Beyond the Octave
Before we move on to more theory concepts, we need to cover one last topic in the realm of intervals.
You’ve probably seen chords that refer to numbers like 9, 11 and 13 and you may be wondering how they relate to what we’ve looked at. These numbers refer to specific notes in the chord that make up its unique sound. If you guessed that these numbers are related to intervals, give yourself a pat on the back.
A ninth is simply a second moved one octave up. In chords, we typically don’t play the second with the root because they’re so close to one another and sound fairly dissonant. So by moving the second up an octave we spread the notes out making for a better-sounding chord and, usually, easier fingering.
Take a look at this diagram showing a root, a second and a ninth. Notice how the ninth is simply an octave above the second:
This is a handy thing to remember because if you know the intervals one through seven and you know your octave shapes, figuring out the extended intervals is easy.
In the case of A major, B is the second degree in the scale. If you keep counting up to the B in the next octave, you end up at note number nine, which is why it’s called a “ninth”.
The 11th is a similar idea. It’s a fourth moved up an octave:
The 13th is simply a sixth moved up an octave:
You’ll notice that in all three cases, you just need to subtract seven to get the original interval number:
9 - 7 = 2
11 –7 = 4
13 - 7 = 6
So what about tenths, twelfths and fourteenths? While these exist, you don’t really hear anyone refer to these intervals. The 9th, 11th and 13th are the only “extended” intervals you’ll hear musicians talk about. This has to do with the role these notes play in advanced chord construction—a topic we’ll get to later.
I should point out that musicians aren’t particularly strict about when they call something a ninth vs. when they call it a second. If I were showing someone this two-note shape, I would just call this a major third, not a tenth:
Confused? The general rule is that musicians will refer to 9ths, 11ths and 13ths when they’re talking about chords or arpeggios. Any other time, musicians will stick to referring to the notes by the intervals one through seven, no matter how far apart the notes are.
For now, you just need to keep these points in mind:
- A ninth is a second raised an octave
- An eleventh is a fourth raised an octave
- A thirteenth is a sixth raised an octave
- The “9/11/13” nomenclature is used generally when referring to chords and arpeggios
One last point, is that these degrees can also be altered with ♯ or ♭ designations. A ♭9 is the same as a ♭2, but raised on octave.
Until next time, keep rocking!