Theory lesson: chords of the major scale – diatonic chords

When you have a chord progression and want to use a scale to improvise over the top how do you know which scale to use? When you’re listening to your favourite song and trying to figure out the chords which ones do you try? If you know which chords are in each key then it will make both of these tasks easier.

Each musical key has a group of chords that go together. These chords are built from the notes of the scale attached to that key. These are known as diatonic chords.

In this lesson we will have a look at how to figure out the chords for any major key. If you haven’t already have a look a the lesson on major scales for guitar, bass, banjo, mandolin or ukulele. This information will come in useful when doing this lesson.

We will use the key of C major for this lesson. it is the easiest key to use as there are no sharps or flats in the C major scale. Here are the notes of the C major scale in order.

C major scale numbered

Each note in the scale has a chord that is associated with it. The notes for all the chords are taken from the key. Once you know the pattern to follow you can figure out what each chord is.

We already know that a C major chord is made up of the 1st, 3rd and 5th notes of the C major scale. This is the C major triad as there is only one of each note (usually when we play a chord it is bulked out with duplicates of some notes).

C major triad numbered

When we create this chord we skip the 2nd and 4th notes. If we use that pattern of skipping notes we can figure out the other chords used in the key of C major.

Lets start on a D note and skip the 3rd and 5th notes to create the triad based on the D note in the key of C.

D minor triad numbered

We can follow this pattern to create all the triads in the key of C. Once we get to the B note at the end of the scale we go back to the 1st note C.

C major diatonic triads numbered

We now have all the notes that create each of the 7 triads. We know that the 1st triad is a C major chord but what about the others? It’s time to think about the distance between the notes in each triad. Here is a linear view of the notes from the C major chord on a guitar fretboard diagram.
C major triad notes guitar

A we can see there are 4 frets between the C note and the E note. This is 2 tones, also known as an interval of a major 3rd. Between the E and the G notes there are only 3 frets making 1 1/2 tones. This is called a minor 3rd interval.

All major chords are made up of a major 3rd and a minor 3rd. If we find any triads that follow this pattern they will be major chords. Apart from C there are two other major chords: one starting on the F and one on the G.

Here are the notes for the F major triad on a bass fretboard diagram.

F major triad notes bass

As you can see it follows the same pattern as the C major triad of a major 3rd and a minor 3rd. Here is the G triad on a banjo fretboard diagram. These also follow the major pattern.

G major triad notes banjo

Ok, so we’ve figure out the the C, F and G notes create major triads in the key of C. Many songs use these three chords and the majority of them will be in the key of C (there are always exceptions. Rules are meant to be broken sometimes!).

That leaves us with four chords to figure out. Lets have a look at the triad starting on the D note to see if we can figure out what kind of chord that is. Here is the D triad on a mandolin fretboard diagram.

D minor triad notes mandolin

The title of the diagram gives it away! It’s a minor triad. But why? If you remember from the constructing a minor chord lesson (have a quick look at the guitar, bass, banjo, mandolin or ukulele version) all you need to do is make the note from the chord based on the 3rd note of the major scale one fret lower. A D major chord has a D, F# and A note in it. The F in our triad is one note lower.

If we look at the distance between each note (the interval) we can see that they have switched around. There are 3 notes (1 1/2 tones) between the D and the F. This makes a minor 3rd interval. Whereas there are 4 frets (2 tones) between the F and A notes. This makes a major 3rd interval.

If we follow the minor chord formula of a minor 3rd then a major 3rd we will find 2 other chords that fit the pattern. These are based on the  E and A notes of the C major scale.

Here are the notes of the E minor triad on a ukulele fretboard diagram as an example.

E minor triad notes ukulele

So now we have 3 major chords and 3 minor chords. It just leaves us with one chord to figure out. Here are the notes of the B triad written out on a guitar fretboard diagram.

B diminished triad notes guitar

Again the title gives it away. This is a diminished triad. But what does that mean? Well you can see from the diagram that there is the same interval between the B and D and the D and F. They are both minor 3rds. All the other chords have a major 3rd (4 frets) and minor 3rd (3 frets) in them, just in different orders. This makes a total of 7 frets or 3 1/2 tones. The last note of the triad stays the same regardless of whether a chord is major or minor. It is the note in the middle (based on the 3rd of the major scale) that gives you the quality of the chord (major or minor).

For example, here are the triads for the D major and D minor.

D maj and min triad numbered

Both chords have D and A notes, it’s the note based on the 3rd note of the scale that changes the chord.

In a diminished chord the note based on the 5th is lowered by a fret or semi-tome. It’s a minor chord because of the minor 3rd interval between the B and D notes but has a extra sadness from the minor 3rd between the D and F notes.

Here are the triads for the B minor and the B diminished to show the difference.

B min and dim triad numbered

We now know all the chords that go with each note of a major scale. You can apply the following pattern to any major scale and find the chords for that key.

diatonic chord formula

Why not have a go a writing out the formulas for different keys. It’s good practice to write things down to help your brain to get around the theory!

There is a pdf version of this lesson available for you to download and keep as a reference.

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