Practicing medicine means not only applying our humanism, compassion, knowledge or skills, but also basing our actions on the fundamentals of philosophy, science, art and logic in their universal sense. Medicine is defined as ‘the art and science of diagnosis, treatment, and prevention of disease, and the maintenance of good health’. The science of medicine is organized reasoning. With the development of microbiology, biochemistry, histology, pathology, genetics and other basic sciences, the goal of medicine became a search for the true picture of a disease, the identification of real causes and a search for the best treatment. Clinical medicine has benefited from the experience of public health in epidemiology, health economics, health programs and health services evaluation. The concepts of disease, illness and sickness apply to a great variety of health problems since they have been defined on different bases during the development of medicine.