 This counterexample is instructive, however, since there are two ways of amending the proposal in the light of it. First, perhaps the principle of nondistinct sustaining causes fails to capture our intuitions about causes of disease. A second possibility is that the principle is a good causal condition, but that the account of evils is too broad, and needs to be restricted to a more intuitively medical set of evils, rather than the broader class of impediments to well-being. The section on health will go over the terrain that’s relevant for the second option; the current discussion is about the causal condition. Boorse (1975, 1976, 1977, 1997) and his followers have opted for a more restrictive view of the causes of disease. They contend that disease necessarily involves biological malfunction. Boorse distinguished “disease” from “illness”. The former is the failure to conform to the “species-typical design” of humans, and the latter is a matter of judgments that a disease is undesirable, entitles one to special treatment, or excuses bad behavior. An account of malfunction must be parasitic on a theory of function. Boorse thinks a function is a ‘species-typical’ contribution to survival and reproduction (1976, 62–63). Disease is failure to function according to a species design, in which functional efficiency is either degraded below the typical level or limited by environmental agents (1977, 550, 555, 567; 1997, 32). Boorse understands this as functioning “more than a certain distance below the population mean” (1977, 559) for the relevant set of humans. (Since not all members of a species have the same design in every respect, we need to specify reference classes according to biologically relevant subgroups.) This cutoff point, he thinks, can only be specified as a matter of convention, but this conventional element does not threaten the objectivity of diagnoses. Responses to Boorse since the original theory was formulated have concentrated on two issues. First is the apparent existence of states like tooth decay that are widespread, so apparently statistically normal, yet definitely pathologies. The second is the“line-drawing problem” Schwartz (2007) which comes in two related guises: how we are to reference classes and how we can distinguish between normal and abnormal levels of functional efficiency.