Ioannes Philoponus – Industrious Jack – was a Christian Neoplatonist who worked in Greek Alexandria in the sixth century AD. He was a tireless author. His vast oeuvre, considerable portions of which survive, included commentaries on Aristotle, philosophical treatises, and works of Christian theology and Christian polemic. As a theologian, he was embroiled in the doctrinal disputes of the time, championing the monophysite cause and espousing tritheism. As a philosopher, he was most remarkable – as the title of Richard Sorabji’s splendid book indicates – for his rejection of various parts of the dominant Aristotelian view of the physical universe.
According to Aristotle, the heavens are made of ‘ether’, a fifth element distinct from the four sublunary stuffs – earth, air, fire and water. Philoponus disposed of Aristotle’s arguments for ether. He was thereby able to unify the cosmos – and to maintain inter alia that the sun is actually hot. In Aristotle’s view, the sun is not made of fire, and it warms the world by the friction which its diurnal rotation engenders. Philoponus’s sun is made primarily of fire: it heats because it is hot.
According to Aristotle, the universe has no beginning in time: it has existed for ever and is infinitely old. Philoponus deployed Aristotle’s own notion of infinity against its author. (If, as Aristotle maintained, there can be no actual infinities, then how can the universe have existed for infinitely many ages?) He thereby gave philosophical respectability to the Christian doctrine that the universe was created by God a finite number of years ago.
According to Aristotle, projectiles continue to move because they are pushed along by successive parcels of air. The lancer shoves the air behind the haft. The spear flies forward. The new pocket of air behind it propels it further. Philoponus saw that this was absurd. In its place he substituted an ‘impetus theory’: the lancer imparts a force to his spear; the force remains within the spear and pushes it on until it is eventually exhausted. Philoponus thereby prepared the ground for classical mechanics.
All these points and others are elaborated, with magisterial lucidity and characteristic panache, by Richard Sorabji in the first paper in Philoponus. It is a delicious piece; and any one who doubts, as I have doubted, the interest or importance of Philoponus’s work should read it and be purged. It is also an unusually accessible piece: if you care for the history of philosophy and science, you will find in it pleasure and enlightenment in equal proportion. The other contributors to the volume maintain the superior standard set by the editor and illustrate the several sides of Philoponus’s talents. Henry Chadwick, in an elegant and witty paper, explains the intricacies of Philoponan theology. There is a learned disquisition on impetus theory by Michael Wolff. Lindsay Judson deals subtly with Philoponus’s views on creation. And seven other scholars offer seven other morsels.
Philoponus has not always been popular. For his theological views he was condemned as a heretic, and in 680 was formally anathematised. In philosophy he was little more successful. The pagan Neoplatonist Simplicius, his contemporary and his bitter enemy, attacked him with vigour. He never succeeded to the Chair at Alexandria. He was largely forgotten after his death. And it must be allowed that Jack was a dull boy. The surviving volumes afford few literary delights. The grains of wisdom are hidden in a heap of chaff. And Philoponus was no logician: Simplicius blasted him for his incompetence in technical logic, and a modern reader will find his commentary on Aristotle’s Analytics painfully muddled. Philoponos mataioponos: Jack’s labours lost.
Not altogether. Some of his works, translated into Arabic, stayed to influence Islamic philosophy; and then in 16th-century Italy he enjoyed a renaissance. Bold spirits dared to turn against the authority of Aristotle. Philoponus’s texts were rediscovered and republished – and his Christian opposition to The Philosopher made him something of a hero Galileo read Philoponus, and acknowledged a debt to him. The precise extent of Philoponus’s influence on Galileo is a matter of dispute: but that there was an influence is undeniable. ‘Galileo’s experiment’ is reported by Philoponus, who observes that ‘two unequal weights dropped from a given height strike the ground at almost the same time.’ Perhaps, as Wolff argues, the observation is introduced ad hoc and ‘has no real experimental character’. Nonetheless, it is there in Philoponus’s text.
In recent years Richard Sorabji has been one of the leaders of a second renaissance in Philoponan studies. He has argued that Philoponus’s thoughts about infinity mark ‘a turning-point in the history of philosophy’, and he thinks that Philoponus is a star of the first magnitude. The new book is a sustained effort to explain and justify this assessment. I doubt if it will turn Philoponus into an immediate best-seller. But students of ancient thought can no longer be excused for ignoring the man. We are (once again) indebted to Sorabji for his scholarship and for his analytical skills and for his own exuberant philoponia.