Seventh chords on piano
A seventh chord is a triad plus one more third on top — four notes instead of three. That fourth note is what turns plain harmony into blues, jazz and gospel. The dominant seventh (C7: C–E–G–B♭) is the most common; its built-in tension pulls strongly toward the chord a fifth below.
The family covers five main flavors: dominant 7 (major triad + minor seventh), major 7 (major triad + major seventh, soft and settled), minor 7 (minor triad + minor seventh), half-diminished m7♭5, and the fully diminished dim7, which stacks minor thirds all the way up.
Hear the difference by playing C7 → F, then Cmaj7 on its own. The first demands resolution; the second is happy to sit still. Blues uses dominant sevenths on every chord; jazz standards cycle m7 → 7 → maj7 (the ii–V–I) constantly.
