"If I have seen farther than others, it is because I was standing on the shoulders of giants." scientist Sir Isaac Newton, in a letter to his colleague Robert Hooke, February 1676.

Mid-1999. Noel Gallagher is celebrating the end of recording the latest album in a London pub with a late-night lock-in and liberal quantities of Guinness. At around 4am and in a state far from sober, he notices the new £2 coin for the first time, and particularly the quote from the great British physicist Isaac Newton that circles its rim. Inspired, Noel scrawls the words on a cigarette packet. Except he is so drunk that the next day it reads "Standing On The Shoulder Of Giants" instead of shoulders, and instead of 'album title', he's written 'a bum title'. Which, Oasis being who they are, ensured it would be the name under which their fourth studio album would be released. "People said it was too long," laughs Noel. "But then they said that about 'What's the Story, Morning Glory'".

In fact, the title sums up one of his band's great talents. Only a handful of acts in the history of music get to define their generation. To know that right then, at that moment, no one is making music that is more important, that expresses more clearly the hopes and aspirations of the time. From the release of 'Definitely Maybe' in 1994 to the massive concerts at Knebworth in 1996, Oasis were indisputably that act. Since then they've started families, continued to tour the world, written 'Standing On The Shoulder Of Giants' and remained the indisputable world champions of rock'n'roll.

Spokesmen for the chemical generation, they were five lads sticking a finger up at authority and having a ball at a time when partying was out of fashion. They made music to brighten the grey Major years, and took it all the way to drinks at Downing Street and beyond: a rock'n'roll band for people who hadn't had a band of their own for a long, long time. But Oasis were also unique in that they didn't speak for the future by denying the past. Though it never sounded anything but contemporary, their music paid open tribute to the Beatles, the Sex Pistols, the Stone Roses: the three decades of British rock that had come before. Oasis have always stood on the shoulders of giants, which is why they towered above their peers.

For the band, the party started some time in 1993 and continued, pretty much non-stop, until 1997. As Noel says, "We did our share, and then we did everyone else's who couldn't afford it." But then it stopped being fun. One night, Noel remembers going to a film premiere with his wife, and deciding just for the hell of it to stay straight and sober. Sipping mineral water, he stood at the bar with the friends he'd had since moving to London, watching them do the obligatory cocaine shuffle to the loos and back. And after a couple of hours, he had a revelation. "It suddenly dawned on me that I didn't like any of them. I said to Meg, 'Are these really all our friends? Have they really been in my house? But they're wankers!'" That was two years ago. He hasn't taken any drugs since. "It's made me feel better about myself. A lot healthier. A lot more clear.

It was great at the time, but it came to the point where I just couldn't be bothered having the same conversations with the same people in the same chair in the same fucking house every week about UFOs. I got sick of waking up with a golf ball up my nose and cotton wool for a head. I look back on it as having some brilliant, brilliant laughs, but also having too many stupid conversations with people I didn't necessarily like."

Even Liam has calmed down a lot too. The irony, of course, is that 'Standing On The Shoulder of Giants' is the most psychedelic Oasis recording to date. "When I first played the likes of 'Who Feels Love' to people, they said, 'Are you sure youâve stopped taking drugs?'" laughs Noel. But it's an album more about negotiating the comedown than celebrating the highs, about self-indulgence and coming through the other side older, wiser - and ready to make a fresh start. There's even a touching, tender song written by Liam ('Little James'), although Noel denies that this means their stormy relationship is any better - or worse - than it's ever been now that fatherhood is upon them both.

It's the first time the band have worked with prolific studio whizz Mark 'Spike' Stent (U2, Madonna, Bjork, Massive Attack), and the collaboration was a fruitful one: for the first time, Noel says he was working with someone who understood club culture, who could get the sounds he'd heard on dance records and apply them to an Oasis album, For the first time too, there was someone who was able to stand up to his musical excesses, to tell him when enough guitar was enough. "He was good at stopping me from going mental in the studio."

The album was recorded in France, then reworked in England after the departure of band members Paul 'Bonehead' Arthurs and Paul 'Guigsy' McGuigan. "Musically, it's a fresh start," declares Noel. It is also, he admits, a transitional record, made mainly after the old members had left, but before their replacements had been recruited. "It goes about a third of the way to where I want to be with the band in about five years." The new line-up featuring rhythm guitarist, Gem (formerly of Heavy Stereo), and bassist Andy Bell (formerly of Ride and Hurricane #1) alongside Noel, Liam and drummer Alan White made their debut in Philadelphia in December 1999. The full world tour starts in Japan in February 2000, and covers the far east, North and South America, and Europe, hitting the UK in July for the sold out stadium shows at Wembley, Bolton, and Edinburgh. "I'm as interested as anyone to find out how it's going to be," says Noel. "The first time I looked across the stage and Bonehead and Guigs weren't there it was a bit weird. But the main difference is that it's a lot better musically, because Gem and Andy are such good musicians."

He's not sure how often Oasis will tour after this one, but Noel Gallagher is in this for the long haul. "I could happily sit in the studio forever, writing music. This album is good, but the next one will be better. And that's the way you should feel about music - I wouldn't like to record the perfect album, because then that would be it. I hear faults in every single track here, but by the same rule, I think it's probably the best album you'll hear this year. And there will be another 10 or 20 after this. There's a lot more coming."

Oasis, then. A new band. A new century. A new direction. And a fierce commitment to writing great songs and performing them with passion - which, of course, is nothing new at all.