"What's wrong with the English press?" asks Viggo Mortensen.

He has just handed me a couple of his CDs - one spoken-word, one piano music (he's also an exhibited painter and photographer) - but even the generous warmup gifts can't inspire me to cover a topic so broad in a 15-minute Toronto International Film Festival interview.

As it turns out, Mortensen was talking specifically about the response to Keira Knightley's performance in the opening scenes of A Dangerous Method, which had its premiere at the Venice Film Festival a couple of days before it came to the Toronto festival (it opens in commercial cinemas on Friday). What had him fuming was early sniping by journalists about Knightley's depiction of the patient Sabrina Spielrein in the throes of what was called, at the time, "hysteria." To see Knightley, an actress associated with English Rose parts, twisting and contorting her face and body, provided easy copy for early stories out of Venice.

"She does a great job," says Mortensen. "Any other actress doing what she does would win every award possible. I thought it was a very courageous, spot-on, meticulous performance."

Once he has that off his chest, he settles down to talk about playing Freud, and an affectionate diagnosis of his director, Toronto-based David Cronenberg. This is the third film the two have made together, after A History of Violence and Eastern Promises (which earned Mortensen an Oscar nomination).

A Dangerous Method depicts the relationship between Sigmund Freud (Mortensen), his one-time protégé Carl Jung (Michael Fassbender), and Spielrein (Knightley), a Russian-Jewish patient of Jung's who later became a psychoanalyst herself (she and her family were murdered by Nazi troops during the Second World War). Since the discovery of her papers in the 1970s and 80s, she has emerged as a significant link between the two giants of psychiatry.

"When David first asked me to play Sigmund Freud," says Mortensen, "I thought, 'If I didn't know he was crazy before, I would have at that point definitely decided he was insane.' "

Despite his boyish looks, Mortensen, now 53, is the right age for Freud at the time the movie takes place. Makeup, contact lenses, a beard and a little padding make the physical transition credible. With his characteristic thoroughness, though, Mortensen also read everything he could, and visited Freud's homes in the Czech Republic, Vienna and London. As an actor who often communicates "non-verbally in my roles," he says he was particularly concerned with capturing Freud's speaking style.

"He used language as a weapon, offensively and defensively. He had a technique he employed of presenting controversial, even revolutionary ideas while including the audience, with phrases such as 'As we all know,' or 'I'm sure it's often observed ... ' so the audience would feel they shared in the idea. We worked on bringing out that contrast in Freud and Jung's speaking styles in the film - that ironic tone that Freud had, as opposed to the matter-of-fact, cold tone of Jung."

As well as praising Knightley, Mortensen is anxious that his director gets his due. "Is there any director of his calibre who hasn't been nominated for an Academy Award?" he asks at one point. With A Dangerous Method, he says, Cronenberg managed to achieve buoyancy in a film that is filled with long conversations about ideas.

"Many, even very fine, directors would have been weighed down by this subject matter and the impact these men still have on our culture," says Mortensen. "The density of the language, the formalism and detail of the era, could have made it seem ponderous. But David shot it very simply with a relatively few shots and kept a very light touch, even making it quite funny at times.

"And there was another benefit of having him as a director. When I thought about Freud, I had this ironic, erudite man with his clarity and humour, right in front of me to serve as a model."