Course contents Lesson 14 of 19
Interval Inversion
What happens when you flip an interval upside down, and the rules that govern it.
An interval is the distance between two notes. When you invert an interval, you flip it over: the note that was on the bottom moves to the top, so the two notes swap places. This one small move reveals a tidy pattern that makes analysis and reading much faster.
How to invert an interval
To invert an interval, move the lower note up an octave (or move the upper note down an octave). Either way, the pitch that used to be underneath is now on top. For example, C up to E is a major third. Raise that C by an octave and you now have E up to C, which is a minor sixth. Same two letter names, flipped position, new interval.
Rule one: the numbers add up to 9
Whatever the interval number is, its inversion always adds up to 9. A third inverts to a sixth (3 + 6 = 9), a second to a seventh, a fourth to a fifth, and so on. A unison and an octave are the special pair: they invert into each other.
Rule two: the quality flips
The quality of the interval changes in a predictable way:
- Major inverts to minor, and minor inverts to major.
- Augmented inverts to diminished, and diminished to augmented.
- Perfect stays perfect.
So a major third inverts to a minor sixth, a minor second inverts to a major seventh, and a perfect fifth inverts to a perfect fourth (still perfect, just a smaller number).
A quick reference table
| Interval | Inverts to |
|---|---|
| Perfect unison | Perfect octave |
| Minor second | Major seventh |
| Major second | Minor seventh |
| Minor third | Major sixth |
| Major third | Minor sixth |
| Perfect fourth | Perfect fifth |
| Perfect fifth | Perfect fourth |
| Minor sixth | Major third |
| Major sixth | Minor third |
| Minor seventh | Major second |
| Major seventh | Minor second |
Why it is useful
Inversion simplifies both analysis and voice leading. When two voices cross or swap register, the sounding interval changes, but knowing the inversion rules lets you track exactly what happens. It also speeds up recognition: if you already know a perfect fourth by ear, you halfway know a perfect fifth, because they are inversions of each other. Learn one interval well and its partner comes almost for the price of one.
Numbers add to nine, and quality flips (except perfect, which never changes). Master those two rules and every interval on the page instantly tells you about its inversion too.
The fastest way to lock this in is to hear it. Use the trainer below: identify an interval, then picture its inversion and predict what it should sound like before you check.
Interval ear trainer
Listen, then name the interval. Train the core skill behind playing by ear.
You will hear two notes. Identify the distance between them.
Go deeper
How to play piano by ear →Playing by ear is a trainable skill, not a gift. Here is how to build it, one interval and chord at a time.