Etiology (/iːtiˈɒlədʒi/; alternatively aetiology or ætiology) is the study of causation, or origination. The word is derived from the Greek αἰτιολογία, aitiologia, "giving a reason for" (αἰτία, aitia, "cause"; and -λογία, ). The word is most commonly used in medical and philosophical theories, where it is used to refer to the study of why things occur, or even the reasons behind the way that things act, and is used in philosophy, physics, psychology, government, geography, spatial analysis, medicine, theology, and biology in reference to the causes of various phenomena.
An etiological myth is a myth intended to explain a name or create a mythic history for a place or family, an origin story.
In medicine, etiology refers to the many factors coming together to cause an illness. It is normally the focus of epidemiological studies. The etiology of scurvy is a good example. With scurvy, sailors going to sea often lacked fresh vegetables. Without knowing the precise cause, Captain James Cook suspected scurvy was caused by the lack of vegetables in the diet. Based on his suspicion, he forced his crew to eat sauerkraut, a cabbage preparation, every day, and based upon the positive outcomes, he inferred that it prevented scurvy, without being able to say precisely how it might have worked. It was only about two centuries later, in 1926, that it was discovered that it was the lack of vitamin C in a sailor's diet that was the basic cause of scurvy. From modern knowledge we can see that the sauerkraut was probably much less effective than Cook supposed (see scurvy in the 18th century).