Triads & Seventh Chords
Stacking thirds
A chord is a few notes played together, and the basic chord of Western music is the triad, which means three notes. But you cannot just grab any three notes. A triad is built by stacking, skipping one letter each time you go up.
Start on a note, skip the next letter, land on the one after, then skip again. Starting on C you take C, skip D, land on E, skip F, land on G. That gives C, E, G, a triad. The three notes are called the root (the bottom, which names the chord), the third, and the fifth.
At a keyboard, play C, E, and G together. That full, agreeable sound is a triad, three stacked notes ringing at once.
A triad is a three-note chord built by stacking two thirds. Take a root note, add the note a third above it, then add another note a third above that. Measured from the root, those three notes are the root, the third, and the fifth, which is where the names come from: the third is a third above the root, the fifth is a fifth above it.
The gaps are always thirds, meaning you skip one letter name each step. On C that is C to E and E to G; on G it is G to B and B to D. Because the skeleton is fixed as root, third, fifth, every triad has the same shape, and only the exact size of each third changes from one chord to the next, which is what the following parts sort out.
Western harmony is built on the interval of a third, and the triad is the smallest complete chord that interval produces. A stack of thirds gives a full sound whose three notes the ear can still pick apart, and centuries of practice settled on it as the basic unit of harmony.
The stacked-thirds design also explains why the root, third, and fifth do different jobs. The root anchors the chord and gives it its name; the third in the middle decides much of its color; the fifth reinforces the root from above. Nearly every chord in the classes ahead is this three-note frame with more thirds added or its notes reordered.
Stacking thirds
How is a triad built?
Major and minor triads
Not all triads sound the same. The two you meet most are the major triad, which sounds bright and happy, and the minor triad, which sounds darker and sadder, the same bright-and-dark feeling you met with scales.
The difference is the middle note. A C major triad is C, E, G, and it sounds cheerful. Lower that middle E by a half step to E-flat and you get C, E-flat, G, a C minor triad, which sounds gloomier. The bottom and top notes stayed put; only the third moved, and the whole mood changed.
Play C-E-G, then play C-E-flat-G. Listen to the mood flip from sunny to shadowy with that one small change in the middle.
The major and minor triads differ only in the third. A major triad stacks a major third (four half steps) then a minor third (three half steps), so C major is C, E, G. A minor triad reverses that order, a minor third then a major third, so C minor is C, E-flat, G. Both span a perfect fifth from root to top; only the third sits in a different spot.
That one note is why they sound so different. Because the third is what the ear reads as major or minor, moving it a half step swaps the whole quality while the root and fifth hold steady. Learn to hear and build both from any root, because major and minor triads are by far the most common chords in tonal music.
The third alone decides major or minor because both triads share the same root and fifth. The fifth above the root is one of the first and most consonant intervals in the overtone series, so it frames both the bright and the dark triad while staying neutral between them, leaving the third to set the color.
Major and minor are mirror images, one third order and its reverse, which is why tonal music can pivot so readily between light and dark. A single voice moving by a half step converts one into the other, and composers lean on that small distance to shade a passage warm or cold without disturbing the harmony's frame.
Major and minor triads
What changes when a C major triad becomes a C minor triad?
Diminished and augmented triads
There are two more triads, and both sound tense, like they need to go somewhere. They are the diminished triad and the augmented triad.
A diminished triad squeezes the notes closer: from C it is C, E-flat, G-flat, and it sounds nervous or spooky. An augmented triad stretches them wider: from C it is C, E, G-sharp, and it sounds strange and unsettled, like it is hanging in the air. Neither sounds finished the way major and minor do; each seems to lean toward another chord.
Play C-E-flat-G-flat, then C-E-G-sharp. Notice how neither feels at rest, unlike the major and minor chords from before.
The diminished and augmented triads alter the fifth: a diminished triad is a minor triad with its fifth lowered a half step, and an augmented triad is a major triad with its fifth raised a half step. A diminished triad stacks two minor thirds, so from C it is C, E-flat, G-flat, and its outer interval is a diminished fifth (six half steps) instead of a perfect one. An augmented triad stacks two major thirds, so from C it is C, E, G-sharp, and its outer interval is an augmented fifth (eight half steps).
Reading them comes down to that altered fifth. Because the top note is squeezed a half step flat or stretched a half step sharp, the perfect fifth that steadies major and minor is gone, which is what makes both chords sound unresolved. They turn up far less often than major and minor, usually as color or as chords that pull toward a more stable one.
Each of these chords stacks two thirds of the same size, and that symmetry strips out the stable frame major and minor depend on. With the outer interval bent to a diminished or augmented fifth, the ear hears a chord that wants to resolve. Composers use that instability deliberately, to push a progression toward a more stable chord.
The diminished triad in particular gets its tension from the tritone inside it, the diminished fifth between its root and top, an interval tonal music treats as unstable; the same tritone gives the dominant seventh its pull toward the tonic. The augmented triad, dividing the octave into equal major thirds, has a floating symmetry that makes its root hard to pin down by ear.
Diminished and augmented triads
How do diminished and augmented triads tend to sound?
Adding a seventh
So far every chord has had three notes. Add one more note on top, stacked another third higher, and you get a four-note chord called a seventh chord. The new note is a seventh above the root, which is where the name comes from.
Take the G major triad, G, B, D, and keep stacking: skip E, land on F, and now you have G, B, D, F, a seventh chord. That extra note adds richness and a little tension, a fuller and more restless sound than the plain triad underneath it.
Start with G-B-D, add an F on top, and play all four. The chord grows richer and leans forward a little with that fourth note.
A seventh chord is a triad with one more third stacked on top, adding a fourth note a seventh above the root. The frame is now root, third, fifth, seventh. Just as the third and fifth came in different sizes, the seventh can be major or minor (or, in the fully diminished seventh chord, diminished), and the combination of triad quality and seventh size names the specific seventh chord.
The seventh is what gives these chords their pull. A triad can sound complete on its own, but adding the seventh introduces a note that leans toward resolution, so in classical music seventh chords tend to drive a progression forward. In jazz and pop, major and minor seventh chords often serve as resting chords. Counting the notes is the same skill as before, extended one more third up the stack.
Adding the seventh continues the same stacking-in-thirds logic one step further, and that single extra note changes a chord's role more than its size suggests. A triad can end a piece on its own. In classical style a seventh chord usually cannot, because the seventh forms a dissonance with the root that the ear expects to resolve downward by step. The chord acquires a direction it did not have before.
This is why seventh chords are engines of harmonic motion. The dissonant seventh wants to fall, the chord wants to change, and a composer uses that built-in tendency to lead from one harmony to the next. Later styles, from Romantic and Impressionist music to jazz, pile still more thirds on top, ninths and elevenths and thirteenths, but the seventh is the first and most common of those additions.
Adding a seventh
How do you turn a triad into a seventh chord?
The common seventh chords
Seventh chords come in a few flavors, and three show up often. The first to learn is the dominant seventh, a bright chord with a strong pull home, written with just a 7, like G7. It is the chord that makes you expect the music to land on its home note next.
The other two soften the sound. A major seventh chord, like C major seventh, sounds warm and dreamy. A minor seventh chord, like D minor seventh, sounds mellow and smooth. You do not need to build them all perfectly yet; the useful idea is that adding a seventh gives you a family of richer chords, each with its own mood.
Find a recording of a jazz or pop tune and listen for those lush, leaning chords. Many of them are seventh chords doing this work.
Three seventh chords come up again and again. The dominant seventh, written with just a 7 as in G7, is a major triad plus a minor seventh, so G7 is G, B, D, F; it is built on the fifth degree of a key and pulls strongly to the tonic. The major seventh is a major triad plus a major seventh, so C major seventh is C, E, G, B, a soft, warm sound. The minor seventh is a minor triad plus a minor seventh, so D minor seventh is D, F, A, C, a mellow sound. Two more have their own names: the half-diminished seventh, a diminished triad plus a minor seventh (B half-diminished seventh is B, D, F, A), and the fully diminished seventh, a diminished triad plus a diminished seventh (B diminished seventh is B, D, F, A-flat).
Tell them apart by two ingredients: the triad quality underneath and the size of the seventh on top. A major triad under a minor seventh gives the restless dominant sound. Keep the major triad but raise the seventh and it turns gentle; start instead from a minor triad with a minor seventh and you get the smooth minor-seventh sound.
What gives the dominant seventh its power is the tritone it holds. Built on the fifth degree, it contains the tritone between the key's fourth and seventh scale degrees, and that restless interval resolves by step, the seventh degree up a half step to the tonic and the fourth degree down to the third of the home chord. It drives the dominant-to-tonic cadence that closes many tonal phrases.
The major and minor sevenths are milder chords. A major seventh softens a major triad by adding a note a half step below the octave, giving the warm sound heard throughout jazz; a minor seventh rounds out a minor triad into something fuller and more relaxed. In each, the triad fixes the basic quality and the seventh adds or eases the tension.
The common seventh chords
Which seventh chord is written with just a 7, as in G7, and pulls toward the home chord?
Ready to play?
You can build a chord now. Name chord qualities on the staff in the game.