Seventh Chords

A triad has three notes stacked in thirds. A seventh chord takes that triad and adds one more third on top, giving a fourth note that sits a seventh above the root. That extra note colours the whole chord, turning plain, stable harmony into something richer, moodier, and full of forward motion.

Building a seventh chord

Start from a root, stack a third, another third, and a third again. On C that gives C E G (the triad) plus a fourth note a seventh above C. Which exact notes you use for the top two pitches decides the type of seventh chord, and each type has its own character.

The five common types

Almost all seventh chords you meet are one of these five. Read them as a triad plus a seventh:

• Major 7th (Cmaj7 = C E G B): a major triad plus a major 7th. Lush and warm.
• Dominant 7th (C7 = C E G B♭): a major triad plus a minor 7th. Restless and wanting to resolve.
• Minor 7th (Cm7 = C E♭ G B♭): a minor triad plus a minor 7th. Smooth and mellow.
• Half-diminished 7th (Cm7♭5 = C E♭ G♭ B♭): a diminished triad plus a minor 7th.
• Diminished 7th (Cdim7 = C E♭ G♭ B𝄫): a diminished triad plus a diminished 7th. Fully symmetrical and very tense.

Note the diminished 7th's top note: B𝄫 is written as a double-flat because it is spelled a diminished seventh above C, even though on the keyboard it sounds the same as A. The chord divides the octave into four equal minor thirds, which is why it feels so unsettled.

Why the dominant 7th matters

The dominant 7th is the engine of tonal music. It is built on the fifth degree of a key, so in C major the dominant 7th is G7 (G B D F). Inside it hide two notes a tritone apart, B and F, and that interval is deeply unstable. The ear hears it as tension that must release: B pulls up to C and F pulls down to E, landing you on a C major chord.

This motion from the dominant 7th to the tonic, written V7 to I, is the strongest cadence in Western music. It is how countless pieces say "we have arrived home."

Try it yourself

Hearing the difference is the fastest way to learn it. Build each chord below, starting from C, and listen to how a single altered note reshapes the mood. Toggle the top note between B and B♭ to feel the leap from major 7th to dominant 7th, then flatten the third and fifth to explore the minor and diminished colours.

Once these five shapes are in your ears and under your fingers, most of the harmony in jazz, pop, and classical music will start to sound familiar. Seventh chords are where colour and motion truly begin.