Prince simply made use of one of the most potent and consistent techniques of his career: careful appropriation of popular trends in pop music, filtered through his unique sound.
Traditional evaluations of Purple Rain’s songs have tended to describe it as a particularly original creation, given that it includes such distinctively Prince-ly works as When Doves Cry and Darling Nikki (both of which he wrote and performed entirely by himself). But Prince was always watching closely to see what was popular around him, and he put those observations to use in creating the album.
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All of this evidence makes it clear that Prince was deliberately scouring as many different sources and influences as possible to design a rocking guitar anthem with maximum mainstream appeal.
Anil Dash on Prince's Purple Rain, 30 years' old this week:
And here's a video from the August 3, 1983 concert in which Prince introduced both the song, and his group, The Revolution, for the first time.
Peter Friedman is a lawyer, artist representative, speaker & writer who's written for years on the impact of law on creative endeavors and law itself as a creative endeavor. From 2008-2012, he wrote Ruling Imagination: Law & Creativity, selections of which are republished here and the entire archive of which is available from the Internet Archive's Wayback Machine here and in pdf format here. In addition, he has written about copyright and fair use at What is Fair Use?