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Chords and voice leading
A major chord is already present inside a single note: harmonics 4, 5 and 6 of a low C are C, E and G. When one chord follows another, musicians usually prefer that each voice moves as little as possible to its next note. This is called voice leading. In 1739 Leonhard Euler drew a map of notes, later called the Tonnetz, where chords that share two notes sit next to each other. On this map, smooth progressions are short walks.