Psychiatric classification

The biopsychosocial paradigm can be conceived as an approach to the classification of mental disorders. Practitioners require diagnostic categories that facilitate shared, reliable standards for identifying mental disorders. The biopsychosocial paradigm has clearly been influential in the production of such classificatory systems. For example, psychosocial factors were explicitly referenced in the axial system of DSM-IV under Axis IV. DSM-V no longer adopts this axial system, but still reflects the perceived importance of social, cultural and environmental factors in accurate diagnosis and classification. In the past few years the DSM has been challenged by the Research Domain Criteria (RDoC), which seeks a new taxonomy of mental disorder based on neurobiological measures. At least for now, however, the biopsychosocial-style approach to psychiatric classification remains orthodoxy.

It is important to distinguish two possible interpretations of this approach. On a conceptual interpretation, biopsychosocial factors determine the content or meaning of psychiatric categories. ‘Major depression’, for example, might be analysed as meaning ‘the condition characterised by biological, psychological and social factors X, Y, and Z’. On an epistemic interpretation, in contrast, biopsychosocial factors merely provide clinical signs or evidence for classifying a patient under a certain psychiatric category. This latter interpretation seems more appropriate in understanding the influence of the biopsychosocial paradigm on the DSM. Further philosophical development is needed, however, to clarify the commitments of the approach.

Psychiatric causation

A second conception of the biopsychosocial paradigm relates to the study of psychiatric causation. The past few decades have seen an explosion of research on the relationship between environmental ‘stressors’ or ‘insults’ and the development of mental illness. Epidemiological studies indicate that for most disorders, the risk of developing the condition is not determined by biological factors alone. There is complex interplay between causal factors at biological, psychological and social levels. To pick just one example, perceived parenting style is associated with risk of various psychopathologies in adulthood, including major depression and anxiety disorders. Gene–environment interactions and correlations present further intricacies, which are only just beginning to be understood.

In this context, the biopsychosocial paradigm can be developed via the claim that the causes of mental illness are spread over multiple explanatory levels. This sort of approach is discernible, for example, in Kendler's ^{Reference Kendler6} description of the ‘dappled’ nature of psychiatric causation, a term he borrows from Cartwright. Once again, however, this merely marks the beginning of a view; more philosophical focus is needed. What is the operative notion of causation here? How should we make sense of claims such as that socioeconomic inequality can be a cause of schizophrenia? What causal mechanisms are involved? These remain some of the most challenging conceptual questions currently facing psychiatry.

Prevention and treatment of psychiatric disorder

The foregoing biopsychosocial-style view of causation may influence the ways in which clinicians intervene to prevent or treat these psychiatric disorder. Leff and colleagues ^{Reference Leff, Kuipers, Berkowitz, Eberlein-Vries and Sturgeon7,Reference Leff, Kuipers, Berkowitz and Sturgeon8} for example, investigated the links between relapse rates of people with schizophrenia and their social environment. They found that ‘Relapse of schizophrenia is more likely if patients live with relatives who are excessively critical and/or over-involved. Such relatives are designated as high EE [expressed emotion]’. ^{Reference Leff, Kuipers, Berkowitz, Eberlein-Vries and Sturgeon7} This causal insight led Leff and colleagues to devise a programme of social interventions that significantly reduced relapse rates by reducing relatives' expressed emotion and/or reducing patients' social contact with high expressed emotion relatives. But the proposed biopsychosocial conception of prevention and treatment is not merely an extension of a ‘dappled’ view of causation: the approach raises distinctive and challenging questions regarding social policy and the ethics of healthcare interventions. What types of psychological or social intervention are permissible in the prevention of mental disorder? How should we adjudicate between pharmacological and psychosocial treatments? These philosophical issues demand closer scrutiny.

Metaphysics of psychiatric disorder

Our final conception of the biopsychosocial paradigm relates to the metaphysics of mental disorder. By way of background, the philosophical mind–body problem concerns the nature of the relationship between mental states – notably qualitative states of phenomenal consciousness – and states of the brain. Psychiatrists sometimes write as if the only two views of this relationship are reductionism and dualism, and as if a denial of reductionism is tantamount to embracing dualism. Yet the current orthodoxy in philosophy of mind is neither reductionist nor dualist, but rather non-reductive and monist. Glossing over many important details, this position maintains that descriptions and explanations expressed in the language of psychology are irreducible to descriptions and explanations expressed in the language of biology, while insisting that mental states are nonetheless entirely physical in nature.

Viewed in this context, Engel's metaphysical aspirations for the biopsychosocial paradigm seem prescient, if insufficiently articulated. The paradigm was presented as an alternative to the ‘reductionist biomedical model’, ^{Reference Engel1} and thus naturally lends itself to integration with the anti-reductionist philosophical theories of mind that have prospered since the 1960s and 1970s. Most philosophers of mind today would think it uncontroversial that accounts of mental disorder must engage psychological-level concepts. Some ‘vehicle externalists’ even view the mind as partly constituted by processes within our natural and social environments. ^{Reference Chalmers and Clark9} Although much further discussion is needed, it is natural to see these theories as embodying biopsychosocial-style views of the nature of mental disorder.

Although highly theoretical, these metaphysical issues have major practical repercussions. For example, if some aspects of mental disorder are irreducibly psychosocial, then arguably our classificatory systems should reflect this. Insights from philosophy of mind therefore may inform the conflict between biopsychosocial-style systems and the RDoC, the latter clearly reflecting an ambitiously reductive view of mental disorder. More controversially, if vehicle externalism is true, then the psychiatric sciences will have to look outside the skin for a complete understanding of mental disorder. If my reasoning capacities are partly constituted by extrinsic processes, for example, then presumably these capacities may be impaired by changes in these processes. These suggestions are promissory and in need of significant development. They serve to illustrate, however, the continued relevance of the biopsychosocial paradigm to the foundations of psychiatry.