Research the story if you are unsure whether it is realistic fiction or nonfiction. If the story is nonfiction, every character and event will really exist or have happened. If a single character or even a single conversation was invented, the story is realistic fiction. "The Killer Angels" by Jeff Shaara, for instance, is a type of realistic fiction called "historical fiction" because, while it involves real historical figures fighting the Battle of Gettysburg, Shaara invented the characters' dialogue and thoughts. However, "The Six Wives of Henry VIII" by Alison Weir is nonfiction because Weir did not invent any of the details.
Determine whether the events in the story could possibly happen — not whether they are likely, but whether they are possible. If the story includes unreal elements such as magical beasts or supernatural powers, or if it includes scientific advances that do not exist yet such as faster-than-light travel or colonies on other worlds, it isn't realistic fiction no matter how believable the characters might be. Conversely, if there are no completely impossible elements, the story is realistic fiction even if it includes extremely unlikely events such as international conspiracies or child spies.
Examine the way the story treats any animal characters. Strongly realized animal characters do not necessarily make a story unrealistic as long as the animals do not talk or perform other unrealistic actions. For instance, "The Call of the Wild" is realistic fiction even though its viewpoint character is a dog because the dog acts the way a normal dog would; he does not talk or understand human speech beyond basic commands, and human motivations are beyond his comprehension. However, "Animal Farm" is not realistic because the animals talk, write, stand upright and wear clothing.
Determine whether the narrator is reliable and if the way he sees the world affects the realism of the story. Some realistic fiction stories appear to have impossible elements because their narrators are insane and see bizarre things happening around them. For instance, in Edgar Allan Poe's "The Tell-Tale Heart," the narrator hears a dead man's heart beating, and in "One Flew Over the Cuckoo's Nest" by Ken Kesey, Chief Broom sees people turning into rabbits. However, because the narrators are insane and could have these hallucinations in real life, the stories are considered realistic fiction. If the dead man in "The Tell-Tale Heart" really were some kind of zombie and the people in "One Flew Over the Cuckoo's Nest" really could change shape, the stories would not be realistic fiction.