The Notorious (and Legally Problematic) Intro
Yes, the intro is very similar to a part of Spirit’s instrumental song Taurus. But now that the Supreme Court has judged that Led Zeppelin are the rightful owners of the riff, we can all rest assured that the intro is theirs and theirs alone. The truth is, Zep (as they’re commonly referred to by fans) was the opening act for Spirit during their first US tour (1968-69), where the song was a regular part of their set.
Source: Flickr
This guitar intro has been often parodied, but there’s a reason why it’s remained a classic. It provides a perfect example of a musical concept called contrary motion, where voices move in opposite directions. In the intro, the lowest sound on the guitar goes down from A to G sharp to G, while the higher sound ascends from A to B to C. And then the pattern is broken.