Duration: 4:29 · 1080p Stream
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Why some chords "belong" to a key. You'll learn how the major scale is built (whole-whole-half-whole-whole-whole-half) and how stacking thirds on each scale degree produces the diatonic chords — major on the I, IV, and V; minor on the ii, iii, and vi; diminished on the vii. That mapping from scale degree to chord quality is the backbone of harmony and well worth memorizing, and a quick look at the diatonic 7th chords rounds out the picture.
What follows is this lesson’s section of the Course Guide — you can read it here or in the full guide →
Diatonic chords are chords that are created from an underlying scale, which means that every note in every diatonic chord is in the scale.
The major scale is built out of major second (whole-step) and minor-second (half-step/semitone) intervals.
Memorize this: The sequence of two- and one-fret intervals inside the major scale is an essential building block. It is also worth remembering how the interval names come from the scale degrees of the notes in the major scale:
Since the major scale repeats after seven notes, there are exactly seven different diatonic triads that can be created by starting on a scale degree, taking that note as the root, skipping one scale degree and selecting the next note as the third, and then skipping one more scale degree and selecting the next note as the fifth.
Memorize this: If you start on the first, fourth, or fifth scale degree of the major scale, you will build a major triad. You get a minor triad if you start on the second, third, or sixth scale degree. If you start on the seventh scale degree, you get a diminished triad.
Triad type Scale degree
(major scale)Interval spelling major 1, 4, 5 1 3 5 minor 2, 3, 6 1 b3 5 diminished 7 1 b3 b5
It’s also worth knowing these formulas for seventh chords, but you won’t need them for this course:
| Chord type | Scale degree (major scale) | Interval spelling |
|---|---|---|
| maj7 | 1, 4 | 1 3 5 7 |
| m7 | 2, 3, 6 | 1 b3 5 b7 |
| 7 | 5 | 1 3 5 b7 |
| m7b5 | 7 | 1 b3 b5 b7 |
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