Do we need theory to study disease? Lessons from cancer research and their implications for mental illness.

This article applies general ideas from contemporary philosophy of science--chief among them that much good science proceeds without theories and laws--to the science of medicine. I claim that traditional philosophical debates over the nature of disease make demands on medicine that are mistaken. I demonstrate this philosophical error by applying the perspective of the philosophy of science to understanding the nature of disease in two concrete cases, cancer and depression. I first argue that cancer research produces various kinds of piecemeal causal explanation and does so without any well-developed theory of normal and malignant functioning, despite the rhetoric of some leading cancer researchers. I then defuse doubts about the scientific status of psychiatry, by demonstrating that it is not necessary to have a theory of normal functioning in order to understand and treat depression.