eficiency
of gratitude, because the virtue of gratitude, as stated above (Q.
106, A. 6), inclines to return something more. Wherefore ingratitude
is properly denominated from being a deficiency of gratitude. Now
every deficiency or privation takes its species from the opposite
habit: for blindness and deafness differ according to the difference
of sight and hearing. Therefore just as gratitude or thankfulness is
one special virtue, so also is ingratitude one special sin.

It has, however, various degrees corresponding in their order to the
things required for gratitude. The first of these is to recognize the
favor received, the second to express one's appreciation and thanks,
and the third to repay the favor at a suitable place and time
according to one's means. And since what is last in the order of
generation is first in the order of destruction, it follows that the
first degree of ingratitude is when a man fails to repay a favor, the
second when he declines to notice or indicate that he has received a
favor, while the third and supreme degree is when a man fails to
recognize the reception of a favor, whether by forgetting it or in
any other way. Moreover, since opposite affirmation includes
negation, it follows that it belongs to the first degree of
ingratitude to return evil for good, to the second to find fault with
a favor received, and to the third to esteem kindness as though it
were unkindness.

Reply Obj. 1: In every sin there is material ingratitude to God,
inasmuch as a man does something that may pertain to ingratitude. But
formal ingratitude is when a favor is actually contemned, and this is
a special sin.

Reply Obj. 2: Nothing hinders the formal aspect of some special sin
from being found materially in several kinds of sin, and in this way
the aspect of ingratitude is to be found in many kinds of sin.

Reply Obj. 3: These three are not different species but different
degrees of one special sin.
_______________________

THIRD ARTICLE [II-II, Q. 107, Art. 3]

Whether Ingratitude Is Always a Mortal Sin?

Objection 1: It seems that ingratitude is always a mortal sin. For
one ought to be grateful to God above all. But one is not ungrateful
to God by committing a venial sin: else every man would be guilty of
ingratitude. Therefore no ingratitude is a venial sin.

Obj. 2: Further, a sin is mortal through being contrary to charity,
as stated above (Q. 24, A. 12). But ingratitude is contrary to
charit