Differences in Naturalism & Realism in Literature
Naturalism and realism in literature are movements and techniques that originated as a reaction against Romanticism where the writers transcended the ordinary to reach the ideal through theme and style. In both realism and Naturalism, writers turned their attention to the depiction of a world that closely resembled the real one, where the characters were not "heroic" but ordinary and recognizable. Although both realism and naturalism have a broad similar goal, they differ in ideology and treatment.
Differences in Character
In naturalism and realism, characters are drawn from the middle class but with a difference. In realism, the character is more important than the plot or setting --- the moral or ethical choices facing the character become the crux of the story. In naturalism, the character is under the will of forces that are more powerful than he is --- hereditary and environmental --- and the frequently unnamed character is given very few choices to make in matters that determine his life and death.
Differences in Plot
The realistic writer will create a plot where events are plausible and can be explained causally, as in the modern detective story. The writer of a realistic novel will avoid dramatic or sensational renditions of events. In a naturalistic novel, the writer will temper the realistic portrayal of events to show the effects and significance of a deterministic universe. Logic and rationality hold very little value in trying to explain events that are dramatized and presented as inevitably leading to despair.
Differences in Themes
The writer of realism chooses themes that closely resemble the themes and ideas of modern, real life. The ordinary struggles of the common man and the hard choices he is faced with form the concerns of a writer of realism. The naturalistic writer chooses to focus on the indifference of the universe as his theme --- the cruelty of the natural world, which does not care about the individual. The action leads to a catastrophe, invariably ending in despair.
Differences in Style
To a writer of realistic stories, describing the character, setting or thing as it exists in reality is a matter of prime importance. There is no exaggeration and no overstatement. To a naturalistic writer, it is important to convey a character, setting or thing so that the mood or atmosphere appears irreversibly doomed. The realistic story will have very little authorial intrusion, and the naturalistic one will have an implicit authorial voice that leads the reader to make assumptions about the presented scene or character.