Chords within a key can be numbered to more easily understand the functional harmony of a song and to also aid in memorising chord progressions.

In the early stages of playing we often we see songs as just long streams of unrelated chords but it’s important to know that the same chord patterns appear time and time again. Learning these patterns by number can help recognise sequences in any key and also give you a better understanding of they all relate to each other.

This Lesson is a preview of the Bassic Fundamentals Course 

Numbering The Major Scale

We can assign a number to each degree of the major scale by starting from the root and working up.

D  E  F  G  A  B  C
  2  3  4   5   6   7  8 

We can then build a chord off of each degree and add the chordal quality.

Chord I – Major
Chord II – Minor
Chord III – Minor
Chord IV – Major
Chord V – Major
Chord VI – Minor
Chord VII – Diminished

In the key of C major the chords would look like this:

Chord I – C Major
Chord II – D Minor
Chord III – E Minor
Chord IV – F Major
Chord V – G Major
Chord VI – A Minor
Chord VII – B Diminished

Memorising this is easier if you remember that chords I, IV and V are major. All the rest are minor except for VII which is diminished. 

This sequence of chords is exactly the same in every key. Here’s G major for example:

Chord I – G Major
Chord II – A Minor
Chord III – B Minor
Chord IV – C Major
Chord V – D Major
Chord VI – E Minor
Chord VII – F# Diminished

Chord Progressions By Number

Now we’ve numbered every chord in a key, we can begin to refer to chord sequences in the same way. Take this progression for example:

C Major | A minor | D minor | G Major

We know that we are in the key of C Major, so the first chord must be chord I. Then we can simply count up the scale to find out what the other chords are.

| Am | Dm | G
I   |  vi     ii   | V

Now we know the sequence, we can transpose the chords into any other key. Here is the sequence in G:

| Em | Am | D
I   |  vi     ii   | V

Every chord in a key has its own sound and transposing chord sequences will help you hear how each chord relates to its scale.

Roman Numerals 

Chord numbers are often represented by their roman counterparts.

1 – I
2 – ii
3 – iii
4 – IV
5 – V
6 – vi
7 – vii

Capitalised numbers represent major chords.

Lowercase numbers represent minor chords.

Recognising Common Chord Sequences

Chords I, IV and V are what we call primary chords. They are used in thousands of songs so it is really important to know what they sound like so you can recognise them by ear.

As an exercise, create your own short sequence using chords I, IV and V in C. Play through this sequence a few times and then try transposing it to a new key. You will hear how the sequence sounds the same despite using different notes. To take this exercise further, use other chords in the key such as ii and vi so you can hear how they are used alongside the others.

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