The musicologist Jeffrey Kurtzman observed that the five free concertos (or motets) follow a scheme to first increase then decrease the number of singers, from one to three and back to one, but they increase the number of performers from the first to the last, adding more voices at the end of the fourth and having eight instruments play for the last. In prints by other composers, such concertos appear as a group, usually sorted by number of voices, while Monteverdi interspersed them with the psalms.