  The question of the immortality of the soul is a potential point of conflict between Orthodox Christian doctrine and Byzantine natural philosophy. Byzantine natural philosophy, like its late antique predecessor, was largely based on the works of Aristotle. In Book 2 of the De anima, Aristotle defines the soul as “the first actuality of a natural body which potentially has life.” He himself draws the conclusion that the soul must be inseparable from the body. It seems clear, too, that on this view the soul cannot survive the moment of the body’s death. Still, Aristotle leaves open the possibility that there may be some part of the soul that is not the actuality of a body, and therefore may be separable. As he explains in Book 3 of the De anima, the mental faculty by which we think and form beliefs, nous, variously translated as “mind” or “intellect”, in fact lacks a bodily organ. In one of the most intriguing and hotly debated passages of ancient philosophy, De anima Book 3, chapter 5, Aristotle introduces the notion of a kind of intellect that he describes as productive and active, and this kind of intellect, according to him, is not only separable from the body but is “alone immortal and eternal.” The question, then, is whether the eternal life of this productive and active intellect is enough to ensure survival after death for the individual human soul.