  The DSM concept of depression, on the face of it, lumps together different psychological and behavioral types in the same category. It does this because it neglects the diverse etiologies that may produce similar signs and symptoms. There is no way to answer this charge, or to arrive at a satisfactory taxonomy that mirrors that of general medicine, unless we adopt a causal foundation for nosology as suggested by psychiatrists who urge the adoption of what I have called the strong medical model. Indeed, without an account of underlying causal structure, it becomes difficult to give a principled answer to the question why some conditions should be seen as pathological to begin with. Merely saying that members of a class have certain properties does not tell us whether, let alone why, they are mentally ill. To answer that question we need some basis for making the judgment. The DSM, as we have seen, states that we have such a basis; mental disorder is an outward sign of dysfunction. But to make that argument, we need a commitment to finding dysfunction somewhere on the basis of the outward, observable phenomena. The minimal model can only answer questions about the relationship between membership in a taxon and some other variable: it will not explain why the taxon has the nature that it has, or why it should be seen as a kind of disorder.