The shortest path.
Voice leading is how individual notes move from one chord to the next. Good voice leading moves each voice by the smallest interval possible. The smoothest connection between two harmonies is usually the most beautiful one.
Bach spent his life perfecting voice leading. Each voice in a chorale is a melody. Good voice leading means every melody sounds natural on its own, even though they combine into complex harmony.
Common tones are the glue between chords. When C major moves to A minor, E stays put while C descends to A and G rises to A. Two of three voices barely move. That continuity is why vi feels so close to I.
The tritone resolution is why V-I works. In G7 to C, the B rises a semitone to C while the F falls a semitone to E. Two notes each moving one step in opposite directions. Maximum tension releasing to maximum stability.
Parallel fifths sound hollow because they fuse two voices into one. Renaissance composers banned them not from arbitrary rules but because the ear stops hearing independent melodies. Voice independence is the goal.
Drop-2 voicings spread voices across a wider range, giving each note room to breathe. Jazz guitarists use them because the guitar cannot play close voicings easily. The constraint produced a distinctive sound.
Notes shared between two chords. These voices hold still while others move. More common tones means a smoother, more connected transition. I to vi shares two. I to V shares one. I to bII shares zero.
Stepwise motion (1-2 semitones) sounds natural. Leaps (3+) are dramatic. Contrary motion (voices moving in opposite directions) creates independence. Parallel motion blends voices. Oblique motion holds one voice still.
The sum of all voice movements in semitones. Lower is smoother. Under 4 is very smooth. 5-8 is moderate. Over 8 is a large harmonic shift — sometimes dramatic, sometimes jarring, depending on context.