linguisticsgirl.com: ... In my mind, grammatical *form**(what a word looks like) is clearly separate from grammatical function (what a word does). From ODO: 2.1. Any of the ways in which a word may be spelled, pronounced, or inflected 4.2. [count noun] A set order of words; a formula:
When Michael J. Fox played 'Johnny B. Goode' as Marty McFly in 'Back to the Future' in 1985, he was just aping Chuck Berry's classic fretwork for the camera. (Along with some Jimi Hendrix, Eddie Van Halen and Pete Townsend guitar moves thrown in for good measure.) Today, Fox can really play the song.
This scene has nothing to do with the power of love, but music fits the vibe and works in context. An early scene in the film has Marty McFly and his band The Pinheads auditioning for the high school dance. Lewis has an uncredited cameo in this scene, where he plays a teacher who is judging the auditions.