On Dreams   

movement, based on impressions derived from each of the organs of

sense, is preserved in its integrity, renders the dreams healthy,

causes a [clear] image to present itself, and makes the dreamer think,

owing to the effects borne in from the organ of sight, that he

actually sees, and owing to those which come from the organ of

hearing, that he really hears; and so on with those also which proceed

from the other sensory organs. For it is owing to the fact that the

movement which reaches the primary organ of sense comes from them,

that one even when awake believes himself to see, or hear, or

otherwise perceive; just as it is from a belief that the organ of

sight is being stimulated, though in reality not so stimulated, that

we sometimes erroneously declare ourselves to see, or that, from the

fact that touch announces two movements, we think that the one

object is two. For, as a rule, the governing sense affirms the

report of each particular sense, unless another particular sense, more

authoritative, makes a contradictory report. In every case an

appearance presents itself, but what appears does not in every case

seem real, unless when the deciding faculty is inhibited, or does

not move with its proper motion. Moreover, as we said that different

men are subject to illusions, each according to the different

emotion present in him, so it is that the sleeper, owing to sleep, and

to the movements then going on in his sensory organs, as well as to

the other facts of the sensory process, [is liable to illusion], so

that the dream presentation, though but little like it, appears as

some actual given thing. For when one is asleep, in proportion as most

of the blood sinks inwards to its fountain [the heart], the internal

[sensory] movements, some potential, others actual accompany it

inwards. They are so related [in general] that, if anything move the

blood, some one sensory movement will emerge from it, while if this

perishes another will take its place; while to one another also they

are related in the same way as the artificial frogs in water which

severally rise [in fixed succesion] to the surface in the order in