Aristotle on sleep and dreams 175
That is explicitly and emphatically the context of natural science: the the-
oretical study ofnatureas Aristotle conceives it. They belong to a series of
treatises which are usually calledParva naturalia. Although this title does
not originate from Aristotle but from the Middle Ages, it rightly indicates
that psychology means for Aristotle psycho-physiology, an analysis both of
the formal (‘mental’) and of the material (‘physical’) aspects of what it
means for a natural entity to be a living being.^17 At the beginning of this
series of treatises (which Aristotle seems to have conceived as a continuing
discussion of connected topics), Aristotle says that he will be concerned
with the most important ‘activities and experiences’ of living beings (man,
animals, plants), in particular with those that are ‘common to the soul and
the body’: sense-perception, memory and recollection, sleep and waking,
youth and old age, growth and decay, breathing, life and death, health and
disease. These are, Aristotle says, the most important functions living be-
ings can realise or experiencequaliving beings, and it is for the purpose
of these functions that the bodily structures such as described inHistory of
AnimalsandParts of Animals(and in the lost workOn Plants) exist. The
Parva naturaliaare closely linked to Aristotle’s workOn the Soul, and the
psycho-physiological explanation of dreams which Aristotle expounds in
On Dreams(and which, in the enumeration listed above, is subordinated
to and included in the discussion of sleeping and waking) heavily draws
upon Aristotle’s general theory of the soul, especially his views on sense-
perception, ‘imagination’ (phantasia), and on the so-called ‘central sense
faculty’ (kurion aisth ̄et ̄erion). This context of the study of nature should
make clear from the outset that the interest taken by Aristotle in dreams is
neither epistemological nor practical, hermeneutic or therapeutic – as it is,
for example, in the Hippocratic workOn Regimenquoted above, of which
Aristotle was aware.
Against this background, the questions Aristotle is pursuing in the three
works in question make perfect sense. Thus in the preface toOn Sleep and
Waking( 453 b 11 – 24 ), which in a way serves as an introduction to all three of
the treatises, he says that he is going to consider whether sleeping and waking
are ‘peculiar to the soul’ or ‘common to soul and body’, and, if common to
both, what parts of soul and body are involved; whether sleep occurs in all
living beings or only in some; and through what cause (aitia) it occurs.^18
Considering this psycho-physiological context, one would expect Aris-
totle to pay some attention to the question of the possibility of cognition
(^17) On the structure and underlying rationale of the series of treatises assembled under the heading
Parva naturaliasee van der Eijk ( 1994 ) 68 – 72 ; see also Morel ( 2000 ) 10 – 24 and ( 2002 b).
(^18) For a discussion of this ‘Preface’ see van der Eijk ( 1994 ) 68 – 72.