Definition of harmony and succession of 2 consecutive chords, regarding to the voice leading by contrary, parallel, direct or oblique motion. Any chord may be presented in different positions, for example in a closed position, open position, in thirds, fourths, clusters or reversed. The chord is a vertical conception of music where the sounds are stacked vertically and played at the same time. Harmony is the concatenation of two or more chords following each other. We will pay attention to the horizontal voice leading. Indeed, each note of a chord has a horizontal movement toward a melodic note of the next chord. A voice leading responds to special rules, such as: - Avoid a simultaneous upward and downward movement of the four voices, because the resulting sound will be boring. Conversely, in the second example: the first voice remains in place, the second voice rises, also rise the third voice, and the fourth voice is going down. There is therefore a combination of ascending, descending and horizontal melodic movements. This voice leading remains more interresting at the hearing.