In the early ’90s, while he was still in college, Farhadi began writing serialized radio plays for the Islamic Republic of Iran Broadcasting (IRIB), the Iranian BBC. They were so popular that he was soon fielding offers from TV producers. In person, Farhadi is humble, generous and attentive; a number of the actors he has worked with told me of the calm, supportive atmosphere he creates on set. But he also knows how to look after his own interests. After several of his scripts were turned into hit programs, he told his producer at the IRIB that he would continue to provide them with material on one condition: that he do the directing himself. A deal was struck, and at 23 Farhadi was writing, directing and producing his own TV show, “A Tale of a City.” It followed a team of fictional documentarians who, in each episode, made a program about a family or group struggling with a different social issue: poverty, immigration, drug addiction, AIDS. Although scenes were sometimes cut by the censors, the series was widely watched.

In many ways, Farhadi’s first two feature films picked up where “A Tale of a City” left off. Diffuse and episodic, “Dancing in the Dust” (2003) and “The Beautiful City” (2004) are somewhat sentimental portraits of marginalized young people trying to escape their circumstances. His third feature, “Fireworks Wednesday” (2006), is a different matter altogether. Tightly constructed, it observes the classical unities of time, place and action. The movie gives us a day in the life of a troubled middle-class couple as seen through the eyes of a young working-class woman, herself soon to be wed, who is sent by a temp agency to clean their home. It was Farhadi’s first feature film about his own social milieu and the first to draw on his deep theatrical background — qualities that would underwrite the sequence of masterpieces that followed.

Before Farhadi begins shooting, he leads his cast through an intensive rehearsal process, which can last for three or four months. His approach is modeled strongly on that of Konstantin Stanislavsky, the Russian director and theorist, about whom Farhadi wrote his master’s thesis. Instead of practicing the script, the actors improvise moments from earlier in their characters’ lives, producing a back story that will often inform their roles, even if none of it features in the movie itself. The goal is to get the actors to feel as if they had constructed the characters themselves. In “About Elly,” Farhadi’s subsequent film, the title character (Taraneh Alidoosti) is secretly engaged to a man (Saber Abar) who appears only in the final act, after Elly has gone missing. Although they never appear on screen together, Farhadi insisted that Alidoosti and Abar spend a lot of time with each other in rehearsals. It was important, he felt, that each have a strong image of the other in their minds throughout the shoot.

Such a meticulous and — for film, at least — unconventional process has led to performances of astonishing sensitivity. There can be few scenes in 21st-century cinema as moving as the one from “A Separation” in which Nader (Peyman Moaadi), the man speaking to the camera in the opening shot, breaks down in tears while bathing his wheelchair-bound father — tears to which the old man remains oblivious. A moment earlier, we saw Nader, a secular-minded, relatively prosperous individual, behave poorly toward Razieh (Sareh Bayat), the religiously conservative woman he has hired to take care of his father, first accusing her of stealing (wrongly, it turns out) and then roughly pushing her out the door of his apartment. No one deserves to be treated like this, but Razieh has provoked Nader’s anger by tying his father to his bed and locking him in while she runs an errand. This, in turn, may sound almost unforgivable, except that Razieh is pregnant and desperately poor and has been having fainting spells that may be related to her work for Nader — work she has had to keep secret from her equally religious husband, who would be scandalized to know she was taking care of an old man. And Nader himself, we realize as the slightly shaky camera lingers over his heaving body in the bathroom, already seems to feel remorse for his actions. Almost every moment in the film invites, and rewards, this kind of in-the-round moral scrutiny. The power of the bathing scene arises not simply from the poignancy of the action it depicts (the son now caring for the father who once cared for him) but also from the way in which, after a relentless sequence of increasingly hostile exchanges, it provides a kind of release valve for an accumulation of complicated, contradictory emotions — Nader’s and our own.