The Order of Harmony
2. Whenever two or more impressions or ideas have something in common that is appreciable, they are in harmony, in the measure of what they have in common. The harmony increases as the common element increases; or the common elements. It diminishes in the measure of every difference or contrast. By the Order of Harmony I mean some recurrence or repetition, some correspondence or likeness. The likeness may be in sounds or in sights, in muscular or other sense-impressions. It may lie in sensations, in perceptions, in ideas, in systems of thought.