From syndromes to symptoms: Advancing our understanding of mental disorders

Traditionally, psychiatric syndromes have formed the primary target of explanation in psychopathology research. However, these syndromes have been significantly criticised for their conceptual weakness and lack of validity. Ultimately, this limits our ability to create valid explanations of these categories; if the target is invalid then our explanations will suffer as a consequence. Using depression as extended example, this doctoral thesis explores the theoretical and methodological challenges associated with classifying and explaining mental disorders, and develops an alternative explanatory approach and associated methodology for advancing our understanding of mental disorders – the Phenomena Detection Method (PDM; Clack & Ward, 2020; Ward & Clack, 2019).   This theoretical thesis begins by evaluating the current approaches to defining, classifying, and explaining mental disorders like depression, and explores the methodological and theoretical challenges with building theories of them. Next, in moving forward, I argue that the explanatory target in psychopathology research should shift from arbitrary syndromes to the central symptoms and signs of mental disorders. By conceptualising the symptoms of a disorder as clinical phenomena, and by adopting epistemic model pluralism as an explanatory strategy, we can build multi-faceted explanations of the processes and factors that constitute a disorder’s core symptoms. This core theoretical and methodological work is then followed by the development of the PDM. Unique in the field of psychopathology, the PDM links different phases of the inquiry process to provide a methodology for conceptualising the symptoms of psychopathology and for constructing multi-level models of the pathological processes that comprise them. Next, I apply the PDM to the two core symptoms of depression – ¬anhedonia and depressed mood – as an illustrative example of the advantages of this approach. This includes providing a more secure relationship between the pathology of depression and its phenotypic presentation, as well as greater insight into the relationship between underlying biological and psychological processes, and behavioural dysfunction. Next, I evaluate the PDM in comparison to existing metatheoretical approaches in the field and make some suggestions for future development. Finally, I conclude with a summary of the main contributions of this thesis.   Considering the issues with current diagnostic categories, simply continuing to build explanations of syndromes is not a fruitful way forward. Rather, the complexity of mental disorders suggests we need to represent their key psychopathological phenomena or symptoms at different levels or aspects using multiple models. This thesis provides the metatheoretical and methodological foundations for this to successfully occur.