Where does one kind of music end and another begin? How much do we invest in the distinctions between genres, when the differences between them may not be that great? Someone famously said, "There are only two kinds of music, good and bad." That the quote has been attributed to musicians as varied in their backgrounds as Duke Ellington and Richard Strauss attests to its basis in fact: Musicians make music from the language at hand. Genre has nothing to do with it.

That said, what shall we make of symphonic Led Zeppelin? The Phoenix Symphony has been hired on as the back‑up band for an event Jan. 20 called "The Music of Led Zeppelin: A Rock Symphony," to be performed at the Dodge Theatre. (For tickets, go to www.livenation.com or call (480) 784‑4444.)

Usually, when rock or contemporary pop tunes get strings added, the result is denigrated as Muzak. I've seen grown women freak out when they notice a Duran Duran song or something by Depeche Mode blurted out by stuttering violins over the elevator. "When I hear that music between floors," one told me, "I know I'm old."

What about when classic rock gets violins and French horns and timpani and oboes? Does it mean the music becomes classical?

"My concept for The Music of Led Zeppelin was to take the music as close to the originals as we could and then add some colors to enhance what Zep had done," says the event's producer‑arranger Brent Havens in a story posted at the Web site for station KSLX (www.kslx.com).

"The wonderful thing with an orchestra is that you have an entire palette to call upon. The band is reproducing what Led Zeppelin did on the albums, verbatim, and then having an orchestra behind the band gives the music a richness, a whole different feel, a whole different sense of power."

A singer–Randy Jackson of rock band Zebra–will sing Robert Plant's vocals while a band duplicates Led Zeppelin's playing "riff for riff." Havens will conduct the symphony in its "enhancement." The eighteen songs will include "Stairway to Heaven," "Heartbreaker," "Black Dog" and "Immigrant Song."

Music is music, and can translate from rock to symphonic without distortion, even if the symphonic end of things is little more than color added to an already full musical plate of melody, harmony and rhythm. If those basics are in place, the rest is a matter of sonics, not of genre.

Ask Nicole Pesce. The extravagantly gifted cocktail pianist has more than 10,000 pieces of music at her fingertips, and their variety staggers the imagination.

One night at My Florist, the downtown Phoenix café where Pesce holds her court of chords five nights a week, she started off with a bouquet of Stevie Wonder songs that slid into Henry Mancini's theme for "The Pink Panther," sidled into Rodgers and Hart's "This Can't Be Love," took a sharp turn into Warren Zevon's "Werewolves of London," and ended with a big number from the musical, "Les Miz." Somewhere in there was a song by Coldplay.

She's been known to segue from a Beatles medley to Rachmaninoff to rags to Radiohead. If a piece has melody‑harmony‑rhythm, she can play it–which means, by the way, that she can't play hip‑hop, because it lacks the harmonic structure necessary to bring it to the piano. For hip‑hop to cross genres would require the percussion section of a symphonic band. But it could be done.

Music in our time has had a lot to do with identity. People who listen to country are different from folks who listen to disco, who are different from jazz, or classical, or world music fans. Or so we're told. It has the effect of prejudicing the unwitting against a stranger, based on the music they like. An earlier belief had it that music is a universal language with the power to unite, not divide. Listening to Pesce's phantasmagoria of sound, the uniting idea would seem to hold true.

Somewhere in time is a music without labels, where a piece is either one thing or another: good or bad. But that's a distinction booby‑trapped with its own prejudices and assumptions. We'll go there another time–or not.