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23: Diatonic Triads

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Lesson 23: Diatonic Triads

This lesson teaches diatonic triads, which are important for understanding the chords used in many songs (or writing your own songs).

Before taking this lesson, you should know:
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 24: 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 Lesson 25: Tonic Function.

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Lessons

1: Introduction
2: Practicing Songwriting
3: Pitch Names
4: Letters Game
5: Sharps & Flats
6: Half-Steps
7: Whole-Steps
8: Steps Game
9: Scales
10: Major Scale 1-2-3
11: Major 1-2-3 Games
12: Major Scale 1-5
13: Major 1-5 Games
14: Chords: Major Triads
15: Major Triad Games
16: Minor Triads
17: Minor Triad Games
18: Major Scale 1-8
19: Major Scale Games
20: Keys
21: Roman Numeral Chords
22: Scales Above 8
23: Diatonic Triads
24: Using Diatonics
25: Tonic Function
26: Subdominant & Dominant
27: Diatonic Function Analysis
28: Natural Minor Scale
29: Natural Minor Games
30: Minor Key Triads
31: 7th Chords
32: 7ths Games
33: Melody: Chord Tones
34: Treble Staff
35: Treble Staff Game
36: Time: Beats & Measures
37: Note Lengths
38: Tied & Dotted Notes
39: Rhythm: Rests
40: Non-Root-Bass Chords
41: Major Pentatonic Scale
42: Embellishing Tones
43: Melody Rhythm: Rolling Stone
44: Pitch & Frequency

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