Small wonder, then, that her buoyant, boisterous but incontestably musical choreography has used everything from Haydn, Telemann and Rossini to Bix Beiderbecke, David Byrne and the Beach Boys. Her all-new company, opening tonight at the Edinburgh Festival, will dance to early American religious choral music, bachelor-pad lounge music and Philip Glass's arrangement of David Bowie and Brian Eno's "Heroes".
Despite all that, she's unwilling to define herself, as Mark Morris has done, as a musician. "People use language and labels in different ways. I don't assume a great deal. I think you work hard for those labels and you don't give them to yourself either." This is the Tharp of legend. Interviews are rare and quite obviously not her favourite activity. In contrast to her fleet, fresh and frankly exhilarating work, in person she's alert, austere and stern. You don't get to where she is without high standards, standards she clearly expects from others, whether they be dancers or journalists.
She auditioned across the USA and Europe to field her new, young, 11- strong company, which includes ex-London Contemporary Dance student Andrew Robinson. For all their manifest technical skills, her company is not made up of uniform, perfect dancing machines, so I ask her if she thinks there is such a thing as a Tharp dancer. Leaning forward, she immediately bats the question back at me, her dark, piercing eyes blinking over her owlish horn-rims. I suggest that there is. "Who, and what?" she demands. Taking my life in my hands, I talk about her distinctive use of body weight, citing Robinson as someone who combines that with an innate sense of attack to communicate a huge emotional range when moving from rest to a new position. There's a pause, during which I wish I'd stuck to being a dustman, and then the ice breaks. "I don't disagree with that," she says and, suddenly, we're off.
She's not fierce, just feisty, a quality that obviously saw her through what must having been an exhaustingly musical childhood during which she also found time to study ballet, modern dance, jazz, show-dancing, tap and baton-twirling. She came of age more than 30 years ago at the height of the New York avant-garde scene where every rule was there to be broken. Back then, there was a seismic rift between ballet and modern dance. On one side of the fence, Balanchine had reinvigorated the classical vocabulary; on the other, towering figures like Merce Cunningham had redefined structure and thrown out meaning and music. This was an era of almost medieval artistic piety. She once said, "The last thing I wanted to do on the face of this earth was to entertain. I was an artist... they do what they believe in." Looking back on it, she points to the defensiveness of that position. "It was about where I was as a beginner... not wanting it to seem as though we were trying in any way to be appealing, heaven forfend! It was part of the art climate of the time, very aggressive, very challenging."
The last 30 years have been spent redefining her philosophy and, possibly to the horror of her younger self, her work is now massively popular. The Catherine Wheel, her 1981 collaboration with David Byrne, went to Broadway; she choreographed the films of Hair, Ragtime and Amadeus; queues went round the block for her triumphant 1983 season at Sadler's Wells and critics ran out of superlatives. The key moment, however, occurred when Mikhail Baryshnikov, for whom she created the stylistic tour de force Push Comes to Shove, invited her to become associate director of American Ballet Theatre. From there she worked with everyone from the Joffrey to the Paris Opera Ballet, from the Martha Graham Company to the Royal Ballet, for whom she created her debut piece, Mr Worldly-Wise.
Her mix of styles - her attempt to arrange a marriage between classical and modern - has led certain commentators to describe her work as post- modern, a term which, in her case, I suggest, is deeply meaningless. "I like that," she beams. "Post-modernism gets itself in all kinds of tangles and knots because its basic assumption is that it follows something, it's not primary or fundamental. There are pieces in my repertory which I consider very definitely fundamental, such as The Fugue and In the Upper Room. Baker's Dozen or Sweet Fields aren't post-modern at all, they could exist without any antecedents, in the sense that they are not dependent on references. That's not to say that I don't sometimes appreciate the values of references because they help people know where they're at, but I'm interested in first causes. Sometimes they can be shorthand, but for the most part it's not what I call my mandate, my primary calling."
Calling - that's an important word for Tharp. In the course of a workshop convened to announce her new company, she created a suspensed movement and, grinning ruefully, commented that "we attempt to hang between the stars and the centre of the earth". From someone less articulate, it would sound pretentious but in fact it strikes at the depth of her approach.
"I see what I do as a devotion, as a faith, as a ritual. I always have. Before I was making dance I was doing rituals as a kid. I arranged things. Literally. I arranged rocks on the ground. I'd make rows of dirt this way or that, creating ritual patterns." For her, movement and dance have always been a religious place. "Even in the most so-called primitive societies, it's acknowledged as a way in which the body can connect through its material casing to other components. So many art forms and so much of our society would like to try to ignore that material casing." The argument is impassioned, the case persuasive. It certainly explains why the adherents of the critic Walter Pater persist in regarding music, the least human art form, as the condition to which all arts aspire. She wholeheartedly agrees that, while music is hard to write about, dance is tougher - because there's no shared language. But she adds a clincher to her argument. "Dance reminds us that time stops. And when time stops we die. We don't want to hear about this."
The 19th-century American novelist Herman Melville turns out to be one of the most cogent witnesses for her defence, in Moby Dick of all places. "He approaches movement philosophically. He sees it as a part of theology, a part of cosmology. Not of language, or words. Which it is." So, to use one of her favourite terms, does she "fundamentally" believe that movement must precede music? Her conviction rings out. "It's what I believe because it's actually the truth. Before any sound is made you gotta move. Movement is the primary action. It precedes any of the other materials from which art is created, whether it be sound, colour or language. In many ways, movement is the most common of all the denominators: the fact that we all gotta get up. That's what we have commonly between us."
Her intellectual rigour and the depth of her research - she read around 40 Balzac novels before creating Mr Worldly-Wise - might suggest a dauntingly astringent aesthetic. If the punch-drunk zest of past-masterpieces like The Catherine Wheel, the wit and drop-dead glamour of Nine Sinatra Songs or the sheer visceral and emotional thrill of In the Upper Room are anything to go by, the three new pieces will be quite the reverse.
The only bad news is that she will not be dancing. Her trademark dynamism is undiminished and she does barre exercises with the company every day but the grey hair betrays the length of her career. "Surely you jest!" she exclaims. Without wishing to be Pollyanna-ish, I murmur that stepping beyond performing could be... "Liberating? Forget it." She does, however, concede that it has forced a rethink. She feels she has moved beyond the welding of the classical and "vernacular" techniques. Something new had to happen. "Otherwise all that's really been created is a hybrid and a hybrid doesn't really move on. Look at Matisse. All those stylistic developments over his career and then he made those cut-outs. They are his most primitive work, and the most fundamental and the most sophisticated. That's the challenge: the most fundamental and sophisticated."
The crucial difference is that Matisse created those works at the end of his career. In Tharp's case, it's a new beginning. Did she see it coming? "In a sense it's why I started working," she says, laughing with pleasure. "If one has any kind of historical perspective and any kind of ambition one does aspire to coming into one's total maturity and one's potentiality. So you're willing to delay and in effect turn the early part of a career into an apprenticeship to make sure you're learning all the lessons, not just a few." Some apprenticeship. Some future.
`Tharp! New works by Twyla Tharp': tonight to Wed, 7.30pm Edinburgh Playhouse. Booking: 0131-473 2000