Should works in the philosophy of psychiatry enter the reading lists of practising psychiatrists? It is easier to make a case that such volumes should be part of psychiatric training. Beyond that, syntheses are the reasonable medium of conversation with philosophers, and the current volume is among the better ones. The conversation should be had because, whether they are called that or not, philosophical issues in the field will remain difficult for the foreseeable future. These problems touch on the definitions and habits involved in diagnosis, bringing into focus, for instance, the relation between (delusional) belief attribution and typical norms of rationality and evidence adjudication. They are also embedded in efforts of theorising mental illness, since even basic decisions – for example, what counts as satisfactory explanation – will require non-trivial justification. Finally, the commerce between surrounding culture (e.g. conspiratorial narratives) and the symptoms seen in clinical settings generates puzzles which are in part philosophical. This anthology will help with refining conceptual questions, especially those concerning nosology and explanatory language, and with having a sober representation of the abyss that these questions sometimes open.

One may place this book in the vicinity of monographs on delusion, such as those by Jennifer Radden or Lisa Bortolloti, or of other anthologies, such as the one edited by Bortolloti in 2018. Interestingly, Routledge published almost simultaneously another collective volume on philosophical accounts of delusion, edited by Falcato and Gonçalves, which is less ambitious in scope, despite some thematic and auctorial overlaps. For pedagogical uses and quick referencing, the current volume has a claim to become default. It is comprehensive, and the list of authors includes some of the more important scholars in the field.

The Handbook focuses on delusion as concept in need of clarification but also as explanandum – that is, an array of symptoms manifested across current diagnostic categories, for which a scientifically acceptable account is still needed. The short and generally clear chapters are grouped in six sections, starting with recent debates about the nature of delusion, going through the physiognomy of delusions in various maladies, the relation between delusions and evidence, or that between delusions and actions, and concluding with a wider perspective in which ethical concerns and cultural factors are added to the picture. A few themes are recurrent, and they generally emanate from ontological or epistemological concerns. An example is doxasticism (see, e.g. chapters 1, 14 and 19), which is jargon for the idea that delusions are beliefs – bizarre and pathological but beliefs nonetheless. Doxasticism matters because it is at the heart of all the definitions of delusion used in diagnosis. If doxasticism proves untenable, as some authors think (chapter 20), the language in which symptoms are described will need rethinking and consequences will ramify to candidate explanations of symptoms and to diagnostic criteria.

In the current cultural climate, even topics that may seem remote from clinical practice have renewed relevance. That bizarre conspiratorial beliefs have massive appeal is a challenge both to our conception of mental illness and to that of a well-functioning mind. Comparisons between beliefs of clinical significance and those of merely political import are unavoidable (see, e.g. chapters 37 and 38).

As psychiatry falls deeper in the gravity well of neuroscience, some of the themes in this volume will gain in importance. Transitioning from an explanatory language based on lay psychological terms (belief, fear) to neuropsychiatry is not an inconsequential task of translation. Perhaps the shock of abandoning Freudianism is the proximate comparison. Some authors in this volume (see chapters 24 and 25) argue that folk psychological notions are unsalvageable because they are incommensurate with models of delusion based on brain circuitry. This kind of problematisation will continue, I expect, to be part of what makes psychiatry sui generis in the medical universe.