The clinical method practiced by physicians is always the practical expression of a theory of medicine — a theory which embraces such concepts as the nature of health and disease, the relation of mind and body, the meaning of diagnosis, the role of the physician, and the conduct of the patient-physician relationship. In recent times, medicine has not paid much attention to philosophy. When our efforts have been crowned with such great successes as they have in the past century, why be concerned if someone questions our assumptions? Indeed, we often behave as if they are not assumptions, but simply the way things are. Crookshank (1926) marks the end of the nineteenth century as the time when medicine and philosophy became completely dissociated. Physicians began to see themselves as practitioners of a science solidly based on observed facts, without a need for inquiry into how the facts are obtained and, indeed, what a fact is (Fleck, 1979). We believe ourselves to be at last freed from metaphysics, while at the same time maintaining a belief in the theory of knowledge known as physical realism.