The play is realistic in that it is based on the Hossack’s case, a real murder incident in Iowa on December 2, 1900, when Susan Glaspell was a news reporter. The language used in the play is plain and simple, the way real people in a small town would speak. There are no dramatic monologues or soliloquies to draw attention to explicit themes. There are no dramatic climaxes for effect, no smoking gun, no confession. All these would be found in a Romantic novel, not a realistic play. No, Trifles never draws attention to itself: it wants to be overheard instead of heard. Glaspell is very subtle as to the differences between the genders. Her play is psychological drama: what is not said is as important as what is said. Who doesn't appear is as important as who does appear.
The two main characters are realistic, a seemingly normal husband and wife. Glaspell deals with them realistically: they never appear in the play at all. They must be reconstructed by others on stage and us, the audience. This, by definition, is realism: the representation in art or literature of objects, actions, or social conditions as they actually are, without idealization or presentation in abstract form.
Where Glaspell blurs the line is in the last part, "in abstract form." Because we never meet or see Minnie, she is nothing but an abstract form. It should be easy to romanticize her. And the men do this. Her husband reified her, turned her into an object. The men on stage likewise describe her abstractly as a "wife" or a "murderer." But, Glaspell's depiction of Minnie by the women is realistic. The women know--even by the way she stitches the quilt--that she is a real person.
The play, as a whole, is an example of symbolic realism. Below is the table of contents from a book which deals thusly:
Symbolic Realism in Susan Glaspell’s Trifles
Table of Contents
II. Minnie’s Misery and Her Brutal Way out 4
A. The Signs of Isolation and Silence 4
B. A Marriage without Love 7
C. Minnie’s Suppressed Creativity 8
D. John’s Strangling as the Symbolic Revenge 10
III. Glaspell’s Critique on Gender Roles 11
A. Symbolic Characters’ Names 11
B. Women’s Superiority in the Investigation Process 13
C. The Quilt as a Text to Be Read 15
So, the characters are realistic and representational. The characters stand for real people in a real small town. And the characters stand for people like these people: abusive husbands, abused wives, members of a male-dominated justice system, wives as domestic servants. Glaspell blends realism and symbolism and psychology to achieve a one-act tour de force that is no trifling matter.