On Sleep And Sleeplessness
either some external movement or else some movement in his own
consciousness. If waking, then, consists in nothing else than the
exercise of sense-perception, the inference is clear, that the
organ, in virtue of which animals perceive, is that by which they
wake, when they are awake, or sleep, when they are awake, or sleep,
when they are asleep.
But since the exercise of sense-perception does not belong to soul
or body exclusively, then (since the subject of actuality is in
every case identical with that of potentiality, and what is called
sense-perception, as actuality, is a movement of the soul through
the body) it is clear that its affection is not an affection of soul
exclusively, and that a soulless body has not the potentiality of
perception. [Thus sleep and waking are not attributes of pure
intelligence, on the one hand, or of inanimate bodies, on the other.]
Now, whereas we have already elsewhere distinguished what are called
the parts of the soul, and whereas the nutrient is, in all living
bodies, capable of existing without the other parts, while none of the
others can exist without the nutrient; it is clear that sleep and
waking are not affections of such living things as partake only of
growth and decay, e.g. not of plants, because these have not the
faculty of sense-perception, whether or not this be capable of
separate existence; in its potentiality, indeed, and in its
relationships, it is separable.
Likewise it is clear that [of those which either sleep or wake]
there is no animal which is always awake or always asleep, but that
both these affections belong [alternately] to the same animals. For if
there be an animal not endued with sense-perception, it is
impossible that this should either sleep or wake; since both these are
affections of the activity of the primary faculty of sense-perception.
But it is equally impossible also that either of these two
affections should perpetually attach itself to the same animal, e.g.
that some species of animal should be always asleep or always awake,