One theme of realist literature is a commitment to describing the physical environment exactly as it is perceived. It uses language that relates to your senses. Characteristics that cannot be sensed are not within the means of realist writing, although that did not preclude realist writers from writing about intangible characteristics and emotions in their descriptive writing.
Realists, in their efforts to represent and express the physical world, took an interest in the society around them. They sought to apply the same kind of realist descriptive approach to society as they did to nature or to people. This is part of the reason why realist writers such as Upton Sinclair wrote work that at times appears like contemporary investigative journalism.
Another theme of realist literature, especially American realist literature, was its rejection of romanticism. Realists were not prepared to accept a romantic, or as they saw it, naive understanding of life. They saw society and relationships not necessarily cynically or pessimistically, but with an onus on representing whatever it is that is real. Whether it was sex, women's plight or racism, they wanted to express the truth of the American experience.
Realist literature, in its concentration on truth, was interested in the scientific method and the best routes towards discovering reality. One result of that focus, as well as the rejection of romanticism, is the use of common or ordinary figures as central subjects. Unlike many romantic texts, realism was less interested in the great or famous. Realist literature often focuses on an average citizen chosen because he represented a particular societal trend.