CHAPTER V.
Note 1, p. 84. In our treatises upon action and im-
pression, &c.] Some commentators have, in the treatises
here alluded to, seen only a reference to other disquisitions,
as those upon "'reproduction and destruction,' or decay,"
περὶ γενέσεως καὶ φθοράς; but as the passages which are
cited do not meet the whole question, it has been suggested
by Trendelenberg that the allusion may be to some other
work which has not come down to us.
Note 2, p. 84. It is difficult to understand, &c.] In
another chapter of this treatise, Aristotle has alluded to
the power possessed by the senses of recalling former
impressions; of realizing images at will, that is, without
external objects. But the question here is to learn why
the senses, which were supposed to be derived from the
elements, from which or the accidents of which sensation
itself was derived, are not in constant activity. The
answer is, that the normal state, so to say, of the sensi-
bility is potentiality, and that it is insusceptible, there-
fore, of perception, without impression by something
from without to call it into action; just as the combustible
material requires, in order to burn, the agency of fire.
But the comparison contains a converse proposition, as
while the material is required for the sensibility, it is fire,
