  Perhaps some fifteen years after his attack on Aristotle on the eternity of the world (the date is disputed), Philoponus published a commentary on the biblical creation story, On the Creation of the World (De opificio mundi), which is his only theological work extant in Greek.  While discussing the biblical text, Philoponus frequently refers to philosophers like Aristotle, Plato and Ptolemy as well as to Basil the Great, whose own treatise on the creation served him as inspiration. The De opificio mundi has received some attention from historians of science, because Philoponus suggests at one point (I 12) that the movement of the heavens could be explained by a ‘motive force’ impressed on the celestial bodies by God at the time of creation. As we have seen (2.2 above), Philoponus discussed impetus theory for the first time in the context of trying to understand the physics of forced motion (Why does an arrow or stone continue to move after losing contact with its motive cause?). Now he applies the same theory to the regular and natural motions of the universe at large. Significantly, Philoponus assimilates the supposed rotational impetus implanted by God into the celestial bodies to the rectilinear movements of the elements as well as to the self-movements of animals. The interesting upshot is that all these different types of natural and non-natural motions are understood in essentially the same way as impetus- induced movements. In virtue of this bold suggestion Philoponus is often credited with having envisaged, for the first time, a unified theory of dynamics, since he strove to give the same kind of explanation for phenomena that Aristotle and others had to explain by appeals to different kinetic principles such as nature, coercion, or soul, depending upon context.