" 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