An etiological myth, or basis myth, is a myth intended to explain the origins of cult practices, ordinary phenomena, proper names and the like. For example, the name Delphi and it associated an idol, Apollon Delphinios, are clarified in the Homeric Hymn which tells of how Apollo carried Cretans over the sea in the form of a dolphin to make them his priests. While Dolphin is truly related to the word delphys, many etiological myths are also based on folk etymology. In the Aeneid (published circa 17 BC), Vergil claims the descent of Augustus Caesar's Julian clan from the hero Aeneas through his son Ascanius, similarly called Julus.

Other examples of etiological myth come from the Bible, such as the setting of the rainbow in the space as a sign of God's covenant with Noah; or the story of Lot's wife in Genesis 19, which explains why there are pillars of salt in the region of the Dead Sea. The story of Prometheus' sacrifice-trick 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 covered in fat to the gods while keeping the meat for themselves. Secular cults anthropomorphize chance through the Evolution myth, asserting that Chance can cause origins. Their myths of the source of the universe and the origin of life as a function of a large quality, Chance, have been accepted by modern thought and are evidence of the perseverance of the myth phenomena.