Aristotle on the causes of sleep

Abstract

For more than half a century, scholars have been debating how many causes of sleep were discussed by Aristotle in the treatise On Sleep and Wakefulness (De Somno et Vigilia). Some commentators believed that Aristotle did not offer a formal explanation of sleep, others argued that sleep has no material cause, still others do not find either effective or final cause of it. The controversy is provoked by the very course of reasoning in the treatise, in the middle of which Aristotle promises to investigate all four causes of the sleep, but further on doesn’t say a word about either its form or matter. As for the efficient cause of sleep, it also remains highly controversial. Scholars disagree as to what physiological change in the animal body makes the central organ of perception incapable of perceiving – whether it is due to the heart being cooled, or warmed, or compressed by blood in a mixed condition. In the present paper I intend to propose a new interpretation of Aristotle’s theory of sleep in the light of recent discussions about the causes of sleep in Parva naturalia. To achieve this goal, I examine Aristotle’s explanatory method in the De anima, focusing on the question of whether sleep along with other living being’s activities involving soul and body (λόγοι ἔνυλοι), can be explained in terms of formal, final, material and effective causes. Particular attention is paid to the role of material and effective causes in the physiological explanation of sleep. While reconstructing Aristotle’s explanatory method I clarify the structure of the argument in the De Somno and resolve some of the problems concerning the unity of this work.