 Following Boorse, Hausman assumes that there is an average range of performance within a normal population in normal circumstances that can tell us what physiological profile a healthy system ought to have. His reply is developed and expanded by Garson and Piccinini (2014). The issue is whether these normal circumstances can be specified without begging the question, or whether Wachbroit is correct to think of medical normality as an idealization that is unrelated to statistical normality. On any approach, a worry is that if we cite behavioral factors in establishing normality they will reflect contested conceptions of human flourishing. Distinguishing failures to flourish from functional abnormalities will always be a special problem for psychiatry. For example, judgments of irrationality are central to many psychiatric diagnoses, and our standards of rational thought reflect not biological findings but standards derived from normative reflection. The possibility of psychiatric explanation employing the methods and models of physical medicine, then, depends on how much of our psychology is like the visual system – i.e. decomposable into structures to which we can ascribe a natural function (Murphy 2006). Within medicine more generally, the prospects for a general naturalism about disease depend on our ability to understand human biology as a set of structures whose functions we can discover empirically, and our capacity to understand disease causally as the product of failures of those structures to perform their natural functions.