Lesson 4 of 7 · about 15 minutes

Chords: Triads, Sevenths and the Chords in a Key

You'll be able to

Spell a major, minor and dominant seventh chord on any root
Build the seven chords of a major key by stacking thirds
Name the I, IV, V, ii, iii and vi chords in common keys
Explain why the V7 chord pulls back to I

A chord is three or more notes played together. The basic chord, the one under almost every folk song, has exactly three notes and is called a triad. Build one and you have built them all, because every triad is two thirds stacked on top of each other.

Major and minor triads

Start on a note, called the root. Go up a third. Go up another third. Done.

The two kinds of third from lesson 3 decide the flavor:

Major triad: root, up a major third (4 half steps), then up a minor third (3 half steps). C major is C, E, G.
Minor triad: root, up a minor third (3 half steps), then up a major third (4 half steps). C minor is C, Eb, G.

Both span a perfect fifth from bottom to top, 7 half steps. The only difference is the middle note. Move the third down a half step and a happy chord turns sad. You can hear it on a guitar right now: play an open E major chord, then lift your first finger off the third string. That one note drops from G# to G and you are playing E minor.

Root	Major	Minor	Dominant 7
C	C, E, G	C, Eb, G	C, E, G, Bb
G	G, B, D	G, Bb, D	G, B, D, F
D	D, F#, A	D, F, A	D, F#, A, C
A	A, C#, E	A, C, E	A, C#, E, G
E	E, G#, B	E, G, B	E, G#, B, D
F	F, A, C	F, Ab, C	F, A, C, Eb
B	B, D#, F#	B, D, F#	B, D#, F#, A

A six-string guitar chord has more than three strings ringing, but it still holds only three different note names. An open G chord on guitar plays G, B, D, G, B, G from low to high (or G, B, D, G, D, G in the common fingering with the B string fretted at the third fret). Doubled notes, same triad.

Seventh chords

Add one more third on top of a triad and you get a seventh chord. Folk and country use one kind far more than the rest: the dominant seventh, written with a plain 7. It is a major triad plus the note a minor seventh (10 half steps) above the root.

G7 is G, B, D, F. Look closely: F, not F#. This is the most common spelling mistake in chord theory, so slow down on it. The 7 in "G7" means the flat seventh, the bluesy one.

Cousins you will see on charts:

Major seventh (Cmaj7): a major triad plus the note a major seventh up, 11 half steps. Cmaj7 is C, E, G, B. Soft and dreamy. More common in 1970s singer-songwriter music than in bluegrass.
Minor seventh (Am7): a minor triad plus a minor seventh. Am7 is A, C, E, G. Mellow. Shows up a lot in gospel and soul-tinged country.

A plain "7" means dominant seventh: major triad plus a flat seventh. G7 has an F natural. "maj7" is the one with the F#.

The chords that live in a key

Here is the idea that makes songwriting theory click. Take a major scale. On each note of it, stack thirds using only notes from that scale. You get seven chords, and they are the chords that naturally belong to that key.

Example: the chords in C major

C major scale: C, D, E, F, G, A, B. Stack every other note.

On C: C, E, G. C major.
On D: D, F, A. D minor.
On E: E, G, B. E minor.
On F: F, A, C. F major.
On G: G, B, D. G major.
On A: A, C, E. A minor.
On B: B, D, F. B diminished.

Look at the pattern of qualities: major, minor, minor, major, major, minor, diminished. That pattern is the same in every major key, because every major scale has the same step pattern. So you can memorize it once.

Theory writes these chords with Roman numerals. Capitals mean major, lowercase means minor, and a small circle (or "dim") marks diminished:

I    ii    iii    IV    V    vi    vii°

Now apply the pattern to the guitar-friendly keys. Every chord here comes from the scale table in lesson 2, and I spelled each one out to check it.

Key	I	ii	iii	IV	V	vi	vii°
C	C	Dm	Em	F	G	Am	Bdim
G	G	Am	Bm	C	D	Em	F#dim
D	D	Em	F#m	G	A	Bm	C#dim
A	A	Bm	C#m	D	E	F#m	G#dim
E	E	F#m	G#m	A	B	C#m	D#dim
F	F	Gm	Am	Bb	C	Dm	Edim

The six chords that write most songs

The vii° chord almost never shows up in folk or country. That leaves six, and three of them do most of the work.

I is home. Songs start here and end here.
IV is the step away. It feels like leaving the porch. In gospel it is the "amen" chord: IV back to I is the sound of a church ending.
V is tension. It wants to go home to I. That pull is the engine of nearly every country song ever cut.
vi is the relative minor. It is home's sad twin, sharing two notes with the I chord. Use it when the story turns.
ii is a soft minor that loves to lead into V. The ii to V to I move is all over Western swing and older pop standards.
iii is the least used. It can stand in for I or lead to vi.

With just I, IV and V you can play thousands of songs. Hank Williams wrote a career on them. Add vi and you get most of modern country radio. Nobody should call that lazy. Three chords leave room for the words, and in a protest song or a story song, the words are the point.

Why V7 pulls so hard

Turn the V chord into a dominant seventh and the pull home gets stronger. In the key of G, the V7 is D7: D, F#, A, C. Two of those notes are restless. F# sits a half step under G and wants to rise to it. C sits a half step above B and wants to fall to it. And G and B are in the G chord. So D7 to G feels like two magnets snapping together. Those two notes, F# and C, are six half steps apart: the tritone from lesson 3.

That is why the last chord before the final G in so many hymns and country songs is a D7. You can write V7 on any chart and every player will know to add the seventh.

Try it

Spell A major, A minor and A7 on paper by counting half steps. Then check against the table.
Build the seven chords of D major yourself by stacking thirds from the D major scale (D, E, F#, G, A, B, C#). Confirm the quality pattern major, minor, minor, major, major, minor, diminished.
Play G, then C, then D, then G on a guitar. Now play G, C, D7, G. Listen for the stronger pull home with the seventh.
Play an E major chord and let it ring. Record it into SoundStudio. Then hum each of the three chord tones one at a time (E, G#, B) and read them on the pitch line in the Wave + Pitch view. Do the same for E minor (E, G, B) and notice that only the middle note moved, down one half step.

Checklist

I can spell major and minor triads by stacking thirds.
I know G7 has an F natural and Gmaj7 has an F#.
I know the quality pattern of a major key: I ii iii IV V vi vii°.
I can name the I, IV, V and vi chords in G, D, A, C and E.

Current: In the News

Listed for reference, not as endorsements. Checked October 2026.

Audio and video

"Chords in Major and Minor Keys - TWO MINUTE MUSIC THEORY #47", Jesse Strickland (YouTube), June 6, 2019. Short explainer on diatonic chords, the seven chords built from a key.
"Developing Your Musicianship", Berklee on Coursera. Berklee video course with modules on major and minor triads, I IV V, and major and dominant seventh chords.

External resources

"Diatonic Triads", musictheory.net. Interactive lesson building a triad on each scale degree, matching the I, ii, iii, IV, V, vi pattern.
"Seventh Chords", musictheory.net. Shows how a fourth note turns a triad into a seventh chord, including the dominant seventh.
"Triads", Open Music Theory. Open textbook chapter on triad qualities and where each falls in major and minor keys.
"Seventh Chords", Open Music Theory. Explains the five common seventh chord qualities and the dominant seventh's role.
"Chord Ear Training", musictheory.net. Free drill for hearing the difference between major, minor and seventh chords.

Check yourself

1. What notes make a D major chord?

2. In the key of G, which chord is the vi?

3. What note does a G7 chord add to a G major chord?

4. In any major key, which three chords are minor?

5. In the key of A, what are the I, IV and V chords?

6. Why does a V7 chord sound like it wants to go to I?

Terms in this lesson

Chord: Three or more notes sounded together.
Triad: A three-note chord built from a root, a third and a fifth.
Root: The note a chord is named after and built up from.
Dominant seventh: A major triad plus the note a minor seventh above the root. Written as a plain 7, such as G7 or D7.
Roman numerals: A way to name chords by their place in the key. Capitals for major (I, IV, V), lowercase for minor (ii, iii, vi).
Diminished: A triad made of two minor thirds stacked, such as B, D, F. Tense and rare in folk songs.

Full glossary