Greta Gerwig not only stars in Noah Baumbach’s new comedy “Mistress America,” a modern screwball farce in which she plays Brooke, a flighty New Yorker who befriends the Barnard College freshmen whose mother is going to marry Brooke’s father, only to become the subject of a story the girl composes for a class. As was the case with his much-praised “Frances Ha,” she co-wrote the script with him, and discussed their collaboration in a recent Dallas interview.

“It’s the second time we’ve written together,” Gerwig explained, “and the third I’ve acted in. The first one I didn’t write at all. I was just an actor.” She quickly added that her comment wasn’t intended to denigrate acting: “Somebody described the difference between making a film—producing it, writing it—as being a parent. You’re there all the time for the highs and lows and everything in between—you’re intimately involved in it. And being an actor is like being a grandparent—you can come and play and then go home. I’ve always thought that’s true.”

Gerwig continued, “Writing together [with Baumbach] is always really, really fun and effortless. We got a sense that we would work well together when I was acting in ‘Greenberg,’ and then when we started writing ‘Frances Ha,’ it was the same kind of experience as it is writing now. We talk a lot, we talk about stories and movies and characters, and then we go away and we write separately to generate content, and then we trade pages and edit each other. And then we do it again. And we build this thing, and start pounding it into the shape of a movie. We’re both really serious about the words, saying the words exactly as we’ve written them. There’s no improvisation.”

When asked whether she shares a view of life with Baumbach—with whom she also lives—Gerwig observed, “I think we’re actually kind of opposites as people and have kind of different life views in a way. But I think that’s what makes the collaboration really sparkle. Our opposites make it richer, if that makes sense. I’m more gushy—I’m a softie. And he’s like a laser beam, super-sharp. He has a more critical eye, in a good way, and I’m more like, ‘I love everybody!’ I think between the two of us, we work really well together—I like waking up and just instantly start talking about what we’re writing, even before coffee. I like being completely absorbed by something.

“On set it’s the same way. He’s an amazing director, and I trust him and know he’ll get the best performances out of everyone. In post-production I’m very involved with the music and the editing. But on set I’m no different from any of the other actors, and I don’t feel like writing it necessarily gives me a secret guide to how to do it. Even though I wrote it, I struggle the same way as if I hadn’t. The only time it’s hard is when we’re working on different projects, because then we both only want to talk about our own project. That’s when we get mad at each other,” she added with a laugh.

“When we wrote Brooke,” Gerwig continued, “her nature as a small-time hustler who’s got a lot of irons in the fire, it just felt very New York to us, like a certain type of woman that we both know. We wanted to create all those little pinpricks of where she was in the world…so that you realize her life is complicated and confusing. She’s got all this confidence and is so enthusiastic. She’s really performative, always putting on a show for whoever is in front of her, and in a way that hides a lot of her insecurities and loneliness. She has a sadness and loneliness in her, and I think that’s what Tracy [the student played by Lola Kirke] sees in her, and that’s what she writes about in her story. She’s a really fascinating character, and I love Brooke. But I love all the characters in the movie. If I didn’t, I couldn’t write them.”

But Gerwig noted that Brooke isn’t her. “If anything, the character I’m most like is Tracy,” she said. “I went to Barnard College. We shot on the floor where I lived freshman year, when I was eighteen. Her ambition to be a writer, her quietness, her awkwardness and then coming into her own—that was all more what I was like. I think that movies don’t necessarily portray the loneliness in college that’s so pressing for the first few months. Brooke was the kind of person I admired, but who also scared the crap out of me.

“I like [‘Mistress America’] being called a screwball comedy,” she emphasized. “For me, because my first love was theatre, the screwball comedies—of Howard Hawks, Preston Sturges, Ernst Lubitsch, George Cukor—even if they weren’t literally filmed plays (though some of them were, like ‘Holiday’), they had a feeling of being almost like a play, with a bunch of people talking in a room. And they shot them from far away, so you could see the actors’ full bodies. Even when I was young, these were the movies I responded to, with fast-talking, walking actors. I like that kind of stuff.”

As to her own future plans, Gerwig said, “For me, writing and creating and directing—hopefully more directing my own work—is the most fulfilling to me. I love acting, and will always keep acting. But I think it’s always helpful to know what your true north is, and what you’d drop everything for. If you don’t know that, you feel at the whim of the world. It’s not that I wouldn’t act in very different kinds of movies; it’s more that if I have a movie I’ve written that I was going to produce and direct, that would be first in line, and everything else comes after that.

“I love all different types of movies, and I’d like to try a lot of different genres. But I don’t love car chases. I think they’re boring. I always kind of zone out during a car chase. So I probably wouldn’t make a movie with a car chase. I think the kind of movies I make will generally fall into the category of ‘talkies.’

“That’s what I make. I make ‘talkies.’”