Anastasius of Sinai was one of the most creative theologians in the period when Late Antiquity was transforming to the Middle Ages. His passionate rhetoric targeted the Christological unorthodoxies of his time, primarily Monenergism and Monothelitism. In his polemics against these doctrines, Anastasius creatively elaborated on the arguments of his predecessors. He developed a complex, and sometimes surprising, taxonomy of Christ’s activities and volitions. This taxonomy included mixed human-divine, pure divine, and pure human energeiai and wills, which, to Anastasius, proved duality of Jesus Christ.