Researchers attempting to explain and treat psychiatric disorders have long discussed the need for new disorder categories. A common proposal is to develop a causal classification system whereby psychiatric disorders are classified according to the causal processes that produce and sustain them. I evaluate the prospects for causal classification of psychiatric disorders. First, I motivate the need for a causal classification system of psychiatric disorders. Second, I introduce one framework for causal classification, the exemplar model. Third, I examine multiple forms of causal complexity that the exemplar model must successfully navigate if it is to be a viable classification model for psychiatry. I argue that the exemplar model can handle some issues of causal complexity but not others. I conclude that psychiatry should utilize two models of classification, the exemplar model and the network model, because each fulfills some, but not all, of the purposes of classification systems.