Voice leading is the way that musical parts (voices) set up and achieve melodic, harmonic and formal goals using pitch and rhythm. Often, a variety of parameters work together to produce different weights of arrival. Such parameters may include "the interaction between chords and lines within harmonic progressions [...], the role of outer-voices counterpoint, the types of melodic motion, the retention of common tones, [and] the treatment of dissonance.” Monophonic lines also exhibit voice leading.