How to Write Harmonic Progressions Using Chord Substitution

Our last music theory lesson discussed harmonic sequences, including the circle-of-fifths progression. However, sequences are not the only way to achieve convincing harmonic progressions.

Do you remember the primary triads, I, IV and V? We’ve already said that they are the basic harmonic framework for most tonal music. But most music lovers would agree that music would get rather boring if only these three chords were used all of the time.

Introducing the Secondary Triads

Secondary triads are the rest of the triads of a diatonic scale (ii, iii, vi, vii°). These triads often are used as substitutes for the primary triads (I, IV, V), to add richness and variety to the music.

A triad a third below each of the primary triads is said to be its secondary counterpart. Let’s start with the tonic chord.

Tonic Class Chords

Notice that the tonic and submediant triads have two common tones, which makes them very closely related in sound. This makes it very easy to substitute the I chord with a vi chord in a chord progression. Because the vi chord can easily be used in place of the tonic (I) chord, we classify both chords (I and vi) as tonic class chords. As you’ll see later, we’ll use these classifications to help us build good harmonic progressions. Compare these two progressions:

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The first progression is the basic primary triad progression (I-IV-V-I). The second progression substitutes the final I chord with a vi chord. Do you hear how it adds freshness to the sound? Additionally, it gives the music a sense of forward motion because it sounds incomplete because the expected V-I is denied. We call the last two chords (V-vi) of this progression, a deceptive cadence. Also there is something unusual about the voice leading from the V-vi. Can you tell what it is? And why is the voice leading different from a normal progression by second?

Now let’s look at the substitute for the IV chord:

Subdominant Class Chords

Again, notice that the IV chord and the ii chord have two common tones. And using the same basic primary-triad progression (I-IV-V-I), we’ll substitute the IV chord with the ii chord:

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First, you should notice that both progressions sound very much alike. You might also notice some unusual voice leading in the progression with the ii chord. There are many aspects that come into play when using chord substitutions, for example using seventh chords and chord inversions to make the substitutions sound smoother and richer. We’ll get to those later; but the purpose of this lesson is simply to present you with the concept of chord substitution.

Dominant Class Chords

The most common substitution for the dominant chord is the vii° chord. The iii chord also may substitute for the dominant chord, but only under certain circumstances.. The dominant chord (V) is such a strong chord, that using a substitution gets a bit tricky. Therefore, we’ll save this substitution for later when we talk more about chord inversions.

Let’s review the chord classes: