the knowledge of incorporeal things." But these are the
immaterial substances. Therefore the human mind understands immaterial
substances.

Obj. 2: Further, like is known by like. But the human mind is more
akin to immaterial than to material things; since its own nature is
immaterial, as is clear from what we have said above (Q. 76, A. 1).
Since then our mind understands material things, much more is it able
to understand immaterial things.

Obj. 3: Further, the fact that objects which are in themselves most
sensible are not most felt by us, comes from sense being corrupted by
their very excellence. But the intellect is not subject to such a
corrupting influence from its object, as is stated _De Anima_ iii, 4.
Therefore things which are in themselves in the highest degree of
intelligibility, are likewise to us most intelligible. As material
things, however, are intelligible only so far as we make them
actually so by abstracting them from material conditions, it is clear
that those substances are more intelligible in themselves whose
nature is immaterial. Therefore they are much more known to us than
are material things.

Obj. 4: Further, the Commentator says (Metaph. ii) that "nature would
be frustrated in its end" were we unable to understand abstract
substances, "because it would have made what in itself is naturally
intelligible not to be understood at all." But in nature nothing is
idle or purposeless. Therefore immaterial substances can be
understood by us.

Obj. 5: Further, as sense is to the sensible, so is intellect to the
intelligible. But our sight can see all things corporeal, whether
superior and incorruptible; or lower and corruptible. Therefore our
intellect can understand all intelligible substances, even the
superior and immaterial.

_On the contrary,_ It is written (Wis. 9:16): "The things that are in
heaven, who shall search out?" But these substances are said to be in
heaven, according to Matt. 18:10, "Their angels in heaven," etc.
Therefore immaterial substances cannot be known by human
investigation.

_I answer that,_ In the opinion of Plato, immaterial substances are
not only understood by us, but are the objects we understand first
of all. For Plato taught that immaterial subsisting forms, which he
called "Ideas," are the proper objects of our intellect, and thus
first and _per se_ understood by us; and, further, that material
objects are known by the soul inasmuch as phantasy and sense