198 Aristotle and his school
small movements escape our notice because they are overruled by more
powerful ones, whereas in sleep, as a result of the lack of input of strong
actual movements, the small ones get a chance to present themselves. This
principle is demonstrated by means of a number of examples derived from
common experience (no. 2 on the list above). The second principle is that
the origins of all things (including diseases) are small and therefore belong
to the category of small movements. The two principles are combined in
the form of a syllogism at the end of the paragraph.
These points are most relevant for an assessment of what Aristotle is do-
ing in the passage under discussion. It has, of course, long been recognised
by commentators that the sentence 463 a 4 – 5 may very well be a reference
to the Hippocratic treatiseOn Regimen, the fourth book of which deals
with dreams and which I quoted at the beginning of this chapter. Although
the Hippocratic Corpus contains several examples of the use of dreams as
prognostic or diagnostic clues,^49 we nowhere find such an explicit theoret-
ical foundation of this as in this book. It is chronologically possible and
plausible that Aristotle knew this treatise, because other places in theParva
naturaliashow a close similarity of doctrine toOn Regimen.^50 That he is
referring to it here becomes more likely when we consider that the writer
ofOn Regimencertainly meets Aristotle’s requirements for being acharieis
iatros. Moreover, the author’s approach must have appealed to Aristotle for
the very fact that the interest of dreams is that they reveal thecausesof
diseases.
However, these similarities should not conceal the fundamental differ-
ence of approach between the medical writer and Aristotle. This difference
not only manifests itself in that Aristotle, as a natural scientist, is only inter-
ested in the causal relationship between the dream and the event, whereas
On Regimenis primarily a text about regimen (both from a preventive and
from a therapeutic point of view), which explains the great amount of de-
tailed attention paid to the interpretation of the contents of dreams and
to prescriptions about preventive dietetic measures. The most important
difference lies in the psycho-physiological explanation of the significance
of dreams given by the two authors. The author ofOn Regimenappeals to
a rather ‘dualistic’ conception of the relation between soul and body, of the
type referred to earlier on in this chapter:
(^49) See the instances listed in van der Eijk ( 1994 ) 279. The most explicit statement apart fromOn Regimen
86 is ch. 45 of the treatiseOn Sevens, but this is considered by most scholars to be post-Aristotelian.
(^50) On this see W. D. Ross ( 1955 ) 56 – 7 , who points out that Aristotle’s ‘comparison of the heart-lung
system to a double bellows [inDe respiratione 480 a 20 – 3 ] is clearly borrowed fromVict.’; see also
Byl ( 1980 ) 321 n. 32 and 325 , and Lef`evre ( 1972 ) 203 – 14.