His principal teacher was Messiaen, and he also studied counterpoint privately with Andrée Vaurabourg. According to Boulez, composition was a form of aesthetic research and should be pursued logically. He viewed personal stylistic development as having no importance and deemed atonality as necessary. He adopted 12-tone serialism after being exposed to it by René Leibowitz, a student of Schoenberg. In Structures for two pianos (1952), Boulez utilized a serial control of rhythm, dynamics, and tone. These works brought him initial public recognition, but it was his Le Marteau Sans Maître (1954) that was to become a landmark of 20th century music. Scored for small ensemble, it is rhythmically monotonous with sudden tempo changes and large sections of improvisatory melodies. The success of these pieces led to an invitation to teach at Darmstadt, as a professor of composition. It was here that he gave a series of lectures that was to become the book Musikdenken Heute, an outline of his ideas concerning total serialization. At this time Boulez was expanding his serial techniques to include open form, or "organized delirium." He also developed techniques that allowed performer and conductor to make many more creative choices in form and tonal duration. Boulez was also an active conductor, his performances marked by analytical clarity. He served as head conductor for the BBC Symphony in London and the New York Philharmonic. ~ Lynn Vought