The purpose of a fable is to illustrate a basic moral ideal to a reader in a memorable and interesting way. Alternately, a myth can have multiple purposes, ranging from an explanation of an observation or a reason behind a moral ideal or a demonstration or critique of a historical event. Myths often are more elaborate, covering a wider range of topics and typically contain a didactic quality or specific purpose beyond the obvious telling of a story that requires some textual analysis by the reader to understand.
The character in a fable are either animals with the ability to think and speak in human ways or children. Within the fable, they are confronted with a challenge that they confront with means at their disposal. As an example, the popular fable of the turtle racing the rabbit, where the turtle wins because he is determined and consistent, uses two animal characters. Myths feature adults in abnormal situations where they must confront a challenge that is often impossible or unlikely. For instance, the myth of Perseus and the Medusa features the Greek hero Perseus who was responsible for confronting and defeating the unbeatable Medusa to save Greece.
Fables are designed to be read by and to children, as a means of teaching them basic morality. Fables address simple topics, such as "slow and steady wins the race" or "during times of plenty, prepare for times of necessity." All fables have a short, specific moral point that speaks to the unique needs of children as they grow and mature. Myths can range from stories appropriate for children to stories only appropriate for adults. Myths can be used to explain multiple topics, from sexuality to religious foundations.
Fables can occur in any setting that a reader can understand, often using natural elements such as an ant's mound or a rabbit's home. Fables are not restricted to places that actually exist, as long as the reader is able to imagine that these places exist. Myths are rooted in factual places, or the perception of factual places. The story of Perseus, for instance, begins in Greece a few hundred years before the story was written. Greek readers would have been able to understand and conceptualize the existence of an older Greece. From these beginnings, myths can move into more fanciful settings.