Prince's roaming early '80s muse couldn't be contained, even by the thrillingly complex records he was releasing under his own name. So, he began assuming other musical personas, writing songs – and, more intriguingly, creating complete demos – of tracks for other artists.

Those demos, not enough of which are collected in a new 15-song Prince Estate posthumous release simply titled Originals, underscore an almost telepathic ability to inhabit other music minds.

There's "You're My Love," a pitch-perfect Kenny Rogers song that Prince gave away to, yes, Kenny Rogers for 1986's They Don't Make Them Like They Used To. He somehow knew that Time frontman Morris Day's winking brand of sexuality, both more up-front but also safer than Prince's own, was better suited to "Jungle Love." And that Sheila E's furious percussion style – not to mention a needed dose of girl-power – would ultimately complete "The Glamorous Life." (Also that he'd have to lose a free jazz-inspired sax bit at the beginning.)

That all of this was going on behind the scenes while he was also breaking through with initial radio hits from 1982's 1999 and then breaking wide with 1984's Purple Rain might come as a surprise to some, since so much of his outside work was done under pseudonyms. But whether credited to Jamie Starr, Joey Coco or Christopher, Prince's frisky genius would not be denied.

In fact, a number of these songs – notably the muscular "Holly Rock" (which Sheila E. later covered for the Krush Groove soundtrack), the robo-funk dance number "Make-Up" (which boasts a forward-thinking transgressive feel when heard outside the context of Vanity 6's lone album) and the falsetto-sung, gospel-flavored "Baby, You're a Trip" (which Jill Jones issued as a b-side to 1988's "For Love" single) – might have easily slipped into the track listings of Prince's contemporary albums. Originals isn't always about stepping outside himself.

Some of the things he gave away (most notably "Nothing Compares 2 U," which became a No. 1 hit for Sinead O'Connor a few years later; but also Apollonia 6's "Sex Shooter," which quite frankly makes way more sense being sung by a man) are simply confounding. Others, like "Manic Monday," make a bit more sense. It might have been a perfect musical fit for 1985's Around the World in a Day, but who can really picture Prince in the very un-Prince position of working an every-day office job? A few don't quite measure up to his incredible official discography.

All of them, however, arrive as largely complete musical thoughts. Prince demos, because of his ability to play a remarkable array of instruments, don't present like other people's partially sketched out thoughts.

In fact, "Jungle Love" was largely unchanged when the Time took it to the Billboard Top 20 in 1984 – right down to a "somebody bring me a mirror" ad lib that Day brazenly claimed as his own. "Love ... Thy Will Be Done" was clearly handed off to Martika as a ready-made No. 10 1991 hit. The Bangles changed almost nothing musically on the way to making "Manic Monday" a No. 2 smash in 1986, including the sun-splashed piano asides.

Some things – like Prince's genius – just arrive fully formed. (Keep in mind that he demoed "Nothing Compares 2 U" the same week that "When Doves Cry" was topping the charts.) That we're still discovering new corners of that genius is a testament to Prince's innate musical intellect, but also to a once-unquenchable thirst for new challenges. Turns out, Prince was often just as great even when he wasn't being Prince.

So, why wasn't this a box set?

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