There are only two octave shapes that form the foundation of countless chords and scales across the entire guitar fretboard!
What Do I Mean by That?
Let’s start with a quick interactive challenge. Imagine you begin with a C note on any low string. Can you find all other C notes that are:
- One octave higher
- Within 4 frets of the starting note
You’ll find that regardless of the starting position, you can only reach one or two other C notes that fulfill both conditions. Below is a visual summary showing all the reachable octave positions for C notes on lower strings (up to the 12th fret):
The Two Core Octave Shapes
If you followed along, you’ve just used two fundamental octave shapes to navigate the fretboard and locate the same note in different octaves. These two shapes can be summarized as:
- Shape 1: Next octave on a higher string and higher fret
- Shape 2: Next octave on a higher string but lower fret
However, due to the tuning difference between the 2nd (B) and 3rd (G) strings, these shapes shift slightly when crossing that boundary.
Here’s a table that maps how each root note on the lower strings leads to its next reachable octave using Shape 1 or Shape 2, accounting for tuning offsets:
| Root Note String | Shape | Next Octave Cross G&B String? | Next Octave String | Next Octave Fret |
|---|---|---|---|---|
| 6 | 1 | No | 3 | -3 |
| 5 | 1 | Yes | 2 | -2 |
| 4 | 1 | Yes | 1 | -2 |
| 6 | 2 | No | 4 | +2 |
| 5 | 2 | No | 3 | +2 |
| 4 | 2 | Yes | 2 | +3 |
| 3 | 2 | Yes | 1 | +3 |
Why Limit the Search to 4 Frets?
In the earlier game, we restricted the search to notes within 4 frets (either up or down) of the root. This isn’t arbitrary—it’s based on ergonomics and practicality:
- Most chord shapes span no more than 3 frets
- Most scale shapes span up to 4 frets per string
- Anything beyond that often requires shifting hand position, which breaks continuity
Put simply: what you can reach without moving defines how you play. These two octave shapes lie at the core of what is physically playable on the guitar.
Further Extending The Two Shapes
You may have noticed that for a root on the 6th string, you can find the roots in the next two octaves by stacking Shape 1 and Shape 2 alternately. Shape 1 moves toward higher frets, while Shape 2 moves backward. By combining these two, you can identify roots (roughly) in the same position across octaves.
If we extend this idea to an 8-string guitar, we could potentially find a position with three full octaves using alternating Shape 1 and Shape 2. On a standard 6-string guitar, even if you “run out of strings” while searching for the next or previous octave, the interval relationship still exists conceptually. We’ll explore this idea further in the next post.
What’s Next?
In the next posts, we’ll explore how these two simple octave shapes form the foundation of the CAGED interval system:
- How the two “reachable” octave shapes build the CAGED forms
- How to evolve the octave shapes into full scales, arpeggios, and chords
- How to use these shapes to think about parallel modulation and tonal shifts
Stay tuned!