Aphthous stomatitis century BC), although it seems likely that this was oral ulceration as a manifestation of some infectious disease, since they are described as occurring in epidemic-like patterns, with concurrent symptoms such as fever. Aphthous stomatitis was once thought to be a form of recurrent herpes simplex virus infection, and some clinicians still refer to the condition as "herpes" despite this cause having been disproven. The informal term "canker sore" is sometimes used, mainly in North America, either to describe this condition generally, or to refer to the individual ulcers of this condition, or mouth ulcers of any cause unrelated to
The Canon of Medicine anatomy, and physiology. The book explains the causes of health and disease. Avicenna believed that the human body cannot be restored to health unless the causes of both health and disease are determined. He defined medicine ("tibb") as follows: Avicenna begins part one by dividing theoretical medicine and medical practice. He describes what he says are the "four causes" of illness, based on Aristotelian philosophy: The material cause, the efficient cause, the formal cause, and the final cause: Avicenna's thesis on the elements of the cosmos is described by Gruner as "the foundation of the whole "Canon"". Avicenna insists here