Starting next month, Toronto's Harbourfront Centre will be bringing 14 outstanding artists to town in a bid to celebrate great cultural talent. But ever since the arts centre by the lake unveiled World Leaders: A Festival of Creative Genius, a doubt has nagged at me. Would you call Lily Tomlin a genius?

It's not that I'm denigrating her evident talent, just that the elevation of a popular comic to the lofty heights of intellectual achievement encapsulated in the word genius crystallized the question for me. I could just as easily ask if theatre director Robert Lepage and musician Peter Gabriel make the grade. The notoriously egocentric Joni Mitchell reportedly thinks she's a genius, but what is in her songs, or her being, that makes the description apt? Are Frank Gehry and Issey Miyake geniuses because the buildings of the one and the fashions of the other look like nothing any other designer has ever created? Is the great body of black music overseen by producer and composer Quincy Jones comparable to Einstein's theory of relativity? What is genius anyway?

Psychologists used to believe it was a scientifically measurable thing. In the 19th century, Sir Francis Galton, cousin of Charles Darwin, argued that great intelligence was demonstrably genetic, summarizing his view in the title of his 1869 book, Hereditary Genius. The American Lewis M. Terman codified the modern IQ test in 1916 and suggested that a score over 140 indicated a potential genius, at which level about one in every 250 citizens could qualify.

IQ tests are still widely administered -- to join Mensa, the club for the brainy, you need to prove you are in the top 3 per cent of performers on a certified intelligence test -- but also widely questioned. It is all but impossible to filter out cultural factors from these tests, modern education theorists point out.

Attempts to quantify genius are always weighing nurture versus nature and tend to get bogged down in the politics of their time: Unfortunately, Galton is also the man who coined the term eugenics for the practice of discriminatory breeding for desirable characteristics, while contemporary discussions of remarkable intelligence toss around the hot potatoes of gender and race.

The Romantics, on the other hand, believed genius was mysteriously immeasurable. Defining it as something closer to the original meaning of the word as a person's spirit or essence, these 18th- and early 19th-century thinkers saw a flame burning in great artists and scientists that the rest of humanity simply lacked.

This vision of genius is not a question of degrees -- I score 110 but you score 145 -- but of kind: Geniuses are just different. That's why they are allowed -- and even expected -- to behave differently, taking multiple lovers, peeing into the fireplace or never wearing socks. It is also probably why women, through history only rarely encouraged to test limits the way men do, have seldom been identified as geniuses: Harbourfront's gang of 14 includes only three; Tomlin, Mitchell and choreographer Pina Bausch. The romantic approach identifies geniuses by their actual achievements not their abstract intelligence, and celebrates them with a fervour that can feel like hero worship.

So, genetic wonder or inflamed madman: No wonder the public sometimes betrays mixed feelings about the towering figure whom we call genius.

"Canadians are appalling at appreciating individual creators. We dislike people who are successful," Harbourfront director Bill Boyle has said about his project, but he is only echoing here the tall-poppy complaint that has been heard in many times and places.

"The public is wonderfully tolerant," Oscar Wilde once said. "It forgives everything except genius."

Harbourfront's theory of genius definitely follows in the romantic tradition, celebrating the great accomplishments of the famous life. It's an optimistic approach, summarized by the idea that these artists, rather than politicians or businessmen, are the "world leaders," and it tends most of all to praise them for original thought. The final selection, which Boyle and his staff pared down from long lists of suggestions, is dedicated to innovators. Gabriel invented the concept of world music; Bausch reinvented the beautiful ballet as the emotional dance-theatre; Gehry is postmodern architecture; Cirque du Soleil creator Guy Laliberté ushered the circus into the mainstream.

In the age of celebrity, some skepticism about artists' fame is refreshing, but in an era of dumbing down, the rarity of these figures' artistic vision is also inspiring. Harbourfront's programs -- a big and expensive evening of homage for each artist as well as various cheaper panels, screenings, performances and exhibitions -- will not merely celebrate the artists but also probe the source of their talent.

Bringing our fascination and our doubts to the table, we can ask a Pinter, a Bertolucci or a Rauschenberg, just how is it that you come to be so spectacularly different from us?