Whether Intellectual Knowledge Is Derived from Sensible Things?
Objection 1: It would seem that intellectual knowledge is not derived
from sensible things. For Augustine says (QQ. 83, qu. 9) that "we
cannot expect to learn the fulness of truth from the senses of the
body." This he proves in two ways. First, because "whatever the
bodily senses reach, is continually being changed; and what is never
the same cannot be perceived." Secondly, because, "whatever we
perceive by the body, even when not present to the senses, may be
present to the imagination, as when we are asleep or angry: yet we
cannot discern by the senses, whether what we perceive be the
sensible object or the deceptive image thereof. Now nothing can be
perceived which cannot be distinguished from its counterfeit." And so
he concludes that we cannot expect to learn the truth from the
senses. But intellectual knowledge apprehends the truth. Therefore
intellectual knowledge cannot be conveyed by the senses.
Obj. 2: Further, Augustine says (Gen. ad lit. xii, 16): "We must not
think that the body can make any impression on the spirit, as though
the spirit were to supply the place of matter in regard to the body's
action; for that which acts is in every way more excellent than that
which it acts on." Whence he concludes that "the body does not cause
its image in the spirit, but the spirit causes it in itself."
Therefore intellectual knowledge is not derived from sensible things.
Obj. 3: Further, an effect does not surpass the power of its cause.
But intellectual knowledge extends beyond sensible things: for we
understand some things which cannot be perceived by the senses.
Therefore intellectual knowledge is not derived from sensible things.
_On the contrary,_ The Philosopher says (Metaph. i, 1; Poster. ii,
15) that the principle of knowledge is in the senses.
_I answer that,_ On this point the philosophers held three opinions.
For Democritus held that "all knowledge is caused by images issuing
from the bodies we think of and entering into our souls," as
Augustine says in his letter to Dioscorus (cxviii, 4). And Aristotle
says (De Somn. et Vigil.) that Democritus held that knowledge is
caused by a "discharge of images." And the reason for this opinion
was that both Democritus and the other early philosophers did not
distinguish between intellect and sense, as Aristotle relates (De
Anima iii, 3). Consequently, since the sense is affected by the
sensible, they thought that all our knowledge is affected by this
mere impression brought about by sensible things. Which impression
Democritus held to be caused by a discharge of images.
Plato, on the other hand, held that the intellect is distinct from
the senses: and that it is an immaterial power not making use of a
corporeal organ for its action. And since the incorporeal cannot be
affected by the corporeal, he held that intellectual knowledge is not
brought about by sensible things affecting the intellect, but by
separate intelligible forms being participated by the intellect, as
we have said above (AA. 4 ,5). Moreover he held that sense is a power
operating of itself. Consequently neither is sense, since it is a
spiritual power, affected by the sensible: but the sensible organs
are affected by the sensible, the result being that the soul is in a
way roused to form within itself the species of the sensible.
Augustine seems to touch on this opinion (Gen. ad lit. xii, 24) where
he says that the "body feels not, but the soul through the body,
which it makes use of as a kind of messenger, for reproducing within
itself what is announced from without." Thus according to Plato,
neither does intellectual knowledge proceed from sensible knowledge,
nor sensible knowledge exclusively from sensible things; but these
rouse the sensible soul to the sentient act, while the senses rouse
the intellect to the act of understanding.
Aristotle chose a middle course. For with Plato he agreed that
intellect and sense are different. But he held that the sense has not
its proper operation without the cooperation of the body; so that to
feel is not an act of the soul alone, but of the "composite." And he
held the same in regard to all the operations of the sensitive part.
Since, therefore, it is not unreasonable that the sensible objects
which are outside the soul should produce some effect in the
"composite," Aristotle agreed with Democritus in this, that the
operations of the sensitive part are caused by the impression of the
sensible on the sense: not by a discharge, as Democritus said, but by
some kind of operation. For Democritus maintained that every
operation is by way of a discharge of atoms, as we gather from _De
Gener._ i, 8. But Aristotle held that the intellect has an operation
which is independent of the body's cooperation. Now nothing corporeal
can make an impression on the incorporeal. And therefore in order to
cause the intellectual operation according to Aristotle, the
impression caused by the sensible does not suffice, but something
more noble is required, for "the agent is more noble than the
patient," as he says (De Gener. i, 5). Not, indeed, in the sense that
the intellectual operation is effected in us by the mere impression
of some superior beings, as Plato held; but that the higher and more
noble agent which he calls the active intellect, of which we have
spoken above (Q. 79, AA. 3, 4) causes the phantasms received from the
senses to be actually intelligible, by a process of abstraction.
According to this opinion, then, on the part of the phantasms,
intellectual knowledge is caused by the senses. But since the
phantasms cannot of themselves affect the passive intellect, and
require to be made actually intelligible by the active intellect, it
cannot be said that sensible knowledge is the total and perfect cause
of intellectual knowledge, but rather that it is in a way the
material cause.
Reply Obj. 1: Those words of Augustine mean that we must not expect
the entire truth from the senses. For the light of the active
intellect is needed, through which we achieve the unchangeable truth
of changeable things, and discern things themselves from their
likeness.
Reply Obj. 2: In this passage Augustine speaks not of intellectual
but of imaginary knowledge. And since, according to the opinion of
Plato, the imagination has an operation which belongs to the soul
only, Augustine, in order to show that corporeal images are impressed
on the imagination, not by bodies but by the soul, uses the same
argument as Aristotle does in proving that the active intellect must
be separate, namely, because "the agent is more noble than the
patient." And without doubt, according to the above opinion, in the
imagination there must needs be not only a passive but also an active
power. But if we hold, according to the opinion of Aristotle, that
the action of the imagination is an action of the "composite," there
is no difficulty; because the sensible body is more noble than the
organ of the animal, in so far as it is compared to it as a being in
act to a being in potentiality; even as the object actually colored
is compared to the pupil which is potentially colored. It may,
however, be said, although the first impression of the imagination is
through the agency of the sensible, since "fancy is movement produced
in accordance with sensation" (De Anima iii, 3), that nevertheless
there is in man an operation which by synthesis and analysis forms
images of various things, even of things not perceived by the senses.
And Augustine's words may be taken in this sense.
Reply Obj. 3: Sensitive knowledge is not the entire cause of
intellectual knowledge. And therefore it is not strange that
intellectual knowledge should extend further than sensitive knowledge.
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