Carl Dahlhaus (1990) distinguishes between "coordinate" and "subordinate harmony". "Subordinate harmony" is the hierarchical tonality or tonal harmony well known today. "Coordinate harmony" is the older Medieval and Renaissance "tonalité ancienne", "The term is meant to signify that sonorities are linked one after the other without giving rise to the impression of a goal-directed development. A first chord forms a 'progression' with a second chord, and a second with a third. But the former chord progression is independent of the later one and vice versa." Coordinate harmony follows direct (adjacent) relationships rather than indirect as in subordinate. Interval cycles create symmetrical harmonies, which have been extensively used by the composers Alban Berg, George Perle, Arnold Schoenberg, Béla Bartók, and Edgard Varèse's "Density 21.5".