And these are the Seven Diatonic Chords of a Key!
What are diatonic chords?
I am always struck by how many musicians are still completely confused or clueless about the importance of diatonic chords and how chords are related to each other within a key.
Simply put, diatonic chords are chords that belong and come from the same scale. Most classically-trained pianists know how to play their major and minor scales very well. But some may not understand the significance of the chords that are associated with the scale.
Let’s take a look at a C Major Scale:
If we stack another two notes a third apart (skip a key each on the keyboard) above each scale note, we immediately form the seven (7) diatonic triads of the C Major scale or key.
If we give a number to each chord of the scale (we usually use Roman numerals to represent chords, e.g. I, II, III, etc.; Arabic numerals to represent scale notes, e.g. 1, 2, 3, etc.), we will have the following chords from this C Major scale:
|Chord No.||Chord||Chord No.||Chord|
Notice that the I, IV and V chords, i.e. C, F and G are all major quality chords. The chord symbol is just represented by a capital letter.
The II, III and VI chords, i.e. Dmi, Emi and Ami are minor quality chords. The chord symbol may be represented as a capital letter along with mi, min or – (minus sign.)
Lastly, the VII chord, i.e. Bdim is a diminished quality chord. The chord symbol may be represented as a capital letter along with dim or a degree sign.
Once you understand this concept in one key, it will apply to all keys. Hence, if you take the key of G major, you will find these seven diatonic triads:
Notice they all have the same chord quality sound and chord symbols according to the position in the major scale!
Why are these diatonic chords important?
Every melody note comes from a scale that forms the key of the song. Hence, it is only logical that the chords that go well with the melody will also come from the same scale!
Let’s take the old favorite “Twinkle, Twinkle, Little Star.”
The melody uses the first six notes of the C Major scale. Hence, we can safely say that this melody is in the Key of C.
Now, in order to put chords to (or harmonize) this melody, we simply start by looking at the seven C Major diatonic chords. If we do it systematically you will find the following:
|Melody note||Available chords||Melody note||Available chords|
|C||C, F, Ami||F||F, Dmi, Bdim|
|D||G, Dmi, Bdim||G||C, G, Emi|
|E||C, Emi, Ami||A||F, Dmi, Ami|
Notice each melody note has at least three chords that contain that note.
Notice also that both major and minor chord qualities are available for each note. Melody notes D and F can also be harmonized with a diminished quality chord.
Interestingly, you will observe that the C, F and G major chords, i.e. I, IV, V seem to feature prominently in the choices. That is because major chord qualities are considered strong chords or primary chords in harmonization, i.e. they get first priority, followed by the minor chords which are considered secondary chords. The major and minor chords are always considered the strong choices — major being the strongest of the two.
Hence, the best and simplest harmonization for this song is as follows:
Primary triads of I, IV and V also contain all the seven notes of a major scale. In other words, the seven notes of a major scale can easily be found in any of the three chords.
So it’s worthwhile mastering this fundamental harmonic concept of diatonic triads. Learn and play them in all keys!