EASY GUIDE

They’re the most basic intervals of all… but how do they work? And why do they contain twelve notes? Dave Clews explains all

Dave Clews explores the ins and outs of the octave

In this month’s Easy Guide, I’m looking at one of the most compelling mysteries you come across when exploring music theory for the first time: what is an octave, and why are they called octaves when they contain twelve notes? OK, that’s two mysteries, but to address one means addressing the other, so let’s start picking at the thread and see where it leads.

It’s become a sort of unofficial Easy Guide tradition to start off with a diagram of a C major scale, largely because an understanding of how a scale is formed is integral to so many other aspects of music theory. An explanation of octaves is no different, but what you’ll have noticed if you’re a regular reader (and why wouldn’t you be?) is that sometimes I’ve described the scale as having seven notes, other times as having eight notes, depending on the topic. The main difference is that, technically, there are seven note pitches in the scale –C D E F G A B – but if you add the repeated scale tone that’s one octave higher than the root, you end up with eight notes: CD E F G A B C. Those two Cs are eight scale tones apart, which is where the octave gets its name – most of the important scales are written with eight notes. Music theory is full of this kind of thing, like how an interval of seven semitones is called a perfect fifth. But I digress! Let’s delve deeper into the origin of the octave.