The Concept of Disease: Structure and Change

By contrasting Hippocratic and nineteenth century theories of disease, this paper describes important conceptual changes that have taken place in the history of medicine. Disease concepts are presented as causal networks that represent the relations among the symptoms, causes, and treatment of a disease. The transition to the germ theory of disease produced dramatic conceptual changes as the result of a radically new view of disease causation. An analogy between disease and fermentation was important for two of the main developers of the germ theory of disease, Pasteur and Lister. Attention to the development of germ concepts shows the need for a referential account of conceptual change to complement a representational account. Laypeople are familiar with dozens of diseases such as influenza, chicken pox, and cancer. Medical personnel acquire concepts for thousands of additional diseases, from Alzheimer's to yellow fever. What is the nature of these concepts? Examination of historical and contemporary writings on disease suggests that disease concepts can best be viewed as causal networks that represent relations among the symptoms, causes, and treatment of a disease. Conceptual change concerning disease is primarily driven by changes in causal theories about diseases. To defend these claims, I will review some important developments in the history of medicine and describe the major changes that have taken place in the concept of disease. I begin with the ancient Greek view of disease displayed in the writings attributed to Hippocrates, whose concepts are closely connected to the humoral theory of the causes of disease. This view dominated European medical thought until the development of the germ theory of disease, which was first hinted at in the sixteenth century but not developed and generally accepted until the nineteenth. Fracastoro, an Italian physician, wrote the first important work on contagion in 1546, but the modern germ theory of disease developed with the research of Pasteur, Lister, Koch, and others in the 1860s and 1870s. Transition from the humoral to the germ theory of disease required a major conceptual revolution, involving many kinds of conceptual change including a fundamental shift in how diseases are classified. Less radical conceptual changes occurred in the twentieth century with the discovery of genetic, nutritional, and immunological causes of disease.