Seventh Chords

A seventh chord is a triad with one more note stacked on top: the 7th degree above the root. 1 3 5 becomes 1 3 5 7.

Take the C major triad C E G. Keep stacking in thirds: the next note above G is B, the 7th degree of C major, a major seventh above the root. C E G B is Cmaj7. Shrink that top interval to a minor seventh, Bb, and you get C7, a chord with a completely different pull.

That fourth note is the whole point of this chapter. The kind of 7th you add (7, a major seventh, or b7, a minor seventh) combined with the kind of triad underneath (major, minor, diminished) gives each seventh chord its own name and its own character.

The major seventh chord (maj7) is a major triad with the natural 7th on top: 1 3 5 7. The 7 is a major seventh above the root. It sounds warm, open and settled: a resting chord with extra colour.

The major seventh is the widest interval in the chord: B sits right under the octave C, just a semitone short of it. Played alone, B against C clashes; inside the full chord it turns into a soft glow instead. In a key, maj7 chords live on I and IV, the two most stable places.

The minor seventh chord (m7) is a minor triad with a lowered 7th: 1 b3 5 b7. The b7 is a minor seventh above the root. It is smooth and mellow: minor, but softer than a bare minor triad.

Both the 3rd and the 7th are lowered, so the chord has no sharp edges: the minor seventh sits a whole tone below the octave, not a semitone. In a major key, m7 chords sit on ii, iii and vi; in a minor key the tonic itself is a m7 chord (i7).

The dominant seventh chord (written just 7, as in G7) is a major triad with a lowered 7th: 1 3 5 b7, a major third and a minor seventh on the same root. It is the chord of tension: it wants to move.

Why so restless? Look at the 3 and the b7: in G7 they are B and F, a tritone apart (an augmented fourth, six semitones), the most unstable interval there is. The rest of the chord is a plain major triad; the tritone is the engine.

It is called *dominant* because in a key this quality appears naturally on degree 5, the dominant (V7). G7 is the V7 of C major, and it pulls straight back to C.

The m7b5 chord, also called half-diminished (symbol ø7), is a diminished triad with a minor 7th: 1 b3 b5 b7. Minor third, diminished fifth, minor seventh. Dark, unstable, and made for leading somewhere.

It is a minor seventh chord with the 5th lowered, hence the name m7b5. In a major key it sits on vii (Bm7b5 in C major); in a minor key it sits on ii (Bm7b5 in A minor). That second role is the important one: it opens the minor ii-V-i.

The diminished seventh chord (dim7, symbol °7) lowers the 7th twice: 1 b3 b5 bb7. The bb7 is a diminished seventh above the root, one step smaller than the minor seventh. Every note is a minor third above the last: a perfectly even, perfectly tense chord.

The bb7 is a *double* flat: Bbb sounds like A, but we spell it as a kind of B so the chord is still built in thirds. Compare it with Cm7b5: only the top note differs, Bb versus A, a minor seventh versus a diminished seventh, and that one change takes the chord from dark to fully diminished.

Put all five qualities on C and you can hear that they form a ladder: each step down shrinks exactly one interval by one quality. A major seventh becomes minor, a major third becomes minor, a perfect fifth becomes diminished, a minor seventh becomes diminished.

Play them in order and listen to the mood darken one notch at a time: settled, then pulling, then mellow, then unstable, then fully tense. Learn to hear these five and you can name almost every seventh chord in a song.

Build a seventh chord on every degree of a major scale, using only the scale's notes, and the qualities always come out in the same order: Imaj7 ii7 iii7 IVmaj7 V7 vi7 viim7b5.

Notice there is exactly one dominant 7th in the key, on V. That is what makes G7 unmistakably point to C: no other diatonic chord has that tritone. In G major the same pattern gives Gmaj7 Am7 Bm7 Cmaj7 D7 Em7 F#m7b5.

Do the same on the natural minor scale 1 2 b3 4 5 b6 b7 and the qualities come out as i7 iim7b5 IIImaj7 iv7 v7 VImaj7 VII7: the major-key pattern rotated to start from its sixth chord.

There is a catch: the natural v7 (Em7) is a minor chord with no leading tone, so it resolves to Am only weakly. Standard practice in minor keys, in classical, pop and jazz alike, is to raise the 7th degree (G → G#) as in the harmonic minor scale, turning the chord into a real dominant: V7 = E7 (E G# B D). The same raised note gives viidim7 = G#dim7.

The most common seventh-chord progression is ii7 to V7 to Imaj7: a minor 7th leading to the dominant, which leads home. In C major that is Dm7-G7-Cmaj7.

Each chord hands notes to the next. Dm7 (D F A C) shares D and F with G7 (G B D F); G7 then releases its tritone into Cmaj7. The ii chord is a preparation: it makes the arrival of V7 feel expected, and V7 makes the arrival of I feel inevitable.

In a minor key the same progression uses the chords we just found: iim7b5 to V7 to i7. In A minor: Bm7b5-E7-Am7. The half-diminished ii and the harmonic-minor V7 are what make it sound unmistakably minor.

When V7 resolves to I, two notes do the work: the 7th of the chord falls one step onto the 3rd of the tonic, and the leading tone rises by a semitone onto the tonic itself.

That is the tritone B-F closing inward onto C-E: the two most unstable notes of the key land on the two most stable ones. Get these two motions right and any V7 → I sounds resolved, whatever you do with the other notes.

Seventh chords are written with a few standard symbols, and you will meet several spellings for the same chord. Here is the cheat sheet.

Read the symbol as *triad + 7th*: a bare 7 means major triad with b7; maj7 means the natural 7; m before anything means the b3. In this course we write m7b5 for half-diminished and dim7 for fully diminished.

And the stacking does not stop at four notes. Keep adding thirds above the 7th and you reach the 9th, 11th and 13th (1 3 5 b7 9, 1 3 5 b7 9 11 13), the extended chords of jazz and R&B. They are built on exactly the seventh chords you now know. Before we go there, the next chapter takes a different turn: the modes, seven scales hidden inside the major scale, each with its own colour.