Etiology (/iːtiˈɒlədʒi/; alternatively aetiology or ætiology) is the study of causation, or origination. The word is derived from the Greekαἰτιολογία, aitiologia, "giving a reason for" (αἰτία, aitia, "cause"; and -λογία, -logia). 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 etiological myth, or origin myth, is a myth intended to explain the origins of cult practices, natural phenomena, proper names and the like. For example, the name Delphi and its associated deity, Apollon Delphinios, are explained in the Homeric Hymn which tells of how Apollo, in the shape of a dolphin (delphis), propelled Cretans over the seas to make them his priests. While Delphi is actually related to the word delphus ("womb"), many etiological myths are similarly based on folk etymology (the term "Amazon", for example). In the Aeneid (published circa 17 BC), Virgil claims the descent of Augustus Caesar's Julian clan from the hero Aeneas through his son Ascanius, also called Iulus. The story of Prometheus' sacrifice trick at Mecone in Hesiod's Theogony relates how Prometheus tricked Zeus into choosing the bones and fat of the first sacrificial animal rather than the meat to justify why, after a sacrifice, the Greeks offered the bones wrapped in fat to the gods while keeping the meat for themselves. In Ovid's Pyramus and Thisbe, the origin of the color of mulberries is explained, as the black berries become stained red from their forbidden love.
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).