AETIOLOGY, or ETIOLOGY (from Gr. atria, cause, and Xo yia, discourse)  , strictly, the science or philosophy of causation, but generally used to denote the part of any special science (and especially of that of medicine and disease) which investigates the causes and origin of its phenomena . An aetiological myth is one which is regarded as having been invented ex post facto to explain some fact, name or coincidence, the true account or origin of which has been forgotten . Such myths were often based on grotesque philological analogies, according to which an existing connexion between two personalities (cities, &c.) was traced back to a common mythical origin .