Quadrivium: The Four Classical Liberal Arts of Number, Geometry, Music, & CosmologyThe quadrivium the classical curriculum comprises the four liberal arts of number, geometry, music, and cosmology. It was studied from antiquity to the Renaissance as a way of glimpsing the nature of reality. Geometry is number in space; music is number in time; and cosmology expresses number in space and time. Number, music, and geometry are metaphysical truths: life across the universe investigates them; they foreshadow the physical sciences.