ct of sensation--by instruction or
discovery, to the act of understanding. Wherefore we must say that
the cognitive soul is in potentiality both to the images which are
the principles of sensing, and to those which are the principles of
understanding. For this reason Aristotle (De Anima iii, 4) held that
the intellect by which the soul understands has no innate species,
but is at first in potentiality to all such species.

But since that which has a form actually, is sometimes unable to act
according to that form on account of some hindrance, as a light thing
may be hindered from moving upwards; for this reason did Plato hold
that naturally man's intellect is filled with all intelligible
species, but that, by being united to the body, it is hindered from
the realization of its act. But this seems to be unreasonable. First,
because, if the soul has a natural knowledge of all things, it seems
impossible for the soul so far to forget the existence of such
knowledge as not to know itself to be possessed thereof: for no man
forgets what he knows naturally; that, for instance, the whole is
larger than the part, and such like. And especially unreasonable does
this seem if we suppose that it is natural to the soul to be united
to the body, as we have established above ([Q. 76] , A. 1): for it is
unreasonable that the natural operation of a thing be totally
hindered by that which belongs to it naturally. Secondly, the
falseness of this opinion is clearly proved from the fact that if a
sense be wanting, the knowledge of what is apprehended through that
sense is wanting also: for instance, a man who is born blind can have
no knowledge of colors. This would not be the case if the soul had
innate images of all intelligible things. We must therefore conclude
that the soul does not know corporeal things through innate species.

Reply Obj. 1: Man indeed has intelligence in common with the angels,
but not in the same degree of perfection: just as the lower grades of
bodies, which merely exist, according to Gregory (Homily on
Ascension, xxix In Ev.), have not the same degree of perfection as
the higher bodies. For the matter of the lower bodies is not totally
completed by its form, but is in potentiality to forms which it has
not: whereas the matter of heavenly bodies is totally completed by
its form, so that it is not in potentiality to any other form, as we
have said above (Q. 66, A. 2). In the same way the angelic intellect
is perfe