Welcome to LivingPianos.com—I’m Robert Estrin. Have you ever wondered why certain intervals in music are called “perfect”? What makes them perfect, and why do they hold such a special place in music theory? The answers lie in the unique characteristics of perfect intervals and how they relate to other types of intervals. Let’s break it down in a simple and digestable way.
Two Categories of Intervals
First, it’s important to understand that there are two main categories of intervals in music: perfect intervals and major intervals. While there are more types of intervals, these two categories help you understand the foundation of music theory. Perfect intervals include the prime (unison), fourth, fifth, and octave. Major intervals include the second, third, sixth, and seventh.
What Makes Intervals “Perfect”?
The term “perfect” in perfect intervals comes from their unique ability to maintain their quality even when inverted. For example, the prime (also known as a unison) occurs when two notes are the same, like two middle Cs. It doesn’t matter if one of them is altered slightly with an accidental (a sharp or flat), the relationship between the two notes is still a prime.
Perfect intervals—prime, fourth, fifth, and octave—have a special property: when inverted, they remain perfect. For example, if you take a fifth and invert it, you get a fourth, and it’s still perfect. This is a fundamental difference between perfect intervals and other intervals, which I’ll explain shortly.
Major Intervals and Their Inversion
Now, let’s move on to major intervals. When you take a major third (for example, from C to E in C major) and invert it, you end up with a minor sixth (from E to C in this case). This is a crucial point: major intervals become minor when inverted, and vice versa.
What makes a major interval distinct is that it’s built on the notes of a major scale. So, in the C major scale, the second, third, sixth, and seventh notes of the scale are are all major intervals.
Inversion and the Change in Interval Quality
Inversion plays a big role in how intervals are perceived. As I mentioned earlier, when you invert a major interval, it turns into a minor interval. But what happens when you invert other types of intervals?
Augmented intervals (which are made by enlaring a perfect or major interval by a half step) become diminished intervals when inverted.
Diminished intervals (which are made by decreasing a perfect or minor interval by a half step) become augmented intervals when inverted.
It’s this inversion rule that sets the behavior of intervals apart and gives us a structured way to think about intervals in music.
Why Does This Matter?
Understanding these interval relationships can truly open up a deeper understanding of music. When you start to grasp how intervals change through inversion and how perfect intervals maintain their quality, it brings a sense of clarity and even enlightenment to your music.
A Quick Recap
Perfect intervals (prime, fourth, fifth, octave) remain perfect when inverted.
Major intervals (second, third, sixth, seventh) become minor when inverted.
Augmented intervals become diminished when inverted and vice versa.
It’s a lot to take in at first, but when you explore these concepts yourself, you’ll start to see how they impact the way music is structured.
Want to Learn More?
If you’re interested in learning more about music theory, technique, performance, and memorization, consider joining my Living Piano Mastermind Club. Click the link to get a free consultation. I look forward to helping you deepen your musical understanding!