Rafael Ambríz González

The main focus of this thesis is the project of biological psychiatry to classify psychiatric conditions, such as schizophrenia and depression, on the basis of biological features—as opposed to psychological and behavioural features, which constitute the basis for their current classification. Written as a collection of independent papers, this thesis mainly deals with three issues related to said project. The first issue is the following: classifying medical conditions on the basis of biology requires individual conditions to be defined in terms of a biological factor—asthma is, for instance, defined in terms of inflammation of the airways. The standard view is that individual psychiatric conditions are to be defined in terms of their (hypothesised) “single, clear” biological causes. However, critics of biological psychiatry rely on current evidence to point out these conditions are caused, instead, by a variety of biological, psychological, and social factors. This causal heterogeneity is thought by critics to preclude the development of psychiatric definitions based on biology. I argue (roughly speaking) that biological definitions could be achieved for those conditions notwithstanding causal heterogeneity. The second issue is the following: biological psychiatry’s search for biological definitions has been deemed to be biologically reductionist. Biological reductionism, however, is nowadays standardly refused. Hence, if the search for psychiatric biological definitions is committed to reductionism, it could be construed as a search for a prima facie defective understanding of psychiatric illness, namely, a biologically reductionist understanding which is nowadays standardly rejected. Also, if the search in question is committed to reductionism, then this search is subject to criticisms that have been advanced against reductionism. Nevertheless, I will argue that the quest for psychiatric biological definitions does not involve a commitment to reductionism, and thus it does not prompt a biologically reductionist understanding in psychiatry. Consequently, complaints against reductionism do not apply to said quest. Finally, the third issue is the following: critics remark that the above quest allows the possibility that psychiatric conditions are given purely biological definitions. These are definitions according to which a patient has the relevant condition if and only they have certain biological features—regardless of whether they have symptoms or not. Hence, purely biological definitions allow the existence of asymptomatic cases of the condition in question, and of symptomatic patients who do not to have the condition. Critics believe that if psychiatric conditions were given purely biological definitions, those definitions would not pick out the very same conditions that are currently defined in terms of symptoms. I argue, to the contrary, that those definitions would, in fact, pick out the conditions that are currently defined in terms of symptoms. Two complementary issues will also be addressed. One of them concerns how to best understand current medical classification; the other concerns what exactly distinguishes biological from non-biological approaches to psychiatric illness. If my arguments are correct, the quest of biological psychiatry for biological definitions overcomes the three difficulties mentioned above.