This book is an introduction to logical structure specifically as it relates to clinical medicine. Doctors apply logic every day in clinical medicine, but most have had no formal training in the field. This book solves that problem. Symbolic logic uses symbols to create logical structure. In clinical medicine, doctors transform signs of disease are into symbols which are related to each other to describe disease activity. This gives physicians the power to conceptualize disease, design treatments for disease, and monitor disease activity. This process lays the foundation for the science of clinical medicine. Indeed, the fabric of contemporary clinical medicine is woven by the application of symbolic logic to the analysis of disease. This book explores the function of signs, what happens when signs of disease are treated as symbols, and how the creation of functional relationships between signs of disease leads to a classification of diseases. This leads to the concept of the diagnosis