So far every chord has been a triad — three notes. Two small additions turn that raw material into finished music: a seventh on top for extra tension, and cadences — the two-chord endings that punctuate a phrase like a comma or a full stop.
Add a seventh
A triad stacks two thirds (1·3·5). Keep stacking thirds and the next note up is the 7th. Add it and you have a seventh chord — richer, and hungrier to resolve. Build one on G, the V chord of C major:
G7 = G · B · D · F. The plain G triad already creates dominant tension; the added F cranks it up. Written as a roman numeral this is V7 — the single most important seventh chord in tonal music.
Why V7 pulls home so hard
The magic is a tritone — a maximally tense interval — hiding between two of G7's notes:
- B is the leading tone of C. It sits a half step under the tonic and aches to rise to C.
- F is the new seventh. It sits a half step above E and wants to fall to it.
Those two notes, B and F, are a tritone apart — and when the chord resolves, they collapse inward at the same instant:
| Tense note | Moves | Lands on |
|---|---|---|
| B (leading tone) | up a half step | C |
| F (the 7th) | down a half step | E |
Both arrivals — C and E — are notes of the C chord. Two half-step pulls resolving together is why V7 → I snaps shut so satisfyingly. A plain V has only one of those pulls; V7 has both.
In short. The 7th adds a second half-step tension, turning V's single pull toward home into a double one. That's why so many songs reach for V7 — not just V — right before the finish.
Cadences: harmony's punctuation
A cadence is the pair of chords that ends a phrase. Just as punctuation shapes a sentence's rhythm, cadences tell the ear whether a musical line has finished, paused, or taken a surprise turn. Four are worth knowing (all shown in C):
| Cadence | Chords | Punctuation | Feel |
|---|---|---|---|
| Authentic | V → I | full stop . | complete, fully resolved (V7 → I is strongest) |
| Plagal | IV → I | gentle stop | the warm "amen" ending |
| Half | …→ V | comma / question ? | unfinished — leaves you hanging on the tension |
| Deceptive | V → vi | plot twist ! | you expected home, got its darker cousin |
The authentic cadence is the strong one — the tritone resolution you just saw:
The half cadence does the opposite: it stops on the tension of V, asking a question that begs for an answer:
And the deceptive cadence sets up a full stop, then dodges it — resolving V to vi (home's substitute) instead of I:
Putting it together: call and response
Cadences let a song breathe. Open a phrase with a half cadence — a question — then answer it with an authentic cadence — the reply:
That question-and-answer shape — half cadence out, authentic cadence back — is the backbone of countless four-bar melodies. Want to keep a song going? Slip a deceptive cadence in first, then finally close with the real authentic one.
In one line: a seventh adds colour and — in V7 — a tritone that pulls doubly home, while cadences punctuate phrases: authentic (full stop), plagal (amen), half (question), deceptive (twist).