Interval Size and Quality

Interval Size

In this article, we will cover what an interval is, and how they are measured in music. This is one of the most important articles in the course, so be sure to understand everything before moving on!

What is an interval?

An interval is simply a way of measuring the distance between two notes. For example, if we look on the piano, how many half steps are between the notes A and C? Well, A, A#, B, C-- that's 4 total. Intuitively, we might guess that this is how we name intervals. But, this isn't exactly it. Instead, in order to quickly be able to identify the interval, we name them based on the number of letters between the two notes. For example, A to C has a total of three letters (A, B, and C), so we call it a third. Similarly, if we have, for example, G to D, we would call it a fifth. What about a Eb to F?

That would be a second! We call this label the size of the interval. Why? well, because it is quite literally telling us the size, or how big the interval is. 

Now naturally, one question arises. How do we tell the difference between, say C to A, and C to A#? They would both be thirds, right? Well, yes they would. But we say that their quality is different.

The quality of an interval provides even more specific information compared to the size. There are five different types of qualities: perfect, major, minor, augmented, and diminished. Scales also have qualities; do you remember what differentiates a major and minor scale?

That's right, it's all about the third note. In a major scale, that note is a half step higher than in a minor scale. For example, the A major scale has a C#, whereas the A minor scale has a C. 

Thus, when we consider the quality of an interval, we can say that it follows the quality of the scale that it belongs in. For example, the interval A to C# would be a major third since C# appears in the A major scale, and the interval between A and C would be a minor third. What if the note appears in both scales, like the fourth or fifth interval? Well, then it would be considered perfect.

Before, I mentioned there were two other possible qualities: augmented and diminished. Well, these expand the interval ranges out by another half step. What do I mean? Well, if we have a minor third, and want to make it a diminished third, we need to lower the upper note by a half step. And if we have a major third that we want to make an augmented third, we need to raise it by a half step.

Let's take a look at this table to help clarify each of these.

As you can see, there are quite a few intervals to know!

The key to remembering them is simple: unisons, fourths, fifths, and octaves create perfect intervals, while seconds, thirds, sixths, and sevenths form major and minor intervals. Moving any interval up by an additional half step creates an augmented interval, and down by half step creates a diminished interval.

So, why do some of the interval names have multiple names separated by a slash? That's because two intervals can sound identical (i.e. have the same number of half steps), but actually encompass different pitch spellings. For example, D to G# and D to Ab are both 6 half steps, but would be named differently. What would we name them? Well, for the first one:
1. D-E-F-G is four note names, so the size is a fourth.
2. G is D major, so D# is a half-step above the perfect quality, making it an augmented interval.
3. Combining the two, we get an augmented fourth.

How would you name D to Ab?

The answer is a diminished fifth.

When two intervals like this sound the same but have different names, we call them enharmonic intervals.

Some intervals also have special names. For instance, the unison and octave are pretty self-explanatory, but the augmented fourth is also called a tritone. There's some pretty fascinating history with this interval that we won't get into (including associations with the devil!), but it is a pretty interesting Google search!

Let's pause briefly and practice. Answer the following questions:

Here are the answers:

Hearing intervals

Intervals can played in two different ways: harmonically and melodically. 

Harmonic intervals are two pitches played at the same time. Melodic intervals are played successively. Further categorizing melodic intervals, when a second is played (of any type), we call it a step. In other words, pitches of adjacent letter names being played melodically is called a step. All other intervals larger than a step are called a leap. When trying to write a catchy melody, having a good mix of steps and leaps is crucial!

By the end of the course, we should be familiar with the sound of the intervals I've introduced so far. Here are a few helpful videos that you may find useful when learning the sounds:

Here's the link to his entire Ear Training playlist: https://youtube.com/playlist?list=PLlx2eo2tD6Kr-Pjw7q8fVvLFXe4W1XmOw&si=WjF7vibzGufGyFFM

Here are the songs that I used while learning my intervals:

Minor second: Jaws Theme

Major second: Happy Birthday

Minor third: Mad World

Major third: Sir Duke

Perfect fourth: Bridal Chorus // Look Down

Tritone: The Simpsons

Perfect fifth: Star Wars

Minor sixth: The Entertainer

Major sixth: The Holly and the Ivy

Minor seventh: Tbh there's no real good song for this, so try to learn the sound on the piano!

Major seventh Pure Imagination

It should be noted that these songs should only be used as a reference tool to help develop your ear. Eventually (even if it is not within this class), you should be able to hear an interval being played and simply recognize it as the sound of that interval!

Consonance vs Dissonance

Consonance refers to intervals that are inherently stable, meaning they have no natural inclination to move (or resolve) to other sounds. When played harmonically, listen to how the perfect fourth, perfect fifth, and perfect octave sound consonant. These are called perfect consonances. Now, listen to some other consonant intervals like the minor 3rd, major 3rd, minor 6th, and major 6th. These are imperfect consonances.

Dissonance, then, refers to intervals that are inherently unstable, meaning they have a natural inclination to move to other, more consonant, sounds. For example, listen to how a tritone/diminished fifth and major seventh wants to resolve, and sound dissonant. Other dissonant intervals are the minor 2nd, major 2nd, minor 7th, and major 7th.

Practice

Practice ear training intervals here: https://www.teoria.com/en/exercises/ie.php

Practice identifying written intervals here: https://www.musictheory.net/exercises/interval

Look at these worksheets and try to solve them.

Citation 1:
Sanfilippo, Joshua M., "On the Pedagogy of Modes" (2025). Graduate Thesis and Dissertation post-2024.