tuse and unable to pierce. Now a bodily sense, by a kind of
metaphor, is said to pierce the medium, in so far as it perceives its
object from a distance or is able by penetration as it were to
perceive the smallest details or the inmost parts of a thing. Hence
in corporeal things the senses are said to be acute when they can
perceive a sensible object from afar, by sight, hearing, or scent,
while on the other hand they are said to be dull, through being
unable to perceive, except sensible objects that are near at hand, or
of great power.

Now, by way of similitude to bodily sense, we speak of sense in
connection with the intellect; and this latter sense is in respect of
certain primals and extremes, as stated in _Ethic._ vi, even as the
senses are cognizant of sensible objects as of certain principles of
knowledge. Now this sense which is connected with understanding, does
not perceive its object through a medium of corporeal distance, but
through certain other media, as, for instance, when it perceives a
thing's essence through a property thereof, and the cause through its
effect. Consequently a man is said to have an acute sense in
connection with his understanding, if, as soon as he apprehends a
property or effect of a thing, he understands the nature or the thing
itself, and if he can succeed in perceiving its slightest details:
whereas a man is said to have a dull sense in connection with his
understanding, if he cannot arrive at knowing the truth about a
thing, without many explanations; in which case, moreover, he is
unable to obtain a perfect perception of everything pertaining to the
nature of that thing.

Accordingly dulness of sense in connection with understanding denotes
a certain weakness of the mind as to the consideration of spiritual
goods; while blindness of mind implies the complete privation of the
knowledge of such things. Both are opposed to the gift of
understanding, whereby a man knows spiritual goods by apprehending
them, and has a subtle penetration of their inmost nature. This
dulness has the character of sin, just as blindness of mind has, that
is, in so far as it is voluntary, as evidenced in one who, owing to
his affection for carnal things, dislikes or neglects the careful
consideration of spiritual things.

This suffices for the Replies to the Objections.
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THIRD ARTICLE [II-II, Q. 15, Art. 3]

Whether Blindness of Mind and Dulness of Sense Arise from Sins of