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25: Diatonic Triads


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Lesson 25: Diatonic Triads

The diatonic triads are an important set of chords you can use to create your own chord progressions, and to understand chord progressions in songs. This lesson builds on many of our earlier lessons; you need to know major scales (Lesson 19: Major Scale 1-8), minor triads (Lesson 17: Minor Triads), upper scale degrees (Lesson 21: Scales Above 8), and Roman numeral chord symbols (Lesson 24: Roman Numeral Chords).

Diatonic means "staying within the key". So, for example, the diatonic triads in the key of B♭ major are the triads we can create using only pitches in the B♭ major scale.

There are just six "common" diatonic triads in any particular major key; we build these six triads on scale degrees 1 through 6 of the key's major scale. (We can also build a triad on degree 7, but that one is much less common, so I'm skipping it for now.) Let's find each of these six diatonic triads, one at a time:

The I chord ("one-major")


Our first diatonic triad uses degrees 1 3 5 of our (example) B♭ major scale:
12 34 5678
B♭C DE♭ FGA B♭
So, the pitches in this chord are B♭ D F; hopefully you recognize that this is a major triad (chord symbol: B♭); so our first triad's Roman symbol is just I ("one major").

The IIm chord ("two-minor")


The second triad uses degrees 2 4 6 of our B♭ major scale:
123 45 678
B♭CD E♭F GAB♭
So, the pitches in this chord are C E♭ G; this is a minor triad (chord symbol: Cm); so the Roman symbol is IIm ("two minor").

The IIIm chord ("three-minor")


The third triad uses degrees 3 5 7 of our B♭ major scale:
1234 56 78
B♭CD E♭FG AB♭
So, the pitches in this chord are D F A; this is a minor triad (chord symbol: Dm); so the Roman symbol is IIIm ("three minor").

The IV chord ("four-major")


The fourth triad uses degrees 4 6 8 of our B♭ major scale:
1234 567 8
B♭CD E♭F GA B♭
So, the pitches in this chord are E♭ G B♭; this is a major triad (chord symbol: E♭); so the Roman symbol is IV ("four major").

The V chord ("five-major")


The fifth triad uses degrees 5 7 9 of our B♭ major scale:
1234 56 78 910
B♭CDE♭ FG AB♭ CD
So, the pitches in this chord are F A C; this is a major triad (chord symbol: F); so the Roman symbol is V ("five major").

The VIm chord ("six-minor")


Finally, the sixth triad uses degrees 6 8 10 of our B♭ major scale:
12345 67 89 10
B♭CDE♭F GA B♭C D
So, the pitches in this chord are G B♭ D; this is a minor triad (chord symbol: Gm); so the Roman symbol is VIm ("six minor").

Summing Up


Putting it all together, in Roman chord symbols, these are the common major-key diatonic triads:

      I   IIm   IIIm   IV   V   VIm


And, for reference, here are they are as "specific" chords, in the common major keys:

Key I IIm IIIm IV V VIm
A♭ major A♭B♭m CmD♭E♭Fm
A major ABmC♯m DEF♯m
B♭ major B♭CmDm E♭FGm
B major BC♯m D♯mEF♯G♯m
C major CDmEm FGAm
D♭ major D♭E♭m FmG♭A♭B♭m
D major DEmF♯m GABm
E♭ major E♭FmGm A♭B♭Cm
E major EF♯m G♯mABC♯m
F major FGmAm B♭CDm
F♯ major F♯G♯m A♯mBC♯D♯m
G♭ major G♭A♭m B♭mC♭D♭ E♭m
G major GAmBm CDEm

When you understand these diatonic triads:
  • You can get suggestions for "practice activities" to help you learn to use them in the next lesson, Lesson 26: Using Diatonics;
  • Or, if you don't need practice suggestions, you can jump to learning about the different effects of the different diatonic triads in Diatonic Function.

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Lessons

1: Introduction
2: Teaching Yourself
3: Pitch & Keyboard
4: Pitch Names
5: Letters Game
6: Sharps & Flats
7: Half-Steps
8: Whole-Steps
9: Steps Game
10: Scales
11: Major Scale 1-2-3
12: Major 1-2-3 Games
13: Major Scale 1-5
14: Major 1-5 Games
15: Chords: Major Triads
16: Major Triad Games
17: Minor Triads
18: Minor Triad Games
19: Major Scale 1-8
20: Major Scale Games
21: Scales Above 8
22: What Next
23: Keys
24: Roman Numeral Chords
25: Diatonic Triads
26: Using Diatonics
27: 7th Chords
28: 7ths Games
29: Treble Staff
30: Treble Staff Game
31: Melody: Chord Tones
32: Pitch & Frequency

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