Oh, It Makes Me Wonder

Gradus ad Parnassum, meaning Steps to Mount Parnassus (in Greek mythology, the home of the Muses), is a famous musical composition textbook from the 18th Century. It taught, in a series of step-by-step lessons, the rules of the musical technique known as counterpoint, where several different melodies are composed to be performed in harmony with each other. Of course, once the student had mastered the rules (it was very technical), they would hopefully be able to work out for themselves where they could get away with breaking them for artistic effect.

Led Zeppelin's most famous song is called Stairway to Heaven. You know the one - starts of gently with 12-string guitars, recorders, and references to Tolkien, and gradually becomes more Hard Rock as it progresses (You can listen to it in Pete's Progcast if you wait long enough for it to come round). The resemblence between the title and that of the Baroque music textbook may seem like a complete coincidence. However, there's a bit near the end that goes

And as we wind on down the road,
Our shadows taller than our souls,
There stands the lady we all know
Who shines white light and wants to show
How everything still turns to gold.
And if you listen very hard
The dream will come to you at last
Where all are one, and one is all,
To be a rock, and not to roll!

If you're singing Stairway to Heaven on a karaoke night, about halfway though this bit you realise that you're really going to need a drink after this. Each line of the passage goes to just about the same tune, but is pitched a little bit higher than the one before. In musical terms, that's called a canon. It's a technique that was frequently in the type of music that Gradus ad Parnassum teaches,