Aristotle on sleep and dreams 183
these weaker movements, which escaped our attention in the waking state,
get, so to speak, a second chance to ‘present themselves’ to the perceiving
subject. They are ‘reactivated’ and ‘come to the surface’ ( 461 a 3 , 7 ). This is
an operation of the faculty of ‘imagination’. The physiological picture to
be drawn for this process is not completely clear, but seems to be roughly as
follows. Aristotle thinks that apart from the peripheral sense-organs (eyes,
ears, nose, etc.) there is also a central, co-ordinating sense-organ located in
the heart (the so-called ‘principle of perception’, 461 a 6 , 31 ; 461 b 4 ). His
view seems to be that, normally speaking, a sensitive impulse is transmitted
from the peripheral sense-organs to the heart, where it is received, recorded
and noticed, and co-ordinated with movements from other senses ( 461 a 31 ).
The transmitting agency is probably the blood (although this is not quite
clear from the text).^26 In the waking state, the weaker sense-movements,
which have arrived at the peripheral sense-organs during the waking state,
are prevented from reaching the heart because of the competition with
stronger movements; it is only in sleep, when the blood withdraws from
the outer parts of the body to the inner parts, that they penetrate to the
heart. The ‘perception’ or ‘noticing’ of these movements is dreaming in the
strict sense. Thus dreams originate from weak sense-movements, which
have entered the sense-organs in the waking state, but which were not
noticed by the perceiving subject because of their weakness in comparison
with stronger movements.
By explaining the occurrence of dreams in this way, Aristotle manages
to account for the fact that dreams often display many similarities with
what the dreamer has experienced in the waking state (because they consist
of movements received during the waking state), but that these elements
often appear in a distorted, completely ‘unrealistic’ configuration due to
the physiological conditions that influence the transmission to the heart.
In order to substantiate this explanation, Aristotle has to presuppose, first,
that the sense-organs actually receive very slight movements and, second,
that these small movements are being ‘preserved’ (soizesthai ̄ , 461 a 25 )inthe
sense-organs from the moment of their arrival (in the waking state) to
the moment of their transport to the heart and subsequent appearance in
sleep.
When we look at our list of empirical ‘data’, we can see that numbers
3 – 9 are used by Aristotle in order to illustrate the mechanism of ‘linger-
ing’ or ‘persisting’ sense-movements after the actual perception has disap-
peared; numbers 8 – 9 point to the receptivity of the sense-organs to small
(^26) See 461 a 25 and b 11 , 27. See van der Eijk ( 1994 ) 81 – 7 and, with reservations, Johansen ( 1998 ).