Where to start? You may have wondered about the meaning of these blue chords with the roman number in front of the chord name that you can see in the MelodyBuilder chord database when selecting a minor or major scale. These chords are in some way special – of course.

Let’s make it simple and skip the scientific explanation. A major or minor scale consists of 7 notes. For each of these notes exists exactly one 3 note chord that is only using the 7 scale notes as base material and that is either a minor, major, augmented or diminished chord (in MelodyBuilder they get the suffix min, maj, aug or dim, e.g. Amin, Amaj, Aaug, Adim).

You can extend this system into 4 or 5 chord notes by adding suffixes to the numeral like a V7 chord that indicate what notes you added to the base chord, but it doesn’t really matter for understanding the principle.

The seven scale steps / diatonic functions

So here is the trick. Each of the 7 scale notes is assumed to have a certain function within the set of scale notes. Also the 7 chords built on these notes are assumed to have a certain function.

Let’s take the A minor scale as an example, that consists of all the white keys on a piano keyboard: A, B, C, D, E, F, G. The seven steps are as follows:

Index Name Chord
I Tonic Am (A, C, E)
II Supertonic / Subdominant parallel Bdim (B, D, F)
III Mediant / Dominant parallel Cmaj (C, E, G)
IV Subdominant Dm (D, F, A)
V Dominant Em (E, G, B)
VI Submediant / Tonic parallel Fmaj (F, A, C)
VII Subtonic / Leading Gmaj (G, B, D)

Now what is the function of each step?

The main functions

There are three main functions: the tonic(I), the dominant(V) and the subdominant(IV). They are somehow the pillars of a chord progression (if you follow the traditional way).

I Tonic

The tonic is the tonal centre. If you think of a chord progression as a movement or journey that starts somewhere on any other step in the scale chords, there is some kind of “need” to at some point reach the tonic and resolve all the tension that was created during the journey in the tonic.

This chord is either a minor chord in a minor scale or a major chord in a major scale. It also gives the scale its name, e.g. the first chord in the A minor scale is the A minor chord.

IV Subdominant

The subdominant is a counter-part to the dominant chord (V). Although the subdominant wants to return to the tonic, it is often perceived as a resting point in the journey of your chord progression.

V Dominant

The purpose of the fifth chord, the dominant, could be described as: creating instability. It turns the journey of your chord progression in a direction where at some point you expect to get the instability resolved by the tonic. This is partly due to the lowest note in the dominant (the bass note) being the highest note of the tonic.

The secondary functions

The other functions, well, let’s say they are there to keep the journey interesting. For example, Let it be from the Beatles starts with a progression I – V – IV. To make it more interesting, somebody put two more chords in to end up with I – V – VII – II – IV. Leave the II out and you have the first half of Alphaville’s Forever Young.

This chord group consists of the so-called parallels (supertonic/ subdominant parallel, mediant / dominant parallel, submediant / tonic parallel) and the subtonic. The parallels are called this way because they share two notes with their main chord and hence sound similar to the main chord. They can be used in a similar way but they add more friction/tension.

And what does this have to do with cadences?

Well, a cadence is a chord progression that only uses these 7 scale chords (plus their 4 notes chords, 5 notes chords extensions) and feels in some way complete or provides a resolution. That does not mean that every cadence has to end in the ultimate resolution, the tonic. It’s just about the feel of completeness. Your whole chord progression can be a cadence or only the last two chords of it.

There are 4 basic types of cadences:

1. Authentic cadence

This cadence sounds “complete”. It moves from the dominant(V) to the tonic(I). The dominant creates some instability that wants to be resolved and the tonic is the ultimate resolution. Usually instead of the V chord you use the V7 chord, e.g. in the A minor scale, instead of the chord Em (notes: E, G, B) you use the chord Em7 (notes: E, G, B, D).

This cadence comes in two different forms:

  • Perfect authentic cadence: The chords are unaltered in their note order.
  • Imperfect authentic cadence: The chords are altered, e.g. inverted by putting the highest note into the bass or by substituting the V chord.

2. Plagal cadence

The cadence IV – I (subdominant to tonic) is called the plagal cadence, also called the amen cadence because it was often used in blues, gospel and religious music.

3. Half cadence

Any cadence is called a half cadence if it ends on V (the dominant).

4. Deceptive cadence

The cadence V – VI, for example I – IV – V7 – VI. It’s called deceptive because it creates an expectation where the progression will go and then ends up in a very different place.