What makes Chekhov's plays quintessentially modern?
In order to understand what a great leap modernism was on the stage, you must realize that before Ibsen and Chekhov, real life, real people, were not represented on the stage. Instead the stage presentations were exaggerated “romantic” views of social stereotypes, high-blown aristocrats, titled social figures representing the privileges of high society, in unreal, falsely constructed conflicts largely invented from snippets of gossip and hearsay, in witty, unnatural, often highly metaphorical language, taking place in palaces, ballrooms, and chandeliered foyers. The Victorian audiences went to the theatre as a social event, to gossip, to show off their wardrobe, their class, and their wit—orange wenches roamed through the theatre like peanut vendors at a baseball game, entirely oblivious to the play unfolding before them on the stage. Modernism reversed all this “theatricality” and presented real-life environments, psychologically and dramatically accurate characterizations, plot lines emerging logically from internal tensions founded on believable social tensions, moral dilemmas, and personal decision-making.
Chekhov, for example in Three Sisters, put on stage the dilemma of three sisters stranded in a small military outpost village when their military general father dies, unable to flee to their familiar surroundings in the big city--Moscow. The sisters differ in occupation, marital status, and temperament, and their individual conflicts, together with their social dilemma, are expressed and resolved in realistic, non-poetic language. In each play by Chekhov (there are only five), this same attention to realistic presentation is found. When Chekhov does use symbolism (as in The Seagull) it is thoroughly imbedded in the realistic setting. The dialogue itself is all the evidence needed to demonstrate what Realism means--real discussions, real language, a reproduction of the kind of language the members of the audience spoke. In addition, the plays were performed without audience distractions, sometimes in small, intimate spaces, called "chamber theatre", and appealed to all classes.