THE CRITICS: ROCK & POP: Whinge on, Alanis

Alanis Morissette and Celine Dion have much more in common than their unusually long chins. Both women are Canadian. Both have sold unimaginable numbers of records: Celine has shifted 100 million albums, while Morissette lags behind with 38 million. And both, though still young, are show-business veterans. Dion, 31, signed up with her current manager when she was just 12 years old. Morissette, 25, was a sitcom star at the age of 10. With cvs like that, it's no wonder that both women have a skewed perception of the relationship between life and art.

The press coverage of Morissette's 1995 album, Jagged Little Pill, focused less on the music than on the unblushingly frank disclosures of anger and resentment in the lyrics. I don't know if Morissette has read too much of her own press, but she seemed to believe, when recording a follow- up, that pouring out an avalanche of feelings was enough - never mind that on Jagged Little Pill the emotional rubble had been sculpted into jagged little shards. And so, last year's Supposed Former Infatuation Junkie is as clumsily wordy as its title. The lyrics pile up without rhyme, reason or scansion and the resultant confusion of Oprah and operatics makes a confessional newspaper column seem like a sonnet.

As Truman Capote said of Jack Kerouac, that's not writing, it's typing. And as he would have said if he'd seen Morissette in concert, that's not performing, it's sloping to one side of the stage and then trudging back again, as wearily as if she were weighed down by the hair that hangs all the way down her back. Sometimes, for variety's sake, she clumped backwards instead, which might explain why her band stayed safely in the dimly-lit rear of the stage. More likely, though, they were just embarrassed by the plodding racket they made.

On record and on stage, Morissette relies on your being charmed by her floppy, bohemian cuteness, a contingency which was less remote when she was a righteous avenger with songs like daggers than it is now that she has abandoned songs for egotistical Californian psycho-gush.

If Morissette's music is all feelings and no artifice, Celine Dion's is the opposite. Whether she is furrowing her brow, gazing pleadingly or smiling dreamily, the expressions on the video screens above the heart- shaped stage on Tuesday were those of a TV-movie actress. Her window-rattling vocals, too, tick off all the techniques of hammy emoting: the coloraturas, the pause before a song's final phrase, the transposition of the last verse up a tone. Dion hits every high note, but she always strikes a false note.

Her performance is unbelievable. Not unbelievably good or bad ... just not believable. When she nudges the pony-tailed keyboard player or the pony-tailed bassist it seems as spontaneous and fun as a state funeral; when she strokes her sparkly white trousers on "Declaration Of Love", it's as sexy as a toothbrush. Celine Dion, you're thinking, makes Bob Monkhouse seem sincere; but then a more terrifying truth dawns. As far as she is concerned, this is sincerity.

A few songs into the concert, she announced in her French-Canadian accent that she wanted to speak "personally" to all 50,000 of us. "Rene is doin' fine," she said. She meant Rene Angelil, her husband, who is recovering from skin-cancer surgery. He is also the man, 26 years her senior, who began managing her when she was 12. "I didn't want to leave him," said Dion. "But I wanted to be here tonight to thank you for all your prayers and positive energy." She then revealed that thanks to "a little technical magic", the show was being beamed across to Angelil in Florida. "He is right here with us."

Later, she concludes a special song for her husband with a wink and a nose-rubbing gesture at the camera, and you have to wonder if it's for our benefit or for Angelil's ... or if she doesn't see the distinction. Is bawling in a stadium no different to her than chatting to Rene on the sofa? The issue came into focus when the Bee Gees appeared on the video screens to harmonise on "Immortality", as Barbra Streisand had done a few songs earlier. "It's great to be here, Celine," said one of the brothers Gibb. "How's the show going?" Dion replied that it was going well and thanked them for writing the song for her. The brothers nodded modestly.

Well, sort of. The men Dion was chatting to were not actually in the stadium and they weren't linked to it by satellite. Their contribution was pre-recorded. And Dion sounded just as sincere when she spoke to these video images as she did when she spoke of Angelil.

In Dion's mind, cheesy cabaret banter seems to be the same as heart- to-heart discussions of her husband's health. Talking to her spouse is the same as talking to the virtual Bee Gees, which is the same as talking to the thousands of people who have paid pounds 50 a ticket to watch her. She's been blasting out schlocky, schmaltzy show-stoppers non-stop since she was a girl, guided by a manager who married her, so maybe she doesn't know any better.

Perhaps all great pop stars put their feelings in song, but a filtering artistry is always there. It has to be. If you transcribed an intimate tete-a-tete with your loved one, you wouldn't have a lyric. Conversely, if you promised eternal devotion to your loved one using nothing but a lyric, they'd assume you were mad.

There's the rub. Dion thinks entertainment is the same as conversation; Morissette thinks conversation is the same as entertainment. Dion thinks her public life is her private life; Morissette thinks her private life is her public life. Maybe if these two women made a record together ... no, actually it doesn't bear thinking about, but it would sell a billion copies and it would be called Let's Talk About Unabashedly Tumultuous Colonic Spiritualisation. The moral of the story: don't put your daughters on the stage, Mrs Morissette and Mrs Dion. They may never get off it.

Alanis Morissette: Wembley Arena (0181 900 1234), Wed & Thurs. Celine Dion: Wembley Stadium (0181 900 1234), tonight