Matter of sleep. Byzantine commentators of the 12th - 15th centuries on the material cause of sleep in Aristotle’s treatise on sleep and waking (de somno et vigilia)

The paper gives a general description of the surviving Byzantine commentaries on Aristotle’s small psychological treatises traditionally known as Parva naturalia and describes the most notable manuscripts and editions of commentaries compiled by Michael of Ephesus, George Pachymeres, Theodore Metochites, Sophonias and Gennady Scholarios. The paper clarifies the relationships of these texts to each other, discusses possible reasons of the renewal of interest in biological and physiological aspects of Aristotle’s philosophy among Byzantine scholars of the 12th - 15th centuries, and explains why the late antique commentary tradition paid little attention to particular issues of Aristotle’s philosophy of nature. We establish distinctive features of Byzantine exegesis by examining how Byzantine commentators dealt with some controversial questions of Aristotle’s treatise On sleep and waking , in particular how they explain the fact that after promising to consider the formal, final, effective and material causes of sleep, Aristotle explores only three of them and leaves the material one without attention. We demonstrate that Byzantine commentators were convinced of the existence of the material cause of sleep and identified the latter with the hot evaporation that necessarily arises from food in digestion. However, the analysis of this interpretation shows that it was based on a misunderstanding of the basic concepts of Aristotelian philosophy, since Byzantine commentators aimed more at preserving Aristotle's texts than at better understanding the general order of his philosophy.