After 1940, Hauer wrote exclusively "Zwölftonspiele", designated sometimes by number, sometimes by date. He wrote about one thousand such pieces, most of which are lost. These pieces were all built on an ordered twelve-tone row, with the actual order often determined by chance. These pieces were not so much concert pieces as much as systematic and controlled meditations on the twelve tones—more a means than an end. Hauer believed that the twelve tempered tones provided access to the realm of the spiritual; meditating on the twelve tones was thus a prayerful act and not a public display of personal emotion or expression. In many ways Hauer's use of chance elements, and especially his deep interest in the "I Ching", are parallel to those of American composer John Cage.