Medicine counts as a scientific discipline. It is commonly said that in a scientific discipline knowledge and action are justified by reasoning. In the present book we are concerned, among many other things, with medical knowledge and action, and thus, with the nature, methods, and problems of reasoning in medical practice and research. To this end, we shall need theories and techniques of reasoning, i.e., logic, to analyze whether any logic is used, or may be instrumental, in medical reasoning. Since it would be unfair to leave the reader in the dark about what we understand by the term "logic", we have explained it in the present, final Part VIII by introducing some useful fruits of the science of logic, deductive and inductive ones, so that we may apply them in other parts of the book.The terms "deductive" and "inductive" will be explained later.