This lesson is for anyone who is yet to discover the power of third intervals in music.

There’s no better way to start this lesson than taking a look at third intervals. But before we do that, let’s take a look at the definition of the interval.

## A Short Note On Intervals

An interval is the relationship between **two** notes (whether played together or separately) in terms of the distance between them.

I want to emphasize the part of the definition that says “*relationship between two notes”* because it says a lot about the nature of intervals. Before we talk about “the relationship”, it is important that you note that it takes only two notes.

It takes (the relationship between) two notes to form an interval. These are examples of intervals…

C and Eb:

A and F#:

E and B:

…and the list goes on and on.

It practically takes any two notes to form an interval. However, the identity of the interval is tied to a scale relationship. If you don’t believe it, here’s the scale relationship between the notes of the intervals listed earlier:

C and Eb:

…the first and third tones of the C minor scale:

A and F#:

…the first and sixth tones of the A major scale:

E and B:

…the first and fifth tones of the E major scale:

That’s what you should know about intervals in this lesson. If you want to know more about intervals, follow the suggested reading below:

Suggested Reading: Beyond Distance: The Second Dimension Of Intervals and Exposed: Six Characteristic Features Of Intervals.

*“What Are Third Intervals?”*

The number of scale tones encompassed by an interval is described using ordinal numbers like first, second, third, fourth…ninth, tenth, etc. Third intervals are intervals that encompass three scale tones.

*“Check out these third intervals…”*

C and E:

…encompassing the first three letter names of the C major scale:

…from C to E:

D and F:

…encompassing the first three letter names of the D minor scale:

…from D to F:

G and B:

…encompassing the first three letter names of the G major scale:

…from G to B:

### Qualities Of Third Intervals

The term *third *does not state the exact size of an interval. For example, C-E:

…and D-F:

…are all third intervals, however, they have different sizes. C and E:

…contains four half steps while D and F:

…contains three half steps.

Due to the fact that the use of the term “third” does not state the exact number of half steps a third interval contains, certain adjectives are used to describe and qualify various sizes of third intervals.

*“Check Out These Sizes Of Third Intervals…”*

**#1 – The Diminished Third**

The third interval with the smallest number of half steps is the diminished third interval and it contains two half steps. These intervals below…

D# and F:

E and Gb:

A# and C:

B and Db:

…are diminished third intervals and encompass the distance of two half steps each.

**#2 – The Minor Third**

The minor third interval is a product of the relationship between the first and third tones of the minor scale and encompasses a distance of three half steps. Here are some of them below…

D and F:

E and G:

A and C:

B and D:

**#3 – The Major Third**

The relationship between the first and third tones of the major scale produces the major third interval. The major third interval encompasses a distance of three half steps. Check them out…

D and F#:

E and G#:

A and C#:

B and D#:

**#4 – The Augmented Third**

The augmented third interval has the biggest width – encompassing five half steps. Below are a few examples…

Db and F#:

Eb and G#:

Ab and C#:

Bb and D#:

…are diminished third intervals and encompass the distance of two half steps each.

*“In a nutshell…”*

All third intervals are not equal. The intervals below…

- D# and F
- D and F
- D and F#
- Db and F#

…are all third intervals, however, playing them on the piano shows their difference in size.

D# and F:

…is a diminished third interval.

D and F:

…is a minor third interval.

D and F#:

…is a major third interval.

Db and F#:

…is an augmented third interval.

## The Major And Minor Third Intervals

Although there are four known qualities of the interval, we’ll be focusing on the major and minor third intervals.

**Attention:** According to music scholars, the augmented and diminished intervals sound unpleasant, consequently, they are rarely used in harmony or chord formation. Check out this lesson on dissonant intervals to learn more.

### The Major Third Interval

The relationship between the first and third tones of any given major scale produces the major third interval. Using the C major scale:

…the major third interval can be formed by a relationship between its first and third tones:

…which are C and E respectively.

Here are the major third interval in all twelve keys:

C major third interval:

Db major third interval:

D major third interval:

Eb major third interval:

E major third interval:

F major third interval:

F# major third interval:

G major third interval:

Ab major third interval:

A major third interval:

Bb major third interval:

B major third interval:

### The Minor Third Interval

The minor third interval is formed by the relationship between the first and third tones of any given minor scale. The first and third tones of the C natural minor scale:

…which are C and Eb:

…produces a C minor third interval.

**Attention:** Minor third intervals are smaller than major third intervals by a half step.

Here are the minor third interval in all twelve keys:

C minor third interval:

C# minor third interval:

D minor third interval:

Eb minor third interval:

E minor third interval:

F minor third interval:

F# minor third interval:

G minor third interval:

G# minor third interval:

A minor third interval:

Bb minor third interval:

B minor third interval:

**The Harmonic Potential Of Third Intervals**

In the formation of chords, the relationship between notes is based on what music scholars call classes of harmony. There are three classes of harmony – secundal, tertian, and quartal harmony.

*“Let me explain these classes of harmony briefly…” *

**Secundal harmony** is the product of playing notes that are a second apart from each other.

**Tertian harmony** is the outcome of playing notes that are a third apart from each other.

**Quartal harmony** is the outcome of playing notes that are a fourth apart from each other.

Using the C major scale:

…as an underlying scale, here are secundal:

…tertian:

…and quartal:

…chords.

Although any class of harmony can be used in chord formation, thirds are commonly used in traditional practice and this makes the **tertian harmony** the traditional class of harmony.

### The Tertian Harmony

A collection of notes played in third intervals are in tertian harmony.

Third intervals are of the greatest possible importance in chord formation due to the fact that the tertian harmony is the principal class of harmony.

This means that chords are formed by the relationship between notes that are apart from each other in interval of thirds.

*“Check this out…”*

The C major triad is formed by stacking the notes of the C major scale:

…in thirds.

A third from C:

…is E:

…and another third from C-E:

…is G:

Altogether, the C major triad:

…which can be broken down into two third intervals…

C-E:

…a C major third interval and E-G:

…an E minor third interval.

### The Intervallic Breakdown Of Chords

Chords can be called harmonic structures because they are built by stacking notes, consequently, chords can be broken down into intervals and this is known as the intervallic breakdown of chords.

All tertian chords (irrespective of how big or small they are) can be broken down into third intervals.

The C minor 11th chord:

…can be broken down into 5 third intervals:

C minor third interval:

Eb major third interval:

G minor third interval:

Bb major third interval:

D minor third interval:

### The Power Of Third Intervals

In a nutshell, third intervals are important in harmony because they are potential triads, seventh, and extended chords. Stacking major and minor thirds produce chords of various classes.

*“Check out these examples…”*

The C major third interval:

…and the E minor third interval:

…produces the **C major triad**:

…if stacked together.

The C major third interval:

…and the E major third interval:

…produces the **C augmented triad**:

…if stacked together.

The C minor third interval:

…and the Eb major third interval:

…produces the **C minor triad**:

…if stacked together.

The C minor third interval:

…and the Eb minor third interval:

…produces the **C diminished triad**:

…if stacked together.

## Final Thoughts On Thirds

The knowledge of third intervals is useful in harmony. When a given note is to be harmonized, there are four options of notes that can harmonize the given note.

*“Check it out…”*

To harmonize C:

…here are four options of the notes to consider…

- Eb
- E
- A
- Ab

…and I guess you want to know why.

Harmonization of C:

…with Eb:

…produces C-Eb:

…a minor **third** interval.

Harmonization of C:

…with E:

…produces C-E:

…a major **third** interval.

Harmonization of C:

…with A:

…produces A-C:

…a minor **third** interval.

Harmonization of C:

…with Ab:

…produces Ab-C:

…a major **third** interval.

All four options have one thing in common – a third. In another lesson on *“How To Harmonize A Note”*, we’ll explore these options.

See you then!

{ 2 comments… read them below or add one }

Excellence and easy to follow. This has answered many of the music theories that have always bothered me. Thanks a lot.

From this lesson I am able to see for example how the accidents in the music structure come about. To day i can differentiate a minor scale from a Major scale.