Children's literature has its roots in the stories and songs that adults told their children before publishing existed, as part of the wider oral tradition. Because of this it can be difficult to track the development of early stories. Even since widespread printing, many classic tales were originally created for adults and have been adapted for a younger audience. Although originally children's literature was often a re-writing of other forms, since the 1400s there has been much literature aimed specifically at children, often with a moral or religious message. To some extent the nature of children's fiction, and the divide between older children's and adult fiction became blurred as time went by and tales appealing to both adult and child had substantial commercial success.