We are meeting in Cannes to discuss Woody Allen's Irrational Man, in which the 26-year-old has a crush on her unhinged philosophy professor played by Joaquin Phoenix, 40. Does she mind such an age difference in real life?
"It probably depends on the person and what their individual feelings are on the subject," she says.
Stone wanted to work with Phoenix and the pair share a sparky chemistry on screen.
"He's one of my favourite actors," she admits. "I've never worked with anyone who's so incredibly alive and wild, so raw. I've never felt so intimidated by another actor."
Stone needed her defences to be on alert as her Jill character enters murky waters as Phoenix's Abe commits a murder to elevate himself out of his existential funk - and to get his libido back.
"If somebody tells you they are crazy," Stone asserts, "you should believe them. Instead of being this woman who swoops in to save Abe from feeling sad and depressed.
"Jill wants that energy in her own life because she feels too pure. She doesn't want to be this sensible middle-class girl who's well-adjusted and clean cut. She knowingly pulls this toxic energy into her life and I found that very interesting."
Given that Diane Keaton, one of her idols, was a former Allen squeeze and onscreen muse, did she want to step into her shoes, now she has worked with the director for a second time after Magic in the Moonlight?
"Well, not necessarily," Stone responds, lowering her raspy deep voice. "Diane can step into her own shoes."
I cite Interview magazine, in which the kooky Keaton interviewed Stone, calling her "unconventionally beautiful". Keaton says Stone considers "things like complexity and a certain kind of off-kilter aspect to a person as important components of beauty".
"Oh Diane, God I love her!" Stone chortles.
So is she complex and intellectual?
"Yes, I'm severely complex and very intellectual. My lack of university experience will tell you that."
Does she feel bad about that? "I did for a while. The year all my friends graduated from college was a very strange year.
"Until age 22 I felt like I'd escaped the system. I was working pretty steadily at that point but, still, for that whole year I was like, 'Does this mean I'm not intelligent if I didn't go to university?'
"Now I realise that learning and education are completely different things and you can still be an intelligent person who loves to learn without having gone to college. Working on these films, everything is like a master class. So I know I made the right decision."
Born Emily Stone, the fledgling performer reverted to Emma as there was another actor with the same name.
Young Emily, raised by Krista, a homemaker, and Jeff, a contractor, in Arizona, was determined to pursue a career in acting and comedy. Already feisty at age 12, she convinced her parents to homeschool her so she could attend auditions.
"My dad was a big fan of 70s comedy and my mum loves Saturday Night Live, so that's what I saw growing up."
Stone has now appeared twice on SNL and counts Steve Martin as one of her all-time favourites.
Her mum has been her guiding light. Krista battled to overcome breast cancer, the disease that also took the life of Spider-Man and Pretty Woman producer Laura Ziskin, with whom Stone was very close.
The actress has put considerable effort into breast cancer awareness via her work with Revlon and Stand Up To Cancer, an organisation Ziskin helped establish.
To celebrate her mother being five years cancer-free in 2013, she convinced Sir Paul McCartney to sketch two birds' feet for tattoos for her and her mum since Krista's favourite song is The Beatles' Blackbird. "Cancer is a complete epidemic," Stone says emotionally.
"Everyone has either experienced it themselves or has known or been related to someone who's experienced it."
She commends Angelina Jolie for revealing her own struggle, her 2013 double mastectomy and the removal of her ovaries and fallopian tubes last March.
"When she spoke about the BRCA gene she has, the number of people getting tested for the gene skyrocketed. She's an incredible woman."
Stone is currently trying to be adventurous in her movie choices.
Opting to make the disastrous Aloha with bigtime Hollywood director Cameron Crowe was hardly a surefire bet.
Now she is set to work with relative newcomer, Whiplash director Damien Chazelle in the movie musical La La Land. In this she co-stars for the third time with Ryan Gosling (after Crazy, Stupid, Love and Gangster Squad) as well as Oscar winner JK Simmons.
In the story, Gosling's jazz pianist and Stone's aspiring actress fall in love but face difficulties as they become more successful. Oh no, more singing!
"I don't think I could ever do a stage musical again," Stone concedes. "But this is a movie and you can record it and you're only singing for a day. I'm very excited. Ryan is great to work with and Damien is fantastic. Ryan ended up coming on recently, actually."
So, she was there first? "Yeah!" Stone responds with glee. Of course, Emma Watson and Whiplash star Miles Teller had originally been cast, before dropping out, though I'd lay my money on the chemistry between Stone and Gosling any day.
• Irrational Man opens on Thursday.
