prognosis, or likely treatment response. In Zachar's view, more than one classificatory scheme might do a reasonably good job in enabling inferences, and the best classification will likely depend on our interests. Using such an approach, Zachar suggests that at least some grief-induced depressive episodes can fairly be considered disorders, in that it is reasonable to group them with other cases of depressive disorder and see them as requiring treatment. Similarly he holds that some cases of NPD can be considered disorders on the basis that they are similar to clearer cases of psychopathology such as psychopathy or low-functioning borderline personality disorder. Zachar's approach seeks to take the heat out of debates about the reality of disorder – rather than arguing that this or that condition really is or really is not a disorder, we can switch to considering whether the evidence suggests that putative cases can usefully be classified together, and whether treatment by mental health professionals might prove helpful.

A Metaphysics of Psychopathology is an excellent book. Anyone interested in the philosophy of psychiatry would do well to read it, and once they've read it will probably want to read it again. Zachar knows a very great deal about both philosophy and psychopathology, and has thought about the issues for a long time. While I'm not convinced that Zachar's approach is always right, he's always clear and thought-provoking.