Enrique Simonet in the context of "Nessus (centaur)"

The natural history of disease is the course a disease takes in individual people from its pathological onset ("inception") until its resolution (either through complete recovery or eventual death). The inception of a disease is not a firmly defined concept. The natural history of a disease is sometimes said to start at the moment of exposure to causal agents. Knowledge of the natural history of disease ranks alongside causal understanding in importance for disease prevention and control. Natural history of disease is one of the major elements of descriptive epidemiology.

As an example, the cartilage of the knee, trapeziometacarpal and other joints deteriorates with age in most humans (osteoarthritis). There are no disease-modifying treatments for osteoarthritis---no way to slow, arrest, or reverse this pathophysiological process. There are only palliative/symptomatic treatments such as analgesics and exercises. In contrast, consider rheumatoid arthritis, a systemic inflammatory disease that damages articular cartilage throughout the body. There are now treatments that can modify that auto-immune inflammatory process (immune modulating drugs) that can slow the progression of the disease. Because these medications can alter the natural history of disease, they are referred to as disease-modifying antirheumatic drugs.

Thanatology is the scientific study of death and the losses brought about as a result. It investigates the mechanisms and forensic aspects of death, such as bodily changes that accompany death and the postmortem period, as well as wider psychological and social aspects related to death. It is primarily an interdisciplinary study offered as a course of study at numerous colleges and universities.

The word is derived from the Greek language. In Greek mythology, Thanatos (θάνατος: "death") is the personification of death. The English suffix -ology derives from the Greek suffix -logia (-λογια: "speaking").