Starting in the late 1940s his music shows an increasing development of a personal harmonic and rhythmic language characterized by elaborate rhythmic layering and metric modulation. While Carter's chromaticism and tonal vocabulary parallels serial composers of the period, Carter did not use serial techniques. Carter said, "I certainly have never used a twelve-tone row as the basis of a composition, in the way described in Schoenberg’s "Style and Idea", nor are my compositions a constant rotation of various permutations of twelve-tone rows". Rather, he independently developed and catalogued all possible collections of pitches (i.e., all possible three-note chords, five-note chords, etc.), compiling what he called his "Harmony Book." (An edited version of the book was published in 2002 by Carl Fischer Music.) Musical theorists like Allen Forte later systematized these data into musical set theory. A series of Carter's works in the 1960s and 1970s generates its tonal material by using all possible chords of a particular number of pitches.