Spike Jonze, writer/director of “Her.” (KEVORK DJANSEZIAN/REUTERS)

“Her” sounds like a gimmick.

In not-too-distant-future Los Angeles, Joaquin Phoenix falls in love with an operating system, voiced by a never-seen-on-screen Scarlett Johansson.

As an elevator pitch, it gets a grin. But as a film, it transcends quirk and mere novelty. “A Spike Jonze love story,” read the promotional posters that feature the director’s name next to Phoenix’s face and penetrating blue eyes. That simple, classic description — “love story” — is the most accurate way to describe the best film yet from one of the era’s most playful and ambitious directors.

After all, the movie is not called “It” or “OS” or “Virtual Love.” It’s called “Her.” By the end of the movie, viewers won’t ask, how could he fall in love with a machine? They’ll ask, how could he not fall in love with her? The relationship that unfolds between Phoenix’s Theodore and Johansson’s Samantha — the discovery, vulnerability, heartache — is real.

Of course, the notion of reality is one that Jonze has toyed with and gleefully distorted over the course of his career, from the portal into the body of the titular actor in “Being John Malkovich” to the extrasensory fantasy world of “Where the Wild Things Are” to whatever it was that happened in the final third of “Adaptation.” (This theme even extends to the prank-centric world of MTV’s “Jackass,” a show that Jonze co-created.)

Ask Jonze to explain his version of reality and the answer you get is honest, tangled and just out of reach. Pretty much how you’d expect it to be.

“I feel like every movie, I’ve learned more and more about what I think of the world and what I’m trying to figure out. But in terms of what’s real to me . . . I think if something’s emotionally real — and I’m not even talking about in movies or in art, but in life — you can’t really argue with that even if your intellectual mind might know differently. Your emotional mind [doesn’t]. It doesn’t matter how smart you are.”

In early December, Jonze is in D.C. to promote “Her.” It’s his first film since 2009’s “Where the Wild Things Are” and his first solo writing venture. The visit is something of a homecoming for Jonze — born Adam Spiegel — who spent most of his teenage years in the area and attended high school at the Field School and Walt Whitman High School. He liked skateboarding and going to punk rock shows, and those two activities would help form the foundation of his early career. After a post-high school move to California, he first made a name for himself making stylized videos of skateboarders and then became the definitive (and a quite prolific) music video director of the 1990s alt-rock boom. “Sabotage” by the Beastie Boys, “Buddy Holly” by Weezer, “Praise You” by Fatboy Slim — these are just three of his videos that were in the heaviest of heavy rotation on MTV in the Lollapalooza Era.

Jonze is only vaguely interested in speaking about his personal past, and even when he does, he relates it to his current creative process. He talks about ’80s punk concerts he saw at the Wilson Center in D.C. and how listening to hard-core icon Minor Threat 30 years later isn’t simply an exercise in revisiting the past.

“It’s not pure nostalgia, because it means something to me right now, and not just because it meant something. It’s talking to me right now, at 44 years old, and it’s making me think about who I am and what I believe and what I stand for.”

He compares the sensation to flashbacks that Theodore experiences in the movie, when thinking about his ex-wife (played by Rooney Mara).

“They’re not past tense,” Jonze says of his character’s flashbacks. “They’re not, ‘Here’s what happened in the past.’ They’re present tense because they’re happening to him. It’s what he’s thinking about presently — what’s happening, what he’s obsessing on, where’s he’s stuck in the present moment.”

It’s an explanation with just the right amount of clarity, which is Jonze’s speciality.

“He creates this sense of an alternate reality that still feels very grounded and real,” says actor Chris Pratt (“Parks and Recreation”), who plays Theodore’s gregarious co-worker, Paul, in the film. “He touches on these themes that are very practical, but in a world that is a small slice of a different world.”

It’s an approach that has served him well over the years, says friend and frequent collaborator Lance Bangs.

“He does set up a lot of situations where . . . it’s not ‘Star Wars’ with aliens and makeup and pure fantasy stuff,” says Bangs, whose job as documentarian of each movie Jonze directs give him a unique vantage point. “It’s stuff that looks like the real world or has a verisimilitude, that kind of take on magical-realist.”

The world Jonze creates in “Her” is an L.A. that is far from the dystopian nightmare seen in many future-set movies. The Los Angeles of . . . is it 2040? Something like that? Seems like a pretty nice place. There’s high-speed rail, minimal traffic, men wear goofy/charming high-waisted pants, people still go to the beach.

“Everything is nice and comfortable and yet he’s still lonely and longing for connection,” Jonze says of Theodore. “It seemed like it would hurt more, in this beautiful pop world, to have that deep melancholy.”

As the forlorn Theodore, Phoenix reaches yet another career height in “Her.” He spends much of the film on screen by himself, showing both sides of an intensely blossoming relationship.

Jonze, who is always soft-spoken and careful with his words, becomes even more selective when describing working with Phoenix.

“Without sounding dramatic, it was a real” — he pauses, not for effect, but searching for the right phrase — “really important life experience that I got to have with him, making this.” Jonze compares working with Phoenix on a computer love story to working with the child actor Max Records on “Where the Wild Things Are.” Both versions of a fantasy were an “adventure” for Jonze and his actors. With Phoenix especially, though, he calls it “hard to talk about too much,” it was an “intimate ad­ven­ture.”

“He’s challenging in the best way,” Jonze continues about Phoenix. “None of his challenges are coming from a place of ego, a place of pride. They’re coming from: ‘This doesn’t feel right! I don’t know! It’s me, I know I’m being stupid, I’m sorry!’ And often times, when he challenges is when I’m forced to raise my game. To dig deeper. . . . And that’s what made it such a great experience, the way we pushed each other.”

For his part, Pratt felt a considerable push from Jonze.

“He wore me down, I think. That’s probably the best way to put it,” he says. “It was tweaking and retweaking and throwing out and re-creating, over and over again. Even with just my character, and I’m in five scenes in the movie. So he’s very much into the details, and he wore me down. He’s not one of those directors who yells at you through a megaphone. He’s really gentle and thoughtful. He was helping me find it in the moment and it might have been that I just didn’t give him exactly what he wanted or maybe he didn’t know what he wanted. But we were finding it.”

It took Jonze a while to find exactly what he wanted with “Her.” Specifically with Her. After wrapping shooting with British actress Samantha Morton in the starring role, Jonze decided she just wasn’t the right fit and Johansson was brought on to provide the voice of Samantha.

“I think in the ideal world, I would have had somebody unknown,” Jonze says. “But it needed somebody with a presence. It needed somebody who was a great actress, that has confidence, that is attractive and has charisma. All of that comes through in her voice.”

The role isn’t your typical voice-over role like in an animated movie. Johansson has to play Samantha as an entity that literally comes into existence at the click of a button and quickly proceeds to become “a fully formed being trying to figure out who she is and having these sort of existential questions the same way we have existential questions,” Jonze says.

The film is garnering near-universal praise from critics, including earning top honors from the National Board of Review and a Golden Globe best picture nomination in the comedy category. (It’s not exactly a riot but has plenty of laughs, some of them provided by Jonze himself, who supplies the voice of a particularly vulgar videogame character.) Whether general audiences will be as receptive to the themes and ideas is less certain.

After a packed Georgetown screening that was followed by a Q&A session with Jonze, one viewer asked if he found it unsettling that the only sex scene in the movie featured a person by himself. Jonze listened politely to the question — which seemed to completely miss the point of the entire world he’d created, where a man and a disembodied voice fall deeply in love. He had a thoughtful answer ready: Some people may find the central conceit creepy, while some may find it sweet.

In conversation the next day, he crystallizes what makes Theodore and Samantha work. “When he accepts her for what she is. When she’s not pretending to be something she’s not and when he’s not wanting her to be something she’s not. Which is any age-old relationship,” he says. “When you stop projecting on the other person, when you stop pretending you’re someone else, when you actually get to know each other.”

And that makes perfect sense, the recipe for love between any man and the computer that he purchases that devours millions of pieces of information per second on a quest to better understand humanity.

“There’s a bit of fantasy to his work,” Pratt says. “It’s kind of like how he is. He seems a litttttle bit like he’s from a planet that’s very similar to Earth but is not quite Earth. You know? And it’s a kind of planet you hope Earth will turn into. He’s very evolved.”