Folktales form a major part of non-canonical Christian tradition. Folklorists define folktales (in contrast to "true" myths) as stories that are considered purely fictitious by their tellers and that often lack a specific setting in space or time. Christian-themed folktales have circulated widely among peasant populations. One widespread folktale genre is that of the Penitent Sinner (classified as Type 756A, B, C, in the Aarne-Thompson index of tale types); another popular group of folktales describe a clever mortal who outwits the Devil. Not all scholars accept the folkloristic convention of applying the terms "myth" and "folktale" to different categories of traditional narrative.