The main theme of Susan Glaspell’s play is female solidarity. When Trifles begins, Mrs. Hale and Mrs. Peters do not know each other well. They quickly form a team and settle into their task of helping Minnie Wright. As the play progresses, the women not only get along but, through their complementary personalities, uncover numerous clues. Furthermore, their final actions and ultimate inactions demonstrate their empathy for Mrs. Wright, which takes precedence over their possible adherence to the letter of the law.

In the early part of the play, both women—who are both wives—seem comfortable in their supplementary roles in helping the authorities and Minnie. Their conversation and the lines of inquiry they pursue based on the items they find then make them realize that their perspectives may differ from those of the men.

The women’s ability to see beneath the superficial appearance indicates a secondary theme: that women are more perceptive than men. By the play’s end, they realize that their attention to details—especially items that the men might disregard or disparage—has led them to conclusions that would probably prove dangerous, and even fatal, to Minnie. They take her side. The women’s decision to withhold their findings from the men, who embody authority, suggests that men and women have different outlooks on justice.

The theme of Trifles is that men, because they look down on women, make the mistake of not bothering to try to understand them. A more positive way of stating this theme is to say that men would benefit if they took women's experiences more seriously.

The men in this one-act play, first performed in 1916, have a murder case to solve. Mr. Wright was found strangled, and his wife, Minnie, has been arrested as the chief suspect. The sheriff and Mr. Hale, who found the body, bring their wives to the house to pack up some things to take to Minnie in prison. They are all met at the house by the County Attorney.

The men ridicule the way the women, Mrs. Hale and Mrs. Peters, notice small details about the kitchen, calling this a focus on meaningless "trifles." The men ignore the kitchen as a place to search for evidence of a murder motive and tramp up to the bedroom. Left alone and understanding what a farm woman's life is like, Mrs. Hale and Mrs. Peters are able to piece together from the downstairs areas that Mrs. Wright murdered her husband, snapping after he killed her pet canary.

Ironically, the details the men dismiss as unimportant hold the key to solving the crime. However, knowing that the men won't understand that Minnie's was a justifiable homicide, the women decide not to share what they have discovered.

A big theme in "Trifles" is the illustration of traditional gender roles. The men in the play display personalities of purpose and analytical skills in conducting their investigation. The men belittle the women, insisting on man's role as public figure and woman's role in the home. Historically, this public/private dichotomy has been used to instill and sustain the idea that men work in the external world and a woman's place is in the privacy of the home. For example, near the end of the play, Mrs. Peters sarcastically acknowledges that the men would laugh at their evidence and any suggestion that it (evidence) might lead to a conclusion about the crime:

My, it's a good thing the men couldn't hear us. Wouldn't they just laugh! Getting all stirred up over a little thing like a--dead canary. As if that could have anything to do with--with--wouldn't they laugh!

Of course, the dead canary had everything to do with the nature of the Wrights' relationship and a motive for the crime. But since the women knew they would have no voice in the matter, they kept that revelation to themselves. The men continued to look for hard evidence. This is an example of dramatic irony which is when the audience is aware of the fact that the women are finding real clues while the men strut around with undeserved authority, finding essentially nothing significant.

This idea that men should attend to public affairs and women should not is now considered an outdated and misogynistic philosophy, but it was a part of the ideology and culture of male/female relationships in America well into the 20th century. "Trifles" was written in 1916, four years before the 19th amendment was passed which acknowledged women's right to vote.

The women's suffrage movement, the struggle to give women the right to vote, is an important historical anecdote because this play is about the role of a woman's voice. In "Trifles," the women find all the clues that are of any significance. Yet, the men dismiss everything the women say because they (the men) believe that women's opinions should be relegated to knitting, cooking, etc. The men don't see (because of their bias with regard to these traditional gender roles) how a woman can give analytical advice; certainly not any logical observations of something as important as a crime scene. Mrs. Hale and Mrs. Peters do not offer their evidence because they realize it would be laughed at and because they feel sympathy for Mrs. Wright (and are therefore, protecting her).

If women had a voice that men respected, within the context of the play, the crime would have been solved quickly. Going back prior to the crime itself, if women had more opportunity to work in the public world, perhaps Mrs. Wright would have left her husband long before any such crime would have occurred.