d
inwardly]. This is clear to anyone who considers the difference
between intellect and sense, because sensitive knowledge is concerned
with external sensible qualities, whereas intellective knowledge
penetrates into the very essence of a thing, because the object of the
intellect is "what a thing is," as stated in _De Anima_ iii, 6.

Now there are many kinds of things that are hidden within, to find
which human knowledge has to penetrate within so to speak. Thus, under
the accidents lies hidden the nature of the substantial reality, under
words lies hidden their meaning; under likenesses and figures the
truth they denote lies hidden (because the intelligible world is
enclosed within as compared with the sensible world, which is
perceived externally), and effects lie hidden in their causes, and
vice versa. Hence we may speak of understanding with regard to all
these things.

Since, however, human knowledge begins with the outside of things
as it were, it is evident that the stronger the light of the
understanding, the further can it penetrate into the heart of things.
Now the natural light of our understanding is of finite power;
wherefore it can reach to a certain fixed point. Consequently man
needs a supernatural light in order to penetrate further still so
as to know what it cannot know by its natural light: and this
supernatural light which is bestowed on man is called the gift of
understanding.

Reply Obj. 1: The natural light instilled within us, manifests only
certain general principles, which are known naturally. But since man
is ordained to supernatural happiness, as stated above (Q. 2, A. 3;
I-II, Q. 3, A. 8), man needs to reach to certain higher truths, for
which he requires the gift of understanding.

Reply Obj. 2: The discourse of reason always begins from an
understanding and ends at an understanding; because we reason by
proceeding from certain understood principles, and the discourse of
reason is perfected when we come to understand what hitherto we
ignored. Hence the act of reasoning proceeds from something
previously understood. Now a gift of grace does not proceed from the
light of nature, but is added thereto as perfecting it. Wherefore
this addition is not called "reason" but "understanding," since the
additional light is in comparison with what we know supernaturally,
what the natural light is in regard to those things which we know
from the first.

Reply Obj. 3: "Will" denotes simply a mov