 "Structures I" was the last and most successful of Boulez's works to use the technique of integral serialism , wherein many parameters of a piece's construction are governed by serial principles, rather than only pitch.Boulez devised scales of twelve dynamic levels (though in a later revision of the score these reduced to ten—), twelve durations, and—from the outset—ten modes of attack , each to be used in a manner analogous to a twelve-tone row.The composer explains his purpose in this work