Cosmology

The doctrine that the world was eternal was undoubtedly the single doctrine of Aristotelian natural philosophy that Byzantine writers found hardest to swallow. In contrast to some of the late antique and medieval commentators (including Thomas Aquinas), they tended to resolve the tension between this doctrine and (Platonic or Christian) creationism not by recourse to a theory of creation which allowed for the world’s being eternal, but by rejection of the Aristotelian doctrine. The example was set by Philoponus, who attempted to prove through philosophical argument, in his Contra Proclum (529), Contra Aristotelem, and De contingentia mundi, that it is both possible and necessary for the world to have had a beginning, before he proceeded to show by scriptural exegesis that the biblical account of creation does not contradict the findings of natural philosophy (De opificio mundi, probably 550s). Thus he maintained, against the literal interpretation of Genesis advanced by Kosmas Indikopleustes and other followers of the Antiochene school of exegesis, that the cosmos is a system of nested spheres, the outermost of which, being responsible for the diurnal movement from east to west, encompasses the fixed-star sphere, seven lower spheres each carrying the epicycle ofa planet, and, at the center, the small immovable spherical earth. Against the Aristotelian-Ptolemaic world-view, however, he argued that the celestial realm is not composed of a fifth ungenerable and imperishable kind of body, but of different mixtures of the four elements (mostly water and air in crystalline form); and that the movement of the heavenly spheres is not due to their eternal nature, but to the motive force impressed in them by God. He also repudiated a view which he seems to have still held in his works against Proclus and Aristotle on the eternity of the world, namely, that the heavenly spheres and bodies have souls.

Much the same basic cosmology is defended with similar arguments by numerous later authors. Symeon Seth (CRN30) and Nikephoros Blemmydes (EP24) both assume that the doctrine that the world has had a beginning can be scientifically proved, and they both draw their arguments from Philoponus; Michael Psellos (OD 157) more cautiously refers only to Scripture.

Aristotelian-Ptolemaic celestial mechanics is more or less universally accepted, but the five-elements-theory is discarded as groundless. Choumnos, for instance, points out that Aristotle’s attempt to deduce his theory from the fact that the heavens have a circular movement fails, inasmuch as he has only secured the premise that all simple bodies have simple movements, not that all simple movements belong to simple bodies, which is what his argument requires. Most authors either agreed with Philoponus in De opificio mundi or followed the Platonic view that the heavens consist of an elemental mixture dominated by fire, but Choumnos accepted Plotinus’ view that they consist of fire alone.