On Sleep And Sleeplessness   

simple sense any particular sensory faculty whatever, it follows

that in the state called sleep the same affection must extend to all

the special senses; because, if it attaches itself to one of them

but not to another, then an animal while asleep may perceive with

the latter; but this is impossible.

Now, since every sense has something peculiar, and also something

common; peculiar, as, e.g. seeing is to the sense of sight, hearing to

the auditory sense, and so on with the other senses severally; while

all are accompanied by a common power, in virtue whereof a person

perceives that he sees or hears (for, assuredly, it is not by the

special sense of sight that one sees that he sees; and it is not by

mere taste, or sight, or both together that one discerns, and has

the faculty of discerning, that sweet things are different from

white things, but by a faculty connected in common with all the organs

of sense; for there is one sensory function, and the controlling

sensory faculty is one, though differing as a faculty of perception in

relation to each genus of sensibles, e.g. sound or colour); and

since this [common sensory activity] subsists in association chiefly

with the faculty of touch (for this can exist apart from all the other

organs of sense, but none of them can exist apart from it-a subject of

which we have treated in our speculations concerning the Soul); it

is therefore evident that waking and sleeping are an affection of this

[common and controlling organ of sense-perception]. This explains

why they belong to all animals, for touch [with which this common

organ is chiefly connected], alone, [is common] to all [animals].

For if sleeping were caused by the special senses having each and

all undergone some affection, it would be strange that these senses,

for which it is neither necessary nor in a manner possible to

realize their powers simultaneously, should necessarily all go idle

and become motionless simultaneously. For the contrary experience,

viz. that they should not go to rest altogether, would have been

more reasonably anticipated. But, according to the explanation just