Music notes creating the interval of an octave

Intervals in Music: An Introduction

If a deeper understanding of music theory is important to you, you absolutely must understand intervals. Intervals are a foundational piece of the puzzle to several more complicated musical concepts including scales, chords, ear-training, counterpoint, and more.

Here I’ll explain everything you need to know about intervals to help you on your way to music mastery!

What Is An Interval?

Music notation
Photo by hermaion from Pexels

In the English language the word “interval” is used for several other things, but they all have to do with distance of either time or space. Interval training, for example, is referring to the interval of time you spend, say, 1 minute, between switching exercises. If you were building a fence you might say you’d like the fence posts to be placed at 10 foot intervals, meaning you’d like 10 feet between each fence post.

Similarly, in music we use the word interval to talk about the distance in pitch between two notes.

Where Do We Find Intervals?

Musical intervals are everywhere. Any time there’s more than one note being sounded, there’s an interval. Even if it’s the same note played twice, there’s still a name for that interval! If you’ve ever noticed that train horns sound more than one note simultaneously, then you know there’s an interval there too!

This is all because an interval isn’t exactly something itself, but rather a way to describe the relationship of the two notes it’s comprised of.

Melodic and Harmonic Intervals

It’s important to understand that any two notes are always creating an interval. If they’re played one at a time, like in a melody, we call it a Melodic Interval. If they’re played simultaneously, or in harmony with each other like the above train horn example, we call it a Harmonic Interval. That’s simple enough, right?

How to Talk About Musical Intervals

The word definition in a dictionary
Image by PDPics from Pixabay

There are two parts to defining a musical interval. First there’s a descriptor, which is followed by a number. Let’s talk about the numbers first.

The most commonly used intervals in music are within one octave (which is the interval of an 8th). There’s really no limit to how big an interval can be (besides perhaps the capabilities of the instrument you’re using to play the notes), but for our purposes we will only discuss those within an octave*.

(*Several intervals outside of the octave are frequently used in music, but that’s beyond the scope of this article. Once you understand how intervals work within the octave, it will be easy to understand those outside of it.)

Here’s a list of all the numeric intervals within an octave and one way to play them on a piano using the C major scale*:

Piano keyboard with two Cs on the same C key: The interval of a unison
1st, also called a unison: C to the same C
Piano keyboard with a C on the C key and a D on the D key: The interval of a second
2nd: C to D
Piano keyboard with a C on the C key and an E on the E key: The interval of a 3rd
3rd: C to E
Piano keyboard with a C on the C key and an F on the F key: The interval of a 4th
4th: C to F
Piano keyboard with a C on the C key and a G on the G key: The interval of a 5th
5th: C to G
Piano keyboard with a C on the C key and an A on the A key: The interval of a 6th
6th: C to A
Piano keyboard with a C on the C key and a B on the B key: The interval of a 7th
7th: C to B
Piano keyboard with a C on the C key and another C on the next higher C key: The interval of an octave
8th or octave: C to the next C up or down the keyboard

*Notice that if you count the white keys, including the starting and ending keys, as you play the notes in the above examples the number you’ll count to will be the same as the numeric name of the interval.

How to Recognize Intervals in Musical Notation

Similarly, when the same intervals are notated you’ll see that you have the same results when counting the notes between intervals, including the starting and ending notes.

Being able to recognize intervals at a glance is extremely useful for sight-reading purposes. It makes it so that you only have to read one note, and for the rest can instead just see the relationship from the first note to the next. This saves a lot of time and mental work, especially when there are a lot of notes on the page!

Perhaps when you started learning music your teacher taught you about “steps” and “skips”. These are just a simplified way of talking about the interval of a 2nd (steps) and the interval of a 3rd (skips).

Just like how you may have learned that a step (or 2nd) always goes from a line note to a space note, or a space no to a line note, and a skip (or 3rd) always goes from a line note to another line note, or a space note to another space note, all the other intervals have a similar pattern.

As a rule, the odd-numbered intervals go from line to line or space to space and the even-numbered intervals go from line to space or space to line.

Notated intervals in the key of C
Melodic and Harmonic Intervals in C Major

Digging Deeper Into Intervals

Old-looking sheet music
Image by cocoparisienne from Pixabay

So far, the types of intervals we’ve been looking at can be described as diatonic. This means that all the notes can be found within the key (in our case, the key of C Major).

If there had been any sharp or flat notes in the example I gave you, those would not be diatonic as there are no sharp or flat notes in the key of C major. Instead, we would call those chromatic intervals. I will talk more about chromatic intervals in a future post.

We’re almost ready to discuss that descriptor I mentioned above, but first I want to differentiate our intervals in one more important way.

Perfect vs. Imperfect Intervals

A sign that says to me, you are perfect

This differentiation has to do with the ratios created by the frequencies of the two notes at any given interval. This sounds super complicated, and for our purposes it’s not necessary to understand the fine details of this.

Basically the ratios created by perfect intervals are pure, whole numbers. The perfect intervals are unisons, 4ths, 5ths, and octaves.

Imperfect intervals create ratios that are more complicated. As you may have already figured out via the process of elimination, the imperfect intervals are 2nds, 3rds, 6ths, and 7ths.

Fun fact: If you compare how the notes sound together in perfect intervals vs. imperfect intervals, you’ll notice that the “beats” of the sound tend to be faster with imperfect intervals. This is the sound of those two frequencies interacting in a more chaotic way, creating that complicated ratio.

Different Types of Imperfect Intervals

There are four different ways to describe an imperfect interval. From smallest to biggest they are diminished, minor, major, and augmented. (As a side note, the same four words are used to describe the four types of triads. If you’re interested, I’ll soon be publishing an article on Chords: An Introduction to Triads. Stay tuned!)

For the purposes of this article, we are only going to discuss the major and minor intervals, as they’re much more common than the others.

Diatonic Intervals in a Major Key

There are a few different ways to go about figuring out which one is which. One way is to consider it from the perspective of the scale or tonal center. If you look back at the interval examples above, you’ll recall I said those are the intervals within the C major scale. Any diatonic, imperfect interval in a major key will be a major interval.

So the diatonic 3rd could also be called a major 3rd, or M3 for short. Similarly, we had a major 2nd (M2), a major 6th (M6), and a major 7th (M7) in that example.*

(*Note: The perfect intervals are all just called perfect; P1, P4, P5, and P8)

Notated harmonic intervals in C major
Diatonic Harmonic Intervals in the Key of C Major

Diatonic Intervals in a Minor Key

Now what if we switched to the key of C minor, and wanted to change the notes in the example as necessary to keep the intervals diatonic? That means we need to alter some of the notes in the example to match the new key of C minor, which has three flats. After these changes the E would now be E flat, the A would be A flat, and the B would be B flat.

Unfortunately, intervals in the minor scale are not quite as clean and tidy as in the major scale. Almost all of the imperfect intervals are now minor, except one. Can you guess which one?

Of course, it’s the 2nd, because we didn’t change the C or the D, so the 2nd still must be a major second.

The other three imperfect intervals though, are now minor. We have a minor 3rd (or m3) from C to E flat, a minor 6th (m6) from C to a flat, and a minor 7th (m7) from C to B flat.*

(*Note: The perfect intervals are still just perfect, even in a minor scale. Why mess with perfection?!)

Musical notation of harmonic intervals in C minor
Diatonic Harmonic Intervals in the Key of C Minor

Comparing Major and Minor Intervals

Take a look at the Minor and Major 2nds in the example below. Which one is bigger? C to D is bigger because D is a higher pitch than D flat, so there’s more space between C and D. This is the same with all major and minor intervals. The major interval is always a half step (or minor 2nd!) bigger than a minor interval.

Musical notation of Major and minor intervals in C
Major and Minor Melodic Intervals Starting on C

In Summary

I went into a lot of detail here to explain exactly what intervals are and how they work, but I hope you’ve come away with a firmer grasp of this very important concept. Here’s a quick summary of the most important points:

  • An interval describes the distance between two notes.
  • The number of an interval can be found by counting the notes either of a scale or on the staff.
  • Unisons, 4ths, 5ths, and octaves are perfect intervals.
  • 2nds, 3rd, 6ths, and 7ths are imperfect intervals.
  • In a major scale, the imperfect intervals are all major.
  • In a minor scale, the 3rd, 6ths, and 7ths change to minor.
  • Perfect intervals remain perfect whether in a major or minor scale.

I want to point out that I’ve only discussed one way of looking at intervals in this article. I did this for the sake of simplicity, but in future articles I’ll be sure to discuss the other ways so you can understand them more fully, because there’s a lot more to know!

Make Practice Time Easier By Planning Ahead!

Hands playing piano keys with a metronome and pencil nearby

Learn how to plan exactly what you need to do each day to accomplish your goals. Then all you have to do at practice time is sit down and play!

The Piecewise Practice Planner will help you make meaningful progress every time you practice, even with as little as 5 minutes per practice session.

Best of all, it’s completely FREE–to opt in, click the button below!

Did you find this article helpful? Or did you just end up more confused? I’d love to hear from you in the comments below!

Heidi has been involved in music in one way or another for most of her life. She studied music composition in college, has taught piano, voice, composition, ear training, and guitar, and has worked as a piano tuner and technician. Before the pandemic she loved playing concerts at retirement communities, bringing the joy of music to those populations. She is currently working on learning more about the connection between music and healing.

Related Articles:

Music Theory: If You Don’t Think It’s Important, You’re Wrong
The Role of Melody in Music
How to Read Music Notes

Leave a Comment

Your email address will not be published. Required fields are marked *