'The universe is, as it were, one machine, wherein the celestial spheres are analogous to the interlocking wheels and the particular beings are like the things moved by the wheels' and all events are determined by an inescapable necessity. To speak of free choice or self determination is only an illusion we human beings cherish. Thus writes Theodore the engineer to his old friend Proclus. Proclus' reply is one of the most remarkable discussions...