 Naturalism and constructivism have been distinguished for analytic purposes in this essay but they are not always easy to tell apart in practice. The difficulty comes from the fact that there is widespread agreement that our thinking about disease pays attention to both human values and biological phenomena, and it is not always easy to tell how a theorist explains the interactions of these factors, nor whether a given analysis is descriptive or prescriptive. For naturalists the relevant biological processes are departures from good human functioning, construed in one of several ways about which controversy rages, but to be determined by the relevant science. These biological problems result in what we judge to be difficulties in living, which may or may not be partly constitutive of disease, just as positive qualities may or may not be partly constitutive of health. For a constructivist, it is the problems people face in their lives that take priority. Their biological underpinnings are ones we count as abnormal because we have judged them to be both relevant to the conditions we disvalue and also the subject matter of a specific, medical, class of interventions, therapies and other practices. The obstacle to a successful development of naturalism is the problem of establishing a satisfactory, science-based, distinction between normal and abnormal human functioning. Overcoming this difficulty will require a closer engagement by theorists of disease with the relevant debates in the philosophy of biology.