Our focus in this lesson is on the relationship between fourth and fifth intervals.

Fourth and fifth intervals are related in so many ways. For example, the music clock:

…is either called the circle of fourths or the circle of fifths and this is because of the relationship between fourth and fifth intervals.

So, if you’ve always wanted to know what the relationship between fourth and fifth intervals is and why are they used interchangeably, this lesson is for you.

Let’s get started by refreshing our minds on fourth and fifth intervals.

## “*What Are Fourth Intervals?”*

Intervals are produced when two notes are played or heard together or separately.

It is a common practice to describe intervals using ordinal numbers like first, second, third, fourth, fifth, etc., and the ordinal number used is determined by the number of letter names (e.g. C, D, etc.) the interval encompasses.

A second interval encompasses two letter names. For example, the interval between C and D (C-D) is a second interval and this is because C-D encompasses two letter names (C and D):

*“Let’s Talk About Fourth Intervals…”*

Fourth intervals are unique because they encompass four letter names. So, any interval between two notes that are four letter names apart from each other is a fourth interval.

Between C and F:

…are four letter names: C, D, E, and F:

Therefore, C-F is a fourth interval.

The interval between F and B:

…is a fourth interval because there are four letter names encompassed: F, G, A, and B:

### Quick Insights On Fourth Interval Types

There are three known fourth interval types: the perfect fourth, the augmented fourth, and the diminished fourth interval.

Using C (as a reference):

…here are common fourth interval types:

C-F (perfect fourth):

C-F# (augmented fourth):

C-Fb (diminished fourth):

## A Short Note On Fifth Intervals

Fifth intervals encompass five letter names. For example, from C to G:

…is a fifth interval because five letter names are encompassed (C, D, E, F, and G):

The perfect fifth, the augmented fifth, and the diminished fifth interval are the commonly known fifth intervals.

*“Check Them Out…”*

Here are fifth interval types:

C-G (perfect fifth):

C-G# (augmented fifth):

C-Gb (diminished fifth):

## The Relationship Between Fourth And Fifth Intervals

Fourth and fifth intervals are related and the goal of this lesson is to show you the relationship between these two intervals.

Like I mentioned earlier in the introductory section of this post, the music clock is associated with fourth and fifth intervals; hence, it’s either called the circle of fourths or the circle of fifths.

Now the question is this:

“What is the relationship between fourth and fifth intervals?”

I’ll be showing you what fourth and fifth intervals have in common in this lesson.

*“What Is The Relationship Between Fourth And Fifth Intervals?”*

The inversion of an interval is simply the change of the order of the notes it’s made up of.

For example, the inversion of the interval “C-D”:

…is simply changing the order of the notes from “C-D” to “D-C”:

C-D:

D-C:

Both intervals (C-D and D-C) are still made up of the same notes (C and D), but the order of the notes is the difference between C-D and D-C.

*“Don’t Miss This Point…”*

Fourth and fifth intervals are related by the concept of inversion. The inversion of fourth intervals produces fifth intervals and vice-versa.

Let’s take a critical look at the inversion of fourth and fifth intervals.

### The Inversion Of Fourth Intervals

The interval between C and F (which is C-F) is a fourth interval; encompassing C, D, E, and F (four letter names):

The inversion of C-F:

…produces F-C:

…which is a fifth interval. F-C is a fifth interval because it encompasses five letter names: F, G, A, B, and C:

So, the inversion of a fourth interval produces a fifth interval and this is true for ALL fourth intervals.

### The Inversion Of Fifth Intervals

The inversion of fifth intervals produce fourth intervals. For example, the fifth interval between C and G (produces C-G):

…which is a fifth interval because C, D, E, F, and G:

…are encompassed.

The inversion of C-G (a fifth interval):

…produces G-C (a fourth interval):

…encompassing four letter names (G, A, B, and C):

You can clearly see the relationship between fifth and fourth intervals as it relates to the inversion of chords. All fifth intervals are changed to fourth intervals when inverted.

## Final Words

Understanding the relationship between fourth and fifth intervals will help you associate ALL fourth intervals with fifth intervals.

When you come across people who are arguing about the music clock, you can say:

Circle of fourths = Circle of fifths

…and also tell them why.

We’re not done with intervals yet; we’re only getting started. However, if you have questions, comments, contributions, and suggestions, feel free to post them in the comment section and don”t forget to follow us on Facebook and Youtube.

See you in the next lesson.

#### Chuku Onyemachi

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{ 1 comment… read it below or add one }

Thanks, very much. I have always wanted to understand Intervals and you explained it so simple. I appreciate this Information very much. Thank you for your effort and time, putting this together in the simple form imagined. God bless you.