Psychological Medicine

Original Articles

What kinds of things are psychiatric disorders?

K. S. Kendlera1 c1, P. Zachara2 and C. Cravera3

a1 Virginia Institute for Psychiatric and Behavioral Genetics, Department of Psychiatry and Department of Human and Molecular Genetics, Virginia Commonwealth University, Richmond, VA, USA

a2 Department of Psychology, Auburn University, Montgomery, AL, USA

a3 Philosophy-Neuroscience-Psychology Program, Washington University in St Louis, St Louis, MO, USA


This essay explores four answers to the question ‘What kinds of things are psychiatric disorders?’ Essentialist kinds are classes whose members share an essence from which their defining features arise. Although elegant and appropriate for some physical (e.g. atomic elements) and medical (e.g. Mendelian disorders) phenomena, this model is inappropriate for psychiatric disorders, which are multi-factorial and ‘fuzzy’. Socially constructed kinds are classes whose members are defined by the cultural context in which they arise. This model excludes the importance of shared physiological mechanisms by which the same disorder could be identified across different cultures. Advocates of practical kinds put off metaphysical questions about ‘reality’ and focus on defining classes that are useful. Practical kinds models for psychiatric disorders, implicit in the DSM nosologies, do not require that diagnoses be grounded in shared causal processes. If psychiatry seeks to tie disorders to etiology and underlying mechanisms, a model first proposed for biological species, mechanistic property cluster (MPC) kinds, can provide a useful framework. MPC kinds are defined not in terms of essences but in terms of complex, mutually reinforcing networks of causal mechanisms. We argue that psychiatric disorders are objectively grounded features of the causal structure of the mind/brain. MPC kinds are fuzzy sets defined by mechanisms at multiple levels that act and interact to produce the key features of the kind. Like species, psychiatric disorders are populations with central paradigmatic and more marginal members. The MPC view is the best current answer to ‘What kinds of things are psychiatric disorders?’

(Received April 30 2010)

(Revised August 10 2010)

(Accepted August 15 2010)

(Online publication September 22 2010)


c1 Address for correspondence: K. S. Kendler, M.D., Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University Medical School, PO Box 980126, Richmond, VA 23298-0126, USA. (Email: