Pärt's works are generally divided into two periods. He composed his early works using a range of neo-classical styles influenced by Shostakovich, Prokofiev, and Bartók. He then began to compose using Schoenberg's twelve-tone technique and serialism. This, however, not only earned the ire of the Soviet establishment but also proved to be a creative dead-end. When early works were banned by Soviet censors, Pärt entered the first of several periods of contemplative silence, during which he studied choral music from the 14th to 16th centuries. In this context, Pärt's biographer, Paul Hillier, observed that "he had reached a position of complete despair in which the composition of music appeared to be the most futile of gestures, and he lacked the musical faith and willpower to write even a single note."