Intervals in Music
An interval is the distance between any two notes. There is a standard way of naming all the distances from one note to another.
The notes can be stacked up, as in a chord, or played one after another, as in a melody.
We’ll continue using the key of C major (starts on the note C, no sharps and flats) as our basis, but these rules apply no matter what key you’re in.
If the two notes are the exact same note, the interval is called unison. If they are the same letter name but in different registers (for example, a low C and a high C), then the interval is some number of octaves.
After this, we use numbers to identify the distance of the interval. From C to D is a second, from C to E is a third, etc. Usually you don’t go higher than a thirteenth, and in this article we’ll just talk about the intervals from unison up to the first octave.
Besides the distance, we also need to specify the quality of the distance. Here is a chart in C major:
| C - C | unison |
| C - D | major second |
| C - E | major third |
| C - F | perfect fourth |
| C - G | perfect fifth |
| C - A | major sixth |
| C - B | major seventh |
The fourth and fifth in a major scale are always called "perfect." (For that matter, unison and octave are also "perfect" intervals.)
If you make a major interval smaller by a half step, it becomes a minor interval. C - Db is a minor second. C# - E is a minor third.
If you make a perfect interval or a minor interval smaller by a half step, it becomes a diminished interval. From C to Gb is a diminished fifth.
If you make a major interval larger by a half-step, it becomes an augmented interval. From C to F# is an augmented fourth.
Now you may have noticed something interesting. The same interval can have multiple names. From C to E# is an augmented third; from C to Fb is a diminished fourth.
Once again, it comes down to the function in the key you’re in and in the song you are playing. For example, the flatted fifth (another name for a diminished fifth) is a very distinctive sound in a blues song. If you’re playing a bluesy song and you have that interval, it would be referred to as a flatted fifth, not an augmented fourth.
On the other hand, the intro to Purple Haze by Jimi Hendrix is often described as being augmented fourths…so it comes down to convention and partly some personal opinion when describing intervals.
In general, you need a good reason to call an interval, say, an augmented second rather than a minor third, or a diminished sixth rather than a perfect fifth.
Intervals can also be specified by how many steps/helf-steps between the two notes:
| half-step | minor second |
| whole step | major second |
| three half-steps | minor third |
| two whole steps | major third |
| two whole steps plus a half step | perfect fourth |
| three whole steps | augmented fourth, diminished fifth |
| three whole steps plus a half step | perfect fifth |
| four whole steps | minor sixth |
| four whole steps plus a half step | major sixth |
| five whole steps | minor seventh |
| five whole steps plus a half step | major seventh |
| six whole steps | perfect octave |
Using that chart, you can tell the interval between any two notes, not just combinations starting with C. For example, from F to A is a major third, from E to C is a minor sixth. There is an easier way to do it as you learn what sharps and flats are in any key. That will be discussed in a future article.