  The exemplar lets us identify robust processes (Sterelny 2003, 131–2, 207–8) that are repeatable or systematic in various ways, rather than the actual processes that occur as a disorder unfolds in one person. But we do not stop there: the ultimate goal is causal understanding of a disease. We build a model to serve this end. It aims to represent the pathogenic process that accounts for the observed phenomena in the exemplar. To explain an actual history in a patient is to show how the processes unfolding in the patient resemble those that are assumed to occur in the exemplar. Exemplars provide an idealized form of the disorder that aims to identify the factors that remain constant despite all the individual variation. Not every part of a model will apply to a given patient. Once we understand the resemblance relations that exist between parts of the model and the exemplar, we can try to manipulate the model so as to change or forestall selected outcomes in the real world.