Introduction

In this lesson, we're going to stack minor and major thirds in three different ways, and examine the chords and key signatures which result.

1. Stacking minor thirds.

2. Stacking major thirds.

3. Alternate Stacking, minor and major.

Stacking major thirds.

A major third is two tones in distance, let's examine what happens when we stack major thirds on the piano starting on middle C. This is called a whole tone scale and there are only four possible starting locations before we have a repeating pattern. The whole tone scale has only three notes, so there are three modes, however, there is only one unique mode. Also observe the whole tone scale is also a augmented chord and it doesn't matter which note you consider the root, it will always be an augmented chords. Also observe how this makes perfect sense because an octave is divided into twelve semi-tones, and twelve divided by four is three, three notes in the scale.  

Harmonic Formula: 1 3 +5 

Stacking minor thirds.

A minor third is one and a half semi-tones in distance, let's examine what happens when we stack minor thirds on the piano starting on middle C. A minor third scale is a four note scale constructed with stacked minor thirds. There are only three possible starting location before the pattern repeats. Because the minor third scale has four notes, there must be four modes, however there is only one unique mode to this scale. This scale is also called a fully diminished chords as the melodic interval series for this scale is root, semi-tone, semi-tone, semi-tone, semi-tone. Also observe an octave divided in four is one and a half semi-tones.

Harmonic Formula: 1 -3 -5

Stacking alternating major and minor thirds.

Let's examine what happens when we alternatively stack major and minor thirds on the piano keyboard starting on the note C. We've constructed the circle of thirds first encountered in Lesson 18.  The circle of thirds lies within the circle of fifths because a fifth is the stacking of a minor and major third OR a major and minor third.

Depending on the starting note, you will get two patterns;

Harmonic Formula: 1 3 5 7 

Harmonic Formula: 1 -3 5 -7

These four note patterns may be represented as the chords XM7 and Xm7.