In historical perspective the book presents some logical concepts underlying medical thinking--definition, diagnosis, classification, semeiology, the ontology of disease, causation, scientific method, so-called "scientific medicine" and kindred topics. Histories of concrete diseases especially tuberculosis, illustrate these concepts "in action" over several centuries, within their contemporary intellectual environment. The thought modes of the earlier physicians, absurd as they may seem today, often showed excellent logic. Historically, medical thinking remains surprisingly constant, despite spectacular scientific "progress".