What does it take to be a brain disorder?

In this paper, I address the question whether mental disorders should be understood to be brain disorders and what conditions need to be met for a disorder to be rightly described as a brain disorder. I defend the view that mental disorders are autonomous and that a condition can be a mental disorder without at the same time being a brain disorder. I then show the consequences of this view. The most important of these is that brain differences underlying mental disorders derive their status as disordered from the fact that they realize mental dysfunction and are therefore non-autonomous or dependent on the level of the mental. I defend this view of brain disorders against the objection that only conditions whose pathological character can be identified independently of the mental level of description count as brain disorders. The understanding of brain disorders I propose requires a certain amount of conceptual revision and is at odds with approaches which take the notion of brain disorder to be fundamental or look to neuroscience to provide us with a purely physiological understanding of mental illness. It also entails a pluralistic understanding of psychiatric illness, according to which a condition can be both a mental disorder and a brain disorder.