A creative pianist is well-served by learning not just chords, but the relationship between chords. Why some chords are better choices for a harmonic progression is useful knowledge, particularly for budding composers and arrangers, though it can also be useful for improvising and understanding the finer points of interpreting a jazz standard. In this post, we’ll get started by exploring why a given chord sounds more (or less) “stable.”

Scale Degrees – From Stable to Unstable

Tonal music is music organized around a center, also known as the “tonic.” The first note of a major scale, for example, C in a C major scale, is the tonic. Every note in a scale, and the chords constructed from those notes, has a relationship to the tonic.

Chords are built from scales, so to better understand chords and their relationship to each other, it makes sense to understand how each tone of a scale functions. Let’s use the C major scale to investigate this.

Each tone or degree of a major scale has a certain degree of stability. The 1st, 3rd and 5th degrees of the scale sound relatively stable to us. They give us the feeling that we could “stay put” on these tones:

Example 1


The other tones in the major scale are less stable. If you listen closely, you’ll notice that the 4th degree (F)  sounds like it wants to resolve its instability by moving to 3 (E) or 5 (G):

Example 2



The 7th degree (B) wants to resolve to the 1st degree (C):

Example 3



The 2nd wants to resolve to the 1st or 3rd degree:

Example 4



And the 6th wants to resolve to the 5th degree:

Example 5



To summarize:  the 1st, 3rd and 5th degrees of the scale are relatively stable. The 2nd and 6th degrees are somewhat unstable. The 4th and 7th degrees are very unstable. As you’ll soon see, the stability of each scale tone is the reason that certain chords feel stable or grounded to us, while others feel unstable and in need of resolution. Understanding this is the basis of creating effective chord progressions, or analyzing a composed progression in order to improve your interpretation of it.

From Scale Tones to Chords

Chords can be built by stacking intervals of a 3rd on each tone of the C major scale. Together, these chords comprise the diatonic chord progression. Each chord is traditionally labeled with a Roman numeral. In both classical and jazz/pop harmony, three of these chords are the most commonly-used: the tonic (I) chord, the subdominant (IV) chord, and the dominant (V) chord:

Example 6

The tonic (I) chord is the most stable chord in the diatonic progression. Why? Because it’s constructed from scale degrees 1, 3 and 5 – which are all stable tones!

The subdominant (IV) chord is less stable than the tonic chord. This is because the bottom note of the chord (F) is the 4th degree of the major scale, which you’ll recall is quite unstable. However, the top note of the chord (C) is the 1st degree of the scale, which keeps the chord from being too unstable.

The dominant chord is the most unstable chord of the three. While it contains one fairly stable scale degree (the 5th), it also contains the 7th and 2nd degrees of the major scale, which are both unstable. If the dominant chord is a tetrad (a four-note chord, consisting of G-B-D-F), the interval established by the 7th degree of the scale (B) and 4th (F) (known as a “tritone”) particularly begs for resolution. This instability is why the dominant 7 chord is used in most cadences (brief harmonic progressions that suggest a conclusion).

In a future post, I’ll build on this understanding of chord stability to explain why certain chords work better than others at a given position in a chord progression.

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