Sevenths: The Next Note Up
The first theory path built chords by stacking thirds: take a scale note, add the note two steps up, add another. Three notes, a triad. This one starts by adding a fourth note — one more third on top — and that single addition explains an enormous amount about how real songs sound.
The fourth note is a seventh above the root, so these are called seventh chords. What makes them worth studying is that they are not all the same kind. Build a seventh chord on each degree of the major scale, using only notes from that scale, and three distinct flavours come out in a fixed pattern.
In the key of C, here is the whole set.
Cmaj7
C major seventh, the I chord. A major triad with a major seventh added — the sound is warm and unresolved rather than tense.
Dm7
D minor seventh, the ii chord.
Em7
E minor seventh, the iii chord.
Fmaj7
F major seventh, the IV chord. The same flavour as the I chord.
G7
G seventh, the V chord — and the only one of the seven that comes out like this.
Am7
A minor seventh, the vi chord.
Bm7♭5
B minor seven flat five, the vii chord. Also called half-diminished, and the odd one out.
Read the pattern down the list: major seventh, minor seventh, minor seventh, major seventh, dominant seventh, minor seventh, half-diminished. That order is the same in every major key. It is worth memorising, because it lets you name any chord in any song by position alone.
The important one is the fifth. A plain dominant seventh chord — a major triad with a flattened seventh — occurs in exactly one place in the key, on the fifth degree. That uniqueness is why it does so much work. When you hear a dominant seventh, your ear can identify which key you are in, because there is only one chord like it per key and it points straight at the root a fifth below.
That is also the reason a dominant seventh sounds unstable in a way a major seventh does not. It contains a tritone — the interval between its third and its seventh, B and F in a G7 — and the tritone is the most restless interval in the system. It wants to resolve, and the place it resolves to is the I chord.
Soft Summer Bossa – Smooth Jazz Backing Track in C Major (108 bpm)
A bossa in C major whose harmony leans heavily on these chords. Listen for how much smoother major sevenths and minor sevenths sound than plain triads would.