Shining through the dialogue, the play's tone is both dark and light. The overall dejected feelings of the characters makes the tone dark. However, this factor provides a simultaneous lightness, because the characters feel too bad for themselves to be taken seriously.
This simultaneous darkness and lightness arises as a result of the pathetic qualities of the characters and action. For example, the play reaches its climax when Voynitsky attempts to shoot Serebryakov towards the end of the third act. However, Voynitsky misses, "[hurling] the revolver on the floor and [sitting] down on a chair exhausted." His inability to shoot Serebryakov fits well with Voynitsky's words and actions overall. He talks a lot about his capacities and regrets, but never does anything of substance. Throughout the play, the two men's mutual lack of follow-through and talent makes it hard to take their squabble seriously. The characters are a group of mostly helpless, out-of-touch people, who never do anything to change their lives. It's difficult to decide whether their pathetic nature is more sad or funny.
However, the play ends with a surprisingly earnest, hopeful tone. At the end of the fourth act, Sonya delivers a gripping speech that sounds like a prayer. After Astrov has rejected her, she has witnessed her uncle and father get into a violent yet pathetic fight, and her father has once again left her behind for the city, she accepts her seemingly fated loneliness with courage and strength. Sonya is the play's youngest character—Marina calls her a "motherless child"—yet in her grief, she takes it upon herself to care for and encourage her cynical uncle. She tells him and herself that they "shall live," acknowledging that it won't be easy but that after they die they will "see a life that is bright and beautiful and full of grace." As the play ends, Sonya's repeated statements shift from "We shall live" to "We shall rest." These are the final words the audience hears before the curtain "slowly falls." This shift in tone leaves the audience moved yet ambivalent about how to feel about the play overall, as its tone has constantly vacillated between dark and light.