Hear the motion.
A chord progression is harmony in time. Pick a key, a scale, a pattern. Watch how voices move between chords — which notes hold, which step, which leap. The smoothest connections are the ones the ear already prefers.
Key and scale define which chords are diatonic. Major gives three major, three minor, one diminished. Natural minor inverts the balance. Dorian and Mixolydian shift the colors. Toggle 7ths to add the seventh degree to each chord.
Hit play. The timeline bar tracks position. The keyboard shows each chord as it sounds. Click individual chord cards to hear them in isolation. The degree color tells you the harmonic function — red for tonic, cyan for dominant, green for subdominant.
The arrows between chords show common tones (ct) and voice leading distance (st). More common tones means smoother connection. The voice leading panel below shows exactly how each voice moves — hold, step, or leap. Green is smooth. Orange is wide.
Common tones are notes shared between adjacent chords. I and vi share two of three notes. That is why vi feels like home — it almost is. The more common tones, the smoother the transition.
Voice leading distance is the total semitone movement across all voices. A distance of 2 means one voice moved a whole step while the others held. A distance of 12 means large jumps — dramatic, not smooth.
The best progressions balance smooth voice leading with harmonic motion. Too smooth and nothing moves. Too wide and cohesion breaks. The ear wants change it can follow.
Seventh chords add a fourth voice. More voices means more common tones are possible, and more ways to create smooth connections. Jazz harmony uses sevenths precisely because the voice leading options multiply.
Different scales produce different chord qualities at the same degree. The ii chord is minor in major, but diminished in harmonic minor. Same position in the scale, different tension.