Harmony

1. The arrangement of parts within a structure or system in pleasing relation to each other.

2. The degree of efficiency with which a particular system achieves its purpose. A norm of harmony is distinguished from a norm of equilibrium which refers to the degree of interrelatedness between an equilibrium system as a whole and whatever are taken to be its parts.

3. Combination into a consistent whole.

4. The science of the structure, relation, and progression of chords in homophonic composition.