Tonal Families: Introduction to Chord Substitution - Function 1
Updated: Jan 19
Example C Major scale in piano chords
Within a scale, we have seven diatonic chords. With the term diatonic I mean chords that belong to a specific scale. By looking at the triads we build on top of every note (or degree when referring to a harmonic function) it is possible to group the chords into families – or harmonic functions, if you prefer – that share similar harmonic properties. As each note has a specific function within a scale, the chord above it does as well. This will be particularly useful when we implement chord substitutions, which is very useful in writing or arranging songs and in Jazz improvisation as well.
But what is a harmonic function in the first place?
We can define it as the role that a particular chord plays in the creating of a larger harmonic progression, either belonging to the scale (diatonic chords) or not belonging to it (chromatic chords). In this article we will focus on the diatonic triads.
Let’s see an example in C major scale in the image above, and let's take it to explain the chord substitution.
Within the diatonic chords, we can classify the harmonic functions into 3 main ones:
1 - Tonic family
2 - Subdominant family (also called Pre-Dominant)
3 - Dominant family
1 – Tonic Family
These three families have a specific purpose and effect within a harmonic progression. Let’s delve into this topic: In general terms, in music, we can talk about three different moments: stability, local activity and directional motion.
The tonal family chords portray the stability within a harmonic progression. This means that we can stay longer on these chords without the risk of a monotonous effect. They set the key in which the music is and the rest of the chords will have a natural tendency to go back to tonal family chords; they tend to express the tonal foundation of the piece as well and therefore, they are often seen at the beginning and end of a piece or section.
Within a scale, they are represented by the Tonic or First degree (I), the Mediant or third-degree (III) and the Sub-Mediant or sixth degree (VI)
The intervallic relations between these three chords is simple: from the tonic, we move 3 notes down to the VI and if we move three notes up from the same note we will arrive at the III. Here we have an example in the key of C major:
Now see how this is translated to musical notation:
See above how the three chords are intertwined: they always share two notes between the tonic chord and the rest of the chords of the same family.
In the next articles, we will see the Subdominant (function 2) and Dominant family (function 3) and how they interact ( i iv v chords).