182 Aristotle and his school
refers explicitly in 463 a 4 – 5 ), and perhaps also from literary descriptions
of dreams such as were found in Homer and the epic tradition. However,
since this tradition has only been preserved in fragments, it is difficult to
assess the extent of his dependence on earlier sources.
Yet when looking more closely at the way in which these empirical
‘data’ are used in Aristotle’s argument inOn Dreams, it becomes clear that
the treatise goes far beyond the level of empirical fact-finding. Aristotle
does not present his theory as being built up, so to speak, inductively on
the basis of a number of observations; on the contrary, the three research
questions mentioned above ((i), (ii) and (iii)) are treated in a systematical
and deductive way, and empirical ‘data’ are mentioned in the course of this
theoretical argument – often in the form of examples or analogies – in
order to support or clarify opinions and presuppositions which Aristotle
already seems to take for granted. And although Aristotle’s style of reasoning
seems very cautious and essayistic – the first chapter, for example, is highly
aporetic^25 – it is, in fact, rather dogmatic. The general impression one gets is
that empirical evidence is primarily mentioned when it suits the argument –
and if not, it is either ignored or explained away in a questionable manner.
Thus at the end ofOn Dreams, it turns out that the three questions raised
at the beginning are to be answered as follows:
(i) Dreams belong to the sensitive part of the soulquaimaginative part
( 459 a 21 ); dreaming is not an operation of sense-perception but of ‘imag-
ination’, which is defined by Aristotle as ‘the movement which occurs as
a result of actual perception’ ( 459 a 17 – 18 ). This definition, together with
Aristotle’s use of the wordsphantasia,phantasma, andphainesthai,isin
broad agreement with his general theory of ‘imagination’ inOn the Soul,
to which he explicitly refers ( 459 a 15 ). In the course of the long argument
which leads to this conclusion, only claims ( 1 ) and ( 2 ) play a part; for the
rest, the argument is purely theoretical and logical.
(ii) How do dreams come into being? Aristotle assumes the following
mechanism: During the waking state, the sense-organs are stimulated by
a great quantity of sense-movements (stimuli brought about by sensible
objects); but not all of these movements are equally strong. The stronger
movements overrule the weaker, so that the weaker are ‘not noticed’ by the
perceiving subject ( 460 b 28 – 461 a 8 ). Aristotle assumes, however, that the
remnants of these weaker movements remain present in the sense-organs
in the form of traces. When in sleep the sense-organs have stopped being
active – and as a result of this cannot receive new stimuli – the remnants of
(^25) For an analysis see van der Eijk ( 1994 ) 36 – 8.