Diatonic Chords

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Chapter 5 · Lesson 04

In short

If you build a triad on every degree of a scale, using only its notes, you get the diatonic chords. In the major scale their quality always follows the same pattern.

Lesson Notes

You know how a chord is built and what types exist. Now you place a chord on every degree of the scale, and see what comes out.

01A chord on every degree

On each degree you stack two thirds, using only notes of the scale. You add no accidentals and you don't "borrow" notes from anywhere else. That way every degree gets its own triad.

These seven chords are called diatonic, because they come exclusively from the notes of the scale (diatonic = within the key, inside the scale). Every major or minor scale has its own family of seven such chords.

02The major scale's pattern

In C major the seven diatonic chords come out like this: I is major, ii is minor, iii is minor, IV is major, V is major, vi is minor, and vii° is diminished.

The Roman-numeral notation shows the quality at a glance: uppercase (I, IV, V) for major chords, lowercase (ii, iii, vi) for minor ones, and the ° symbol for the diminished one (vii°).

The diatonic chords of C major

The pattern maj. · min. · min. · maj. · maj. · min. · dim. holds for every major scale, not just C.

The seven chords with their qualities:

I · C-E-G · major chord
ii · D-F-A · minor chord
iii · E-G-B · minor chord
IV · F-A-C · major chord
V · G-B-D · major chord
vi · A-C-E · minor chord
vii° · B-D-F · diminished chord

03The three essentials: I, IV, V

Of the seven, three stand out as the main ones. The tonic (I) is the scale's "home", the point of rest. The subdominant (IV) provides contrast without straying far. The dominant (V) creates tension that asks to resolve to the tonic. Together, these three cover the harmonic skeleton of countless songs.

Add the vi (the minor chord on the 6th degree) and you get the progression I-V-vi-IV, one of the best-known harmonic patterns worldwide. That is no accident: these four chords cover the major scale's three pillars (tonic, dominant, relative minor).

04In the minor scales too

The same thing happens in the minor scales: you stack a chord on every degree. The difference is that the minor has three forms, the natural, the harmonic and the melodic, and each form gives slightly different chords. Let's take A minor, the relative of C major, as our example.

In the natural minor the notes are the same as in the relative major, so the same seven chords come out, just starting from a different degree. The tonic (i) is now minor.

In the harmonic minor we raise the 7th degree by a semitone (G → G♯), so that the scale gains a leading tone. That one note makes the V major (the dominant), and so the V-i cadence becomes much stronger. At the same time the III becomes augmented (III+, the + marks an augmented chord) and the vii becomes diminished.

In the melodic minor we raise both the 6th and the 7th degree, so even more chords change: the IV becomes major too.

The diatonic chords of A minor

FormRaised degreesChords (i-vii)

Naturalnonei · ii° · III · iv · v · VI · VII

Harmonic7thi · ii° · III+ · iv · V · VI · vii°

Melodic6th, 7thi · ii · III+ · IV · V · vi° · vii°

The most useful change is in the harmonic form: the raised 7th turns the dominant (v) into a major chord (V), which gives a stronger cadence to the tonic.

Recap

Stack two thirds on every degree of the scale, using only its notes: you get the diatonic chords.
In the major scale the quality follows a fixed pattern: I IV V major, ii iii vi minor, vii° diminished.
Uppercase = major, lowercase = minor, ° = diminished.
I, IV, V are the major scale's harmonic skeleton. Adding the vi gives the I-V-vi-IV progression.
The pattern holds for every major scale, not just C.
The minor scales have three forms (natural, harmonic, melodic) with slightly different diatonic chords. Raising the 7th degree (harmonic) makes the V major, for a stronger V-i cadence.