“Inherent Vice” is an unconventional detective comedy-drama set in trippy 1970 Los Angeles. The first film adaptation of a Thomas Pynchon novel, it shows U.S. society as psychedelic disarray, everyone struggling to get, and keep, their unstable feet on the ground. The populace jumps from outlaws to nice dudes, antisocial creeps to lovable guys.

In other words, it’s a perfect zone for Joaquin Phoenix.

Phoenix stars as “Vice’s” lovable sleuth, a doper who gets tangled with the police after waking up in a massage parlor beside a corpse. It’s the latest twist in an A-list acting career built by choosing the unpredictable and audacious.

There has been a misstep here and there — such as his weird-beard phase during 2010’s “I’m Still Here,” a perplexing mockumentary in which he pretended to quit acting and try rapping. His successes are much more common.

In Ridley Scott’s “Gladiator” (2000), he was villainous emperor Commodus. He converted into honky-tonk hero Johnny Cash in James Mangold’s “Walk the Line” (2005). In Paul Thomas Anderson’s “The Master” (2012) he played World War II veteran Freddie Quell, a reckless alcoholic sex fiend, gaining him his third Oscar nomination. Moving into the near future he became geeky greeting card writer Theodore Twombley in Spike Jonze’s sensitive computer romance “Her” (2013).

Now 40, and 30-plus years into performing, Phoenix deems some actors more artistic than he is.

“I never went to acting school. I never learned, like, the fundamentals of what you’re probably supposed to do,” he said in a recent phone conversation. “I talk to other actors and they talk about how they cover things and I’m like, ‘Wow, that sounds amazing!’

“There are some actors I know that talk about the characters and the research material, and they sound like scholars. They’re just geniuses, and man, they remember everything.”

Bringing Pynchon’s oddball central character and his rich, rhythmic writing to the screen was an uphill climb, he said. “This book that it was based on, it’s so rich and [has] so many details, but I’m kind of like a kid that crams for a test, that never remembers anything, like, once the test is over.

“It was really tough. Early on I was really stuck on the dialogue. I wanted this dialogue that was straight from the book, ’cause I just loved it so much, he’s such a great wordsmith. I kept trying to make it, and it just wasn’t working. It didn’t seem believable. Ultimately I had to do a kind of condensed version of it. And I felt so disappointed in myself. I felt like I’m doing something wrong.”

Anderson, directing Phoenix for the second time, told him not to sweat it, just focus on “stuff that’s a great joy to say. This is the great part of adapting the things you just love in a book.”

Making another film together was a pleasure, Phoenix said. While they were filming “The Master,” Anderson fondly called Phoenix “Bubbles,” his pet monkey. He was that playful in “Inherent Vice” as well, teasing him to keep his spirits up.

“This was really a playful set, really a joyous set, a lot of fun to work on it. It’s part of Paul. He can manage to have so many disparate tones in one film because he’s like that. There’s a part of him that’s very deep and emotional and part of him that’s just like a ridiculous 8-year-old, that’s just like me. That likes fart jokes and stuff, you know?

“Man, I don’t think I’ve ever laughed as hard as I have when I worked with Martin Short,” he said, whom he had idolized since “Three Amigos,” one of his favorite movies. “We worked very late and did so many takes because I couldn’t stop laughing. Every time there was a take he’d say something new or make a gesture that just was hilarious.”

He had a similar experience in his upcoming Woody Allen film with Emma Stone, which he can’t discuss in detail, subject as it is to the usual Allen secrecy. Working with actors and filmmakers of real talent is one of the best experiences in his career, he said.

“When they talk to you, you like the way that they describe the world and what they’re after emotionally. You know, it’s just like you fall in love with somebody. You go, ‘Oh, I want to work with them. I want to hear what they have to say.’ The big thing is that they work with people that are better than you and smarter than you, and that’s what I try to do.”