Fantasies are capable of revealing new insights about reality and satisfying the modern-day hunger for myth. They raise questions about the struggle of good versus evil and the meaning of life. Many of the themes of fantasy are rooted in traditional folklore and in the human psyche. The modern literary fairy tale is told in the form of the traditional folktale but has an identifiable author. Hans Christian Andersen is considered to be the first author of modern fairy tales. Specific criteria for the evaluation of fantasy include noting the believability of the fantastic elements, a logical internal consistency, an original and ingenious plot, and a universal truth. Fantasies are written at several levels and include many elements. Some elements are animals, toys and dolls, small worlds, strange characters and events, unusual worlds, magical powers, the supernatural, time shifts, and kingdoms. The most complex stories are called high fantasy. They have recurring themes and motifs, especially conflicts between the forces of good and evil, and usually feature heroes with a quest. Many high fantasies are told in a series of books and touch on themes at the core of life. Science fiction differs from fantasy in that it speculates about what might happen if the knowledge of science today was used in certain ways. Certain conventions apply to the writing of science fiction to make it believable. Science fiction is valued for its ability to stimulate the imaginations of children and to consider ethical and social implications of scientific issues.