In 1952, after the completion of The Rake's Progress, Stravinsky embarked on a remarkable voyage of compositional discovery. His late works differ from his earlier ones in striking and profound ways. During the final two decades of his life, every major work was almost shockingly new, right down to original, and ever-changing, principles of structural formation. The works in this period describe a succession of compositional firsts, including his first works to use a series (Cantata , Septet [ 1953], Three Songs from William Shakespeare ); his first fully serial work (In Memoriam Dylan Thomas ); his first work to use a twelve-tone series (Agon [1954-57]); his first work to include a complete twelve-tone movement ("Surge, aquilo," from Canticum Sacrum ); his first completely twelve-tone work (Threni ); his first work to make use of twelve-tone arrays based on hexachordal rotation (Movements ); his first work to use the verticals of his rotational arrays (A Sermon, A Narrative, and A Prayer [1961 ]); his first work to rotate the series as a whole (Variations ); his first work to rotate the tetrachords of the series (Introitus ); and his first work to use two different series in conjunctio (Requiem Canticles —his last major work).
The pattern of innovation is remarkable, persistent, and unprecedented. I can think of no other major composer, at a comparably advanced age and pinnacle of recognition and success, who so thoroughly altered his compositional approach, or whose late works differ so greatly from his earlier ones. While there is some truth in the cliche that Stravinsky always sounds like Stravinsky, nonetheless the late works differ radically from the earlier ones at every level, from their deep modes of musical formation to the rhythmic and intervallic details of the musical surface. Furthermore, Stravinsky's late works are not only radically different from the earlier ones, but are highly individuated from each other as well. There is no major work in this period in Stravinsky did not try something new.
Straus, Joseph N., "Stravinsky's Serial "Mistakes"" (1999). CUNY Academic Works.