Diatonic chords

The key that a piece is written in does not just determine the possible melody tones, but also the chords that can be used.

The diatonic chords are the ones most likely to make an appearance. These are the chords that can be built on the tones of the key’s scale. They do not “borrow” tones from other scales.

Let’s assume we’re playing in the “key of C”. That means we’re using the tones from the C major scale.

The C major scale is: C D E F G A B C

We can build a three-note chord — also called a “triad” — on each of these tones.

This is the formula: We pick a root tone to start from, then skip one to find the second chord tone, then skip another to find the last chord tone.

The first chord is C major: C E G

See what I did? I started on the first tone from the scale, C. Then I skipped a tone, D, to land on E. Then I skipped another tone, F, to get to G. And I know that the combination C-E-G is called the “C major” chord.

The second chord is D minor: D F A

This time I started on D, skipped E, found F, skipped G, found A. Very simple.

If we apply that formula to all tones in the scale, we find the following chords:

Chord Tones
C major C E G
D minor D F A
E minor E G B
F major F A C
G major G B D
A minor A C E
B diminished B D F

Or viewed slightly differently:

C major C   E   G            
D minor   D   F   A          
E minor     E   G   B        
F major       F   A   C      
G major         G   B   D    
A minor           A   C   E  
B dim             B   D   F

Here it is in sheet music notation:

Diatonic triads of C major

For any piece in the key of C, these are the most common chords. (Actually, B diminished is much less common than the others.)

Not all of the chords have the same type: some are major, some are minor, and one is diminished.

For any major scale, the order is always as follows:

  1. major
  2. minor
  3. minor
  4. major
  5. major
  6. minor
  7. diminished

Try it for yourself on the scale of F major: F G A Bb C D E F

You should find the following chords:

Chord Tones
F major F A C
G minor G Bb D
A minor A C E
Bb major Bb D F
C major C E G
D minor D F A
E diminished E G Bb

Minor keys

We can also build chords on the tones from a minor key. Let’s take the key of A minor. We will use the natural minor scale to build the chords, except for one.

The natural scale of A minor is: A B C D E F G A

These are the same tones as the scale of C major, although in a slightly different order. That is because A minor is the relative minor of C major.

Because the two scales have the same tones, we can simply use the diatonic chords from the key of C major, but we now begin at A instead of C:

Chord Tones
A minor A C E
B diminished B D F
C major C E G
D minor D F A
E major E G# B
F major F A C
G major G B D

Pay attention to the 5th chord, E major. This is the exception. If we used the natural minor scale as we did for the other chords, this chord would have been called E minor.

Instead, we use the harmonic minor scale, which has a G# note instead of G. The reason is this: the 5-chord should have a strong, powerful sound, even in minor keys.

In sheet music notation the chords are:

Diatonic triads of A minor

Again, notice the G# on the E major chord.

Seventh chords

The chords we looked at so far were triads, chords with only 3 tones. We can add another tone on top to make them “seventh” chords. Adding this “7th” will refine the character of the chords.

(We could add more tones too, to make 9th, 11th, or even 13th chords, but these additional tones don’t have as much impact on the character of the chord.)

Back to the key of C and the C major scale: C D E F G A B C

We made our chords by skipping tones. Skipping another tone and adding the next note to our C major chord makes it a C major-7th or Cmaj7 for short: C E G B

The second chord then becomes Dm7 (D minor-7th): D F A C

Get the drift? Here are all the diatonic 7th chords:

Chord Tones
Cmaj7 C E G B
Dm7 D F A C
Em7 E G B F
Fmaj7 F A C E
G7 G B D F
Am7 A C E G
B half-dim7 B D F A

In sheet music:

Diatonic seventh chords of C major

Now what did I mean by “refining the character” of the chords? When we had just 3-tone chords, F and G were both major. Now, however, F has become a major-7 chord but G is a dominant-7 chord.

A major-7 chord and a dominant-7 chord have two very different functions in the language of music.

The 5th chord in the key, in this case G7, is therefore usually played as a four-tone chord, to make this distinction between major and dominant-7 clearer.

Like I said, the 5-chord is special.

Also, B diminished was refined to a B half-diminished-7 chord (and not a fully diminished-7 chord). Note that “Bm7b5″ is another way of writing “B half-dim7″.

The order of diatonic seventh chords in a major key is always:

  1. maj7
  2. m7
  3. m7
  4. maj7
  5. dominant-7 (or just “7”)
  6. m7
  7. half-dim7 (or “m7b5″)

We can also add 7ths to the chords from a minor key:

Chord Tones
Am7 A C E G
B half-dim7 B D F A
Cmaj7 C E G B
Dm7 D F A C
E7 E G# B F
Fmaj7 F A C E
G7 G B D F

Again, these are simply the chords from C major in a different order. With the exception of the the 5-chord, E7, which has also become a dominant-7 chord here.

Read more articles on Piano Clues:

Basic Theory

Chords and Harmony

The Circle of Fifths

Arrangement, Improvisation and Composition

Reading Music and Sheet Music

How to Record Piano

Software and Virtual Instruments

Scales and Exercises

Digital Pianos

Links and Other Stuff


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