 The dominant approach in much of the recent philosophical scholarship on the philosophy of medicine views disease concepts as involving empirical judgments about human physiology (Boorse 1975, 1977, 1997; Scadding 1990; Wachbroit 1994; Thagard 1999; Ereshefsky 2009). These so-called “naturalists” (sometimes called “objectivists”, for example see Kitcher 1997, or “descriptivists”) focus on what is biologically natural and normal functioning for all human beings (or more precisely human beings who are members of relevant classes such as those within a particular age group or of the same sex). They argue that medicine should aim to discover and describe the underlying biological criteria which allow us to define various diseases. Christopher Boorse’s revised account has been the most influential in the literature, claiming that health is the absence of disease, where a disease is an internal state which either impairs normal functional ability or else a limitation on functional ability caused by the environment (Boorse 1997). “Normal functioning” is defined in terms of a reference class which is a natural class of organisms of uniform functional design (i.e., within a specific age group and sex), so that when a process or a part (such as an organ) functions in a normal way, it makes a contribution that is statistically typical to the survival and reproduction of the individual whose body contains that process or part. His definition includes specific reference to the environment so as not to rule out environmentally-induced conditions which are so common as to be statistically normal such as dental caries.