Naturalism is a literary movement which focuses on very specific aspects of life. The characteristics of Naturalistic texts contain the following ideals:
1. The text is written from an objective point-of-view. This means that the author writes from a scientific perspective similar to that of an experiment. The author states that they are simply describing the action of what is happening- they do not attempt to change or influence the character or the action of the text in any way.
2. The characters described are typically deterministic. The protagonist simply sees a problem with the circumstances that they have found theme selves in, or other characters in, and wishes to change them.
3. Given the text is written from an objective point-of-view, the text is also pessimistic and emotionally cold. The author is, again, only describing what they are "seeing" from a observers point-of-view. They wish to have no compassion for the characters because it would force them to interfere with the action of the story.
4. The setting is one you would find in everyday life. There are no spectacular scenes in regards to elaborate castles or upper-class niceties. The settings are typically set in lower-class homes and workplaces.
As for the play "A Streetcar Named Desire", there are many different aspects of Naturalism depicted in the play.
Scene One: First and foremost, the scenery of the play depicts the ordinary. Elysian Fields is described as ordinary and poor. The buildings are described as "raffish". The characters of the play also support typical Naturalistic characterizations. The men are blue collar workers and the women deal with abuse. Three times throughout the play domestic violence and rape is depicted. (These show the assumed lower class actions of the people who live here.) The setting is also set by the music of the lone blue piano. The piano sets the mod for the entire play- one of solitude and depression.
Scene Two: This scene offers another aspect typical of Naturalistic literature. Stanley comes to find himself in circumstances beyond his control- Stella has invited her sister to stay with them. Given that Stanley is not happy about this, he does come to find out that Belle Reve has been sold- he, wanting to find a way to make this situation better, believes that getting money from the sale would make his life more bearable. Unfortunately, like all Naturalistic literature, this is not the outcome of the piece. Instead, there is no money and Stanley decides to take something else from Blanche by raping her- what is left of her sanity.
This being said, Williams is not typically depicted as a Naturalistic writer. He is normally placed in either the Modern or Post-Modern periods. Regardless, "A Streetcar Named Desire" does hold typical Naturalistic characteristics throughout the play.
See Historical Context link for importance of scenery.
See Style link for importance of motifs.