NEW YORK – The latest presentation of the On Truth (and Lies) conversation series of the Onassis Foundation (USA), which always takes place on a stage, delighted the audience at the Morgan Library in Manhattan with its alternation between and philosophical discussion and theatricality.

Renowned actress Fiona Shaw would make a fine professor, but there were also powerful moments of drama and comedy in her conversation with Simon Critchley for “On Truth (and Lies) in Acting” on January 15.

Critchley, who is also the series moderator for The Stone, writes a popular online philosophy column for the New York Times. He was born in England and is Hans Jonas Professor of philosophy at the New School for Social Research.

Shaw is an Irish actress and theatre and opera director. She is best known as Petunia Dursley in the Harry Potter and Marnie Stonebrook in the HBO series True Blood, but she is also an accomplished classical actress, having worked extensively with the Royal Shakespeare Company and the National Theatre.

Shaw’s subtle but powerful gifts transported the large audience on Jan. 15 to the ancient theater of Epidaurus, into the lines of Euripides’s Electra the plays of Shakespeare, and Samuel Becket’s Happy days, and to the stage of the Metropolitan Opera and its recent productions of Russian opera.

Seated before the audience and a small table with a vase filled with yellow flowers provided by the hospitable hosts of the Onassis foundation, Critchley himself alternated between moderator to member of the audience during Shaw’s passionate responses to his well-posed questions on the theatrical experience.

They held the audience’s rapt attention, sometimes grabbing them with their seriousness and intensity, and at other times with their playfulness and humor.

Shaw’s responses drew upon scenes from her childhood in Ireland and her current encounters in theater, including exchanges with her backstage mirrors.

She charmed the audience with the story of how she discovered the power of rhythm and meter – poetry – as a child. The audience laughed when she described sitting at a table doing her math exercises while mother was playing a song on the piano.

Her mother would play a passage – and stop. And then another passage – and she stopped again. Shaw found that the pace and pattern of her math work exactly matched the tempo and breaks of her mother’s music.

She then informed them that when she looks at her mirror today, she is no longer interested in becoming a different person, although that was not the case when she began acting.

She told a humorous story of an early audition – and then paused dramatically, saying that she still cannot believe the impact on her of the characters who inhabit her.

Now that she is also directing, she is gaining completely new insights.

Last year when her friend Deborah Warner was unable to direct Peter Ilyich Tchaikovsky’s Eugene Onegin at the Metropolitan Opera, Shaw took her place.

When she was giving direction to a Russian actress, the latter panicked and shouted “What are you asking me to do?” But when she did what Shaw wanted, she was fine.

The Morgan Library audience burst out laughing when Shaw said she asked herself at the time: “Is this what I do?”

Critchley said there are ghosts in the theater, and then asked Shaw her thoughts about time in the theater, playing roles from Shakespeare 500 years ago and from Aeschylus 2,500 years ago. He asked her to what degree performing their plays makes one feel that the present is confronting the past and even communicating with the dead.

She said however clear an actor becomes regarding time in theater; every performance is different, mainly because there is always a different audience.

Then she magically conveyed herself and the audience to the spiritual space of Epidaurus, “the most wonderful theater in the world…with its 12,000 seats and 7000 people in the audience.”

She was performing Becket’s “Happy Days” a few summers ago and in a twinkling “I saw the audience’s jeans turn into togas,” she said, as she laughed with the audience.

The lively conversation on the art of acting seized the minds and hearts of the audience and Shaw welcomed their comments during the Q&A which followed because she knew they were coming from New York’s theater lovers.

Indeed their questions extended the conversation. Critchley was taken aback when he realized during one of the questions that he did not ask Shaw for her take on Aristotle’s concept of Catharsis. “Oh for God’s sake,” he blurted out.

Critchley took that opportunity to spell out Aristotle’s definition of tragedy and explain his ideas about catharsis, which the audience appreciated.

The young lady who asked the question recalled seeing a play during a very difficult time in her life “but when I left the theater I felt liberated. Is that catharsis,” she asked.

Shaw then told of once playing Electra, and described her wrenching monologue mourning her brother. It was during the time she was mourning the death of her own brother and the said that by interpreting Electra’s pain, she was able to mourn her loss.

Then Petunia seemed to burst onto the stage and say “We need more dramaturgy in our lives, not just entertainment. When you go to see something for your amusement, you leave the theater exactly the way you went in.”

But it tragedy, as Aristotle wrote in his Poetics, one identifies with the heroes that are portrayed onstage and people are changed. The audience members leave with insights and are purged of unhealthy emotions like fear and pity and they emerge more mature and stronger.