Benjamin Smart (Birmingham) gives a talk at the MCMP Colloquium (18 December, 2013) titled "On the Classification of Diseases". Abstract: Identifying the necessary and sufficient conditions for individuating and classifying diseases is a matter of great importance in the fields of law, ethics, epidemiology, and of course medicine. Here I engage in this conceptual debate to facilitate a metaphysical analysis of disease. My targets are two-fold: first, to provide a means of uniquely picking out one disease from another, and second, to provide a metaphysical ontology of diseases; that is, to give an account of what a disease is. Following existing work in the philosophy of medicine and epidemiology (primarily Boorse; Whitbeck; Broadbent), philosophy of biology (LaPorte; Hull), conditional analyses of causation (JL Mackie; Lewis), and recent literature on dispositional essentialism (Mumford 2004; Mumford and Anjum 2011; Bird 2007), I reject naturalist accounts of disease in favour of a dispositional constructivist conception of disease, whereby (i) the identification of a disease involves a large normative element (and further that as diseases are biological kinds, the distinctions we draw between them are unlikely to be ones that carve nature at the joints), (ii) that diseases are individuated by their causes, and (iii) that diseases are causal processes best seen as simultaneously acting sequences of mutually manifesting dispositions. This conception is prima facie subject to numerous counter-examples, but through employing a projectivist account of natural bodily function, I argue that the constructivist is able to avoid the naturalist objections. I go on to consider the possibility of dispositional accounts of psychological conditions, concluding that although plausible, there are fundamental ontological differences between the two.