Diatonic Harmony (The Family of Chords)

You cannot just pick random chords and expect them to become a song. You must pick chords that “live” in the same key. This is called Diatonic Harmony.

16.1 The Rule of Families

Every Major Scale creates a family of 7 specific chords.

• The Rule: We build a triad on top of every single note of the Major Scale, using only the notes from that scale.

Let’s look at the Key of C Major (No sharps, no flats):

1. C (C-E-G) -> Major
2. D (D-F-A) -> Minor
3. E (E-G-B) -> Minor
4. F (F-A-C) -> Major
5. G (G-B-D) -> Major
6. A (A-C-E) -> Minor
7. B (B-D-F) -> Diminished

16.2 The Roman Numeral System

Musicians use Roman Numerals to talk about chords because it applies to any key.

• Capital Numerals (I, IV, V): Major Chords.
• Lowercase Numerals (ii, iii, vi): Minor Chords.
• Degree symbol (vii°): Diminished Chord.

The Universal Pattern: No matter what key you are in (C, F#, Bb), the pattern of chords is always the same: I (Major) — ii (minor) — iii (minor) — IV (Major) — V (Major) — vi (minor) — vii° (diminished)

• This is why the “Axis of Awesome” 4-chord song works: almost every Pop song uses I, V, vi, IV.