Rooney leaves you with a lot to think about. Your esprit de l’escalier doesn’t kick in until you’re well out the door. When she was a teen-ager, she joined a writing group at a local arts center. One of its organizers, Ken Armstrong, said that, even then, there was “a thread of steel running through her.” I wanted to know where Rooney got her mettle, how a Marxist ended up writing a book that sits alongside body lotion and silk pajamas in GQ’s “30 Fail-Safe Gifts for Her” guide; how she upended the conventional wisdom that a writer should show and not tell, that characters shouldn’t say what they think, in the process creating some of the best dialogue I’ve read. There is a quiet but insistent sense of challenge in her writing. It makes you wonder whether you’re wearing the moral equivalent of a long necklace.

We are living in a great epistolary age, even if no one much acknowledges it. Our phones, by obviating phoning, have reëstablished the omnipresence of text. Think of the sheer profusion of messages, of all the things we once said—or didn’t say—that we now send. “You don’t have any news you’ve been waiting to tell me in person, do you?” Nathan, a software developer, asks Sukie, his much younger roommate, upon picking her up at the airport, in “Mr Salary,” a short story that Rooney published, in 2016, in Granta. “Do people do that?” she says. “You don’t have like a secret tattoo or anything?” he continues. “I would have attached it as a JPEG,” she replies. “Believe me.” Rooney told me, “A lot of critics have noticed that my books are basically nineteenth-century novels dressed up in contemporary clothing.”

The Internet isn’t Rooney’s subject, any more than the letter was Austen’s, but she has assimilated online communication into a new kind of prose. “She does it in a way that’s totally natural,” Bohan, her agent, told me. “Whereas, if it were someone in his or her forties or fifties, it’d sort of be, like, ‘I Am Writing a Novel About the Internet.’ ” Rooney told me that in “Conversations with Friends” she was interested in exploring “e-mail voice,” the way that Frances and her friends “curate their styles of communication online.” This isn’t a flashy conceptual move; it’s just that e-mails, texts, instant messages, and Facebook posts are an unquestioned part of her characters’ everyday routines. A novel without them would be like a novel without chairs. After an illicit kiss, Frances receives an e-mail from Nick, and forces herself to wait an hour before responding. “I watched some cartoons on the Internet and made a cup of coffee,” she recalls. “Then I read his e-mail again several times. I was relieved he had put the whole thing in lower case like he always did. It would have been dramatic to introduce capitalization at such a moment of tension.” Reading our lives, we are all New Critics.

Later, Frances and Bobbi try to watch the movie “Brazil,” but Bobbi falls asleep. “I didn’t feel like watching the film on my own,” Frances says, “so I switched it off and just read the Internet instead.” An older novelist might have written “surfed the Internet” or “looked at the Internet,” but “read the Internet” has the ring of native digital literacy. There’s also something current about the flatness of Rooney’s tone; like “breaking the Internet,” “reading the Internet” makes a little joke of the juxtaposition of a puny active verb and the vastness of the thing upon which it is acting. Rooney’s transposition of Internet voice to the page brings a certain tension to her narration. When Frances observes that “Melissa used a big professional camera and kept lots of different lenses in a special camera pouch,” it’s impossible to tell whether she’s impressed by Melissa or mocking her. As with a tweet, you might interpret the sentence either way.

Perhaps refreshingly, for an Irish writer, Rooney has been received as a voice more of her time than of her place. The Times called her “the first great millennial author.” She was born in Castlebar in 1991. Marie Farrell, her mother, taught math and science and spent two years volunteering in Lesotho in the eighties. Eventually, she became the director of the Linenhall, a community arts center in Castlebar. (“A lady with no airs but an abundance of graces Marie Farrell eschews the stereotype arty image betimes associated with the discipline,” a tribute in the local newspaper read.) Kieran Rooney, Sally’s father, worked as a technician for Ireland’s state-owned telecom company. (It was privatized in 1999.) He and Farrell took Sally and her two siblings to church, but they were more passionate about passing on socialist values. Marx’s dictum “From each according to his ability, to each according to his needs” was the household catechism. During the financial crisis, which ravaged Ireland’s economy, Kieran took an early-retirement package.

Farrell recalls Rooney as a quickly frustrated child who wouldn’t countenance anything that didn’t interest her. (Rooney says that the trait endures, and claims “excessive laziness at anything I’m not good at.”) High school, at St. Joseph’s Secondary School, an all-girls institution where Rooney had to wear a “blue sweater, gingham shirt, and lumpy gray pinafore, which I loathed,” was a particular trial. “I just found it kind of baffling, the whole institution of school,” Rooney said. “I was, like, Does no one see that this is repressive, and that there are more of us than there are of them?” She boycotted homework. “My parents were very much, like, Fight your own battles,” she recalled. She spent hours online, “more comfortable with text than with actual personal interactions.” She said, “I was someone who, in a very disorganized way, was thirsty for knowledge. I liked having access to anything I wanted to know. I still find myself using that aspect of the Internet a lot. I usually have ten open tabs on my phone browser, and they’ll all be, like, ‘What is the boiling point of gold?’ Or ‘frogfish chameleons.’ I saw a frogfish on a nature documentary, and I wanted to know if they are genetically related to chameleons, because they have similar facial characteristics. I don’t think I found anything conclusive.”

Rooney began writing stories as a teen-ager. She says that they were terrible (“possibly my understanding of human beings was just not that sophisticated”), but she was already drawn to certain scenarios. “Couples, triads,” she said. “If you took something I wrote when I was fifteen, it would be the same, plot-wise, as now.” At eighteen, she published two poems in The Stinging Fly, a Dublin literary journal, which she now edits. One of them, “Tírghrá,” began:

I sit in my grandmother’s living room— the patterned carpet, spools of thread the 1994 hunting trophy, dried flowers china ornaments, a chipped ashtray— and she talks about her childhood.

I am dreaming of industry, art galleries of fashion, sex and cocaine and the distance between you and I east across the colourless Irish Sea.

In 2009, Rooney moved to Dublin to attend Trinity College. She hoped to do a double major in sociology and English, but was accepted only into the latter program. She found herself in proximity to a social milieu that she hadn’t known existed: the classmates in “waxed hunting jackets and plum-coloured chinos,” as she writes in “Normal People,” whose parents had “not figuratively” caused the financial crisis that claimed her father’s job. “What I wasn’t prepared for was encountering the class of people who run the country,” she told me. “I had a feeling, on one hand, of being appalled, but on the other hand a real sense of wanting to prove myself to people, to prove I’m just as good as they are. I don’t know why—it would have made a lot more sense to just let them be—but it’s a fascination that’s not purely revulsion.”