On Sleep and Waking

Aristotle. Aristotelis Opera, Volume 3. Bekker, Immanuel, editor. Oxford: Oxford University Press, 1837.

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Cloned and adapted by Humanitext, with ongoing edits.

This work is a scientific and philosophical treatise that investigates the essence and causes of sleep and waking, exploring which parts of the animal body and soul these states belong to. The author begins by demonstrating that it is impossible for any animal to remain perpetually awake or asleep, and establishes that while plants lack these states due to their absence of perception, they are common to all animals that possess sensory capabilities. It is then argued that sleep and waking do not depend on individual senses, but are affections of the "common sensory organ" (koine aisthesis) that governs all perception, with sleep being the temporary suspension of this primary organ's function. Furthermore, the treatise defines sleep as a necessary rest for survival and waking as the purposeful end of activity, locating the physiological source of these phenomena in the heart for red-blooded animals. In the latter half, the physical mechanism of sleep is detailed, explaining how the evaporation of ingested food rises to the head, cools down in the brain, and flows back downward. Finally, the work synthesizes the biological mechanisms of sleeping and waking by linking them to the process of blood separation and heat movement centered around the heart.