Aristo (there were two philosophers by this name, one a Stoic, the
other an Aristotelian) attributes to the soul a perceptive faculty,
which he divides into two parts. According to him, the first, called
sensibility, the principle and origin of sensations, is usually kept
active by some one of the sense-organs. The other, which subsists
by itself, and without organs, does not bear any special name in
beings devoid of reason, in whom reason does not manifest, or at
least manifests only in a feeble or obscure manner; however, it is
called intelligence in beings endowed with reason, among whom alone
it manifests clearly. Aristo holds that sensibility acts only with
the help of the sense-organs, and that intelligence does not need
them to enter into activity. Why then does he subordinate both of
these to a single genus, called the perceptive faculty? Both doubtless
perceive, but the one perceives the sense-form of beings, while the
other perceives their essence. Indeed, sensibility does not perceive
the essence, but the sense-form, and the figure; it is intelligence
that perceives whether the object be a man or a horse. There are,
therefore, two kinds of perception that are very different from each
other; sense-perception receives an impression, and applies itself to
an exterior object; on the contrary, intellectual perception does not
receive any impression.
There have been philosophers who separated these two parts; they called
intelligence or discursive reason the understanding which is exercised
without imagination and sensation; and opinion, the understanding
which is exercised with imagination and sensation. Others, on the
contrary, considered rational "being," or nature, a simple essence,
and attributed to it operations whose nature is entirely different.
Now it is unreasonable to refer to the same essence faculties which
differ completely in nature; for thought and sensation could not depend
on the same essential principle; and if we were to call the operation
of intelligence a perception, we would only be juggling with words.
We must, therefore, establish a perfectly clear distinction between
these two entities, intelligence and sensibility. On the one hand,
intelligence possesses a quite peculiar nature, as is also the case
with discursive reason, which is next below it. The function of the
former is intuitive thought, while that of the latter is discursive
thought. On the other hand, sensibility differs entirely from
intelligence, acting with or without the help of organs; in the former
case, it is called sensation; in the latter, imagination. Nevertheless,
sensation and imagination belong to the same genus. In understanding,
intuitive intelligence is superior to opinion, which applies to
sensation or imagination; this latter kind of thought, whether called
discursive thought, or anything else (such as opinion), is superior to
sensation and imagination, but inferior to intuitive thought.