In our last lesson, we looked at the harmonization of the major scale using triads (three-note chords). Today, we’re going to take things one step further by adding one more note on top — giving us seventh chords.
Seventh chords are incredibly common in jazz, pop, and rock, and understanding how they’re formed will help you unlock richer, more colourful harmonies in your playing.
From Triads to Seventh Chords
A triad is built by stacking two notes in thirds. For example, in the key of C major:
- Start with C
- Skip D, add E
- Skip F, add G
That gives us C–E–G, a C major triad (1–3–5).
To create a seventh chord, we keep stacking one more note:
- Skip A, add B
Now we have C–E–G–B, which forms a C major 7 chord (1–3–5–7).
Seventh Chords in the Key of C Major
If we harmonize the entire C major scale by stacking four notes on each degree, we get:
- Cmaj7 (C–E–G–B)
- Dm7 (D–F–A–C)
- Em7 (E–G–B–D)
- Fmaj7 (F–A–C–E)
- G7 (G–B–D–F) → dominant seventh
- Am7 (A–C–E–G)
- Bm7♭5 (B–D–F–A) → half-diminished
Why Is the 5 Chord a Dominant 7th?
Notice that the 5 chord (G) isn’t a major 7 but a dominant 7 (G7).
- If we stacked G–B–D–F♯, it would be Gmaj7.
- But the C major scale doesn’t have F♯ — it has F natural.
So the chord becomes G–B–D–F, which is a G dominant 7th (1–3–5–♭7).
This chord is hugely important in music because it naturally resolves back to the I chord (C major). That’s why it’s called the “five chord” or V7 chord.
The Tricky One: The 7th Chord (B)
In the triad version, the 7th chord is B diminished (B–D–F).
When we extend it to a four-note chord, we get B–D–F–A, which is called:
- B half-diminished (Bm7♭5) → 1–♭3–♭5–♭7
This chord is less common in pop music but is essential in jazz and classical harmony.
The Complete List of Diatonic Seventh Chords in C Major
To recap, here’s the full set:
- I (Cmaj7) → Major 7
- ii (Dm7) → Minor 7
- iii (Em7) → Minor 7
- IV (Fmaj7) → Major 7
- V (G7) → Dominant 7
- vi (Am7) → Minor 7
- vii° (Bm7♭5) → Half-diminished
Why This Matters for Guitarists
Seventh chords add depth and emotion to your playing. They appear everywhere — from jazz standards to R&B grooves to pop ballads.
For example:
- Instead of playing C–Am–F–G, try Cmaj7–Am7–Fmaj7–G7.
- The difference in richness and smoothness is immediately noticeable.
FAQ: Seventh Chords
Q: What’s the difference between major 7 and dominant 7?
- Major 7 uses the natural 7th (e.g. C–E–G–B).
- Dominant 7 uses a flat 7th (e.g. G–B–D–F).
Q: Why is the 7 chord half-diminished?
Because stacking four notes on B (B–D–F–A) gives us a diminished triad plus a flat 7, which is the definition of a half-diminished chord.
Q: How do I practice this on guitar?
Play the C major scale chords as sevenths up and down the neck. Start with simple shapes (Cmaj7, Dm7, etc.), then use them in progressions.
Final Thoughts
By extending triads into seventh chords, you unlock a much richer harmonic vocabulary. These chords are everywhere in modern music — whether you’re strumming pop progressions, comping jazz, or exploring songwriting.
Next time you play a progression, try swapping in seventh chords instead of plain triads. Your playing will instantly sound more sophisticated.