SEX SYMBOLS.(Christina Aguilera, Justin Timberlake )

Two ideas drive much of Christina Aguilera's new double album, "Back to Basics": one is that, as she states in the first song, she wants to "understand what made the soul singers and the blues figures that inspired a higher generation, the jazz makers and the groundbreakers"; the other is a recurring assertion that she has been misunderstood, and unfairly criticized. (One response to her alleged critics is a creepy track where, putatively celebrating her fans, she replays some of their voice-mail messages. It's a long way for Aguilera to go to remind us how "amazing" and "inspiring" she is.) In the course of twenty-two songs that move from the thrilling through the well-intentioned to the overwrought, it becomes clear that Aguilera's new album doesn't have all that much to do with the "blues figures" or the "jazz makers." That's fine--Aguilera doesn't need to reincarnate Sarah Vaughan to be a serious singer. She already is one, in the tradition of nineteen-nineties pop and R. & B., skillfully deploying melisma for razzle-dazzle, riding the bouncy syncopation of samples with the coordination of a rapper, and timing the phrases to imply her athletic dance moves--or, better yet, yours.

Aguilera, a small woman with a frighteningly capable voice, debuted in 1999 with one of teen pop's happiest moments, "Genie in a Bottle," a song driven by a broadly sexual metaphor: "You gotta rub me the right way." She tweaked her assigned role of coquette by making it clear that she could whisper ecstatically, on pitch, or sing hard enough to break bulletproof glass--who cared if she writhed around in the video? The album containing "Genie" went on to sell more than eight million copies. Aguilera's second album, "Stripped," contained several tracks written with Linda Perry, originally of the dull nineties rock band 4 Non Blondes and now one of pop music's reliable hired guns. (She is responsible for some of this decade's best radio hits, including Pink's "Get the Party Started.") Aguilera's irrepressible voice brings out the schmaltz in Perry. On "Stripped," Perry's most significant contribution was "Beautiful," a barn burner for everyone who has ever felt less than cute on a Friday night. "I am beautiful, no matter what they say--words can't bring me down," goes the chorus. The way Aguilera hits the last five words--which Perry wrote as a descending line, momentarily slowing the rhythm, in a motion that pulls against the lyric's prideful claim--produced her "Rocky" moment. You know she's going to raise her fists and jump when she reaches the top of the steps, but you get goose bumps anyway.

"Back to Basics" maintains the plucky spirit of "Stripped," and the songs on the second disk were co-written with and produced by Perry. In "Back in the Day," Aguilera names some of her "groundbreakers": "Break out the Marvin Gaye, your Etta James, your Lady Day, and Coltrane." Though you can't really argue with the choices, Aguilera lists her inspirations like a teen-ager with a MySpace page linking to her favorite bands; she establishes affinities, but saying doesn't make it so. She probably does love John Coltrane and Etta James, but, aside from a few diverting period pieces--like "I Got Trouble," a sepia-toned re-creation of early Billie Holiday engineered to sound like an old 78-r.p.m. disk, and "Candyman," a tribute to a sexy man that sounds like the Andrews Sisters--there are precious few audible connections to any music predating the seventies soul of Stevie Wonder. (She does effectively evoke him several times.) For all the carrying on about history, a high-concept glamour photo shoot in the CD's photo booklet--take that, downloaders!--is Aguilera's most successful resurrection of the past.

Without a song as well written as "Beautiful," Perry and Aguilera circle the idea of sophistication to little apparent purpose and fill up the disk with sodden, obvious ballads. The ballads do, however, give Aguilera room to sing spectacularly--"Mercy on Me" is one of several examples. (She also, on "Save Me from Myself," apes Fiona Apple's quiet brand of self-torment.) It's a shame that Aguilera's voice outstrips her ambitions. She ...