A fundamental concept of music theory is the idea of intervals.
An interval is the musical distance (or difference) between two notes.
On guitar, you can think of it as how many frets there are between two notes.
Think About Musical Intervals on Guitar
When it comes to beginners thinking about intervals, the guitar gives us a problem:
We have a lot of strings
This can make it difficult to visualise intervals, especially when working them out across strings.
So, to get started with the basic concept, let’s pretend that our guitar has a single string.
Intervals on a single string
Think of an interval as an amount of frets, or, as a distance along the string that is measured in frets.
Each amount of frets has a special name.
If we were to take any note on guitar, then play the note that is one fret higher up along the string, we would create an interval of a minor second.
If we were to take any note on guitar, then play the note that is two frets higher up along the string, we would create an interval of a major second.
When we are looking at intervals, the note we start from is always called the “root note”.
If we take any note on guitar, and move up the string by the following amount of frets, we create the following intervals:
- Minor Second / Flat Second (b2)
- Major Second (∆2)
- Minor Third / Flat Third (b3)
- Major Third (∆3)
- Perfect Fourth (P4)
- Sharp Fourth (#4) / Diminished Fifth (b5)
- Perfect Fifth (P5)
- Augmented Fifth (#5) / Flat Sixth (b6)
- Major Sixth (∆6)
- Flat Seventh (b7)
- Major Seventh (∆7)
- Root / Octave (R)
Note that when we are 12 frets from the root note, we get the same note. I.e. 12 frets up from the note A, we get the note A. If we start with the note C and go down 12 frets, we get the note C again.
Which Interval is the “Right One”?
You can see that some of the intervals have two possible names. For example, a distance of 6 frets can be called a #4 or a b5.
There is a “right” answer, depending on the context. If you listen to the Lydian Mode being played(Steve Vai), you will hear a #4, if you listen to a diminished chord being played (some Yngwie arpeggios), you will hear a b5. The interval we hear is context dependent.
Intervals Are Direction Dependent
It’s worth noting that the interval of a distance depends on the direction we are moving in. For the physicists, we can think of intervals as being a vector, not scalar.
Look at the following diagrams:
We have the same distance in terms of frets, but depending on where we start counting from (where we place the root note), we get a different interval.
To further complicate things, we could think of a b6 as being a ∆3 lower than the root note!
You can use the above list in Intervals on a Single String to help you work this out. If the root note is the higher note, start at the 12th item in the list and work backwards, to help you figure out the interval.
Working Intervals Across Strings
This is a little bit more complicated, but a necessary step. After all, our guitar has multiple strings, not one theoretical string!
Visualising intervals in the mind is easier on a 1D string, rather than as a 2D grid (our guitar).
If we took all the notes G on the guitar, and lined them up by pitch, we could compare the strings against a single, imaginary, super long string like this:
I sometimes find this helps place the intervals relative to each other in my mind better, than seeing all the notes at the same time like this:
Tones and Semi-Tones
Measuring intervals in terms of frets is a good way to get started, but will be confusing if talking to a musician that doesn’t play guitar.
Musicians measure intervals in terms of tones and semi-tones. You can think of a tone as being the difference in pitch of two frets, and a semi-tone as being a difference in pitch of one fret.