The imperial phase is that period in an artist's career when everything's completely brilliant.
The imperial phase of someone's career is a bit like an amazing post-chorus in an amazing song: you think you've got the general idea of what's happening, but then things shift up a gear and become truly immense.
About 25 years ago, when Neil Tennant coined the term, he reckoned that Pet Shop Boys' own imperial phase ran from June 1987 to April 1988. Less than a year, but ten months in which the band scored three Number One singles and released 'Actually', a 4m-selling album.
Unusually, given that most artists refuse to admit (or admit they've admitted) when things start to wobble, Neil also acknowledged the point when the band's imperial phase was over: a few months later, when the first single from the band's next album, 'Introspective', missed the Top 5. 'Introspective' was brilliant, the album after that was better than 'Actually' and the album after that gave Pet Shop Boys their first ever UK Number One, but the imperial phase was long gone.
There's nothing quite like the thrill of seeing an act enter its imperial phase: that period in their career when somehow, through luck or judgement or a hefty amount of both, they just get everything right, and the world reacts accordingly.
We're talking about Lady Gaga during the 'Fame Monster', Girls Aloud's 'Chemistry' winning streak, Madonna for an unusually long stretch of the 1980s, that sort of thing.
2014's imperial acts
Last year two acts — Ed Sheeran and Taylor Swift — entered their respective imperial phases. You could say Sia and Beyoncé both touched on it too, but Taylor and Ed really romped through the year in the most spectacular fashion.
Ed and Taylor were mates with each other. They both released singles in the summer and albums in the winter. They both embraced digital album release campaigns in an effortless and reflexive way; one supported streaming and broke Wembley Stadium's ticket sales record while the other gave streaming a swerve and broke US album sales records.
They presumably both had high hopes for their new albums. But nobody could have predicted quite how well things eventually went. Tellingly, neither of these two superstars appeared from nowhere — they were already world famous, platinum-selling artists at the beginning of 2014.
And that's the thing with imperial phases: they tend not to happen during an act's first album campaign. There's a sense of momentum to to an imperial phase. Most artists hope to release albums that give them a step up; when an act is in its imperial phase, their album release is more like an entire staircase.
2015's imperial artists?
The exciting thing about the need for momentum is that while there'll surely be some exciting new arrivals over the next twelve months, any artist entering their imperial phase in 2015 will probably not be a fresh act we haven't heard of.
It'll be an act that's already walking among us. We might already think they're pretty great — just like we thought Taylor Swift was pretty great at the start of 2014 — but we have no idea how great they're going to become.
This act might already have recorded the album that'll be the centrepiece of their imperial phase. Most importantly, they've probably already recorded the single that'll kickstart the whole thing.
Maybe, while they were recording that music and hatching their first ideas about how to promote it, or what the artwork would look like, or what should happen in the first video, the artist found that the decisions were incredibly and quite surprisingly easy to make. They found that the creativity was flowing in an unusually free way. Maybe they didn't remember things being so easy last time, or the time before. Something, they maybe thought, had changed.
When an act's in its imperial phase they make everything look incredibly easy, and a lot of the time that's because the planets have aligned and everything somehow is genuinely easy.
The popstar has have achieved a higher sense of pop consciousness.
They are Neo.
So who could get everything right in 2015?
Well it won't be a Cheryl or a Britney or a Gwen Stefani or a Madonna or any of that lot.
In creative terms Charli XCX is probably in the right kind of zone at the moment, but 'Sucker' doesn't represent a true imperial phase and her next album's not likely to come until 2016, so it won't be her either. Marina looked like she had the potential to enter an imperial phase, but we're not convinced the 'FROOT' campaign to date has laid appropriately robust foundations.
So. Lorde could do it, Sky Ferreira could do it. Adele, Emeli Sandé, Ellie Goulding, Leona; they could each do it. Could an FKA Twigs or a Grimes pull something out of the hat? If Ed Sheeran proved anything in 2014 it was that you can never quite predict which popstars are on the verge of being brilliant.