y, since the debt of gratitude proceeds from that virtue, as
stated above (Q. 106, A. 1, ad 3; A. 6, ad 2). Therefore ingratitude
is always a mortal sin.

Obj. 3: Further, Seneca says (De Benef. ii): "Between the giver and
the receiver of a favor there is this law, that the former should
forthwith forget having given, and the latter should never forget
having received." Now, seemingly, the reason why the giver should
forget is that he may be unaware of the sin of the recipient, should
the latter prove ungrateful; and there would be no necessity for that
if ingratitude were a slight sin. Therefore ingratitude is always a
mortal sin.

Obj. 4: _On the contrary,_ No one should be put in the way of
committing a mortal sin. Yet, according to Seneca (De Benef. ii),
"sometimes it is necessary to deceive the person who receives
assistance, in order that he may receive without knowing from whom he
has received." But this would seem to put the recipient in the way of
ingratitude. Therefore ingratitude is not always a mortal sin.

_I answer that,_ As appears from what we have said above (A. 2), a
man may be ungrateful in two ways: first, by mere omission, for
instance by failing to recognize the favor received, or to express
his appreciation of it or to pay something in return, and this is not
always a mortal sin, because, as stated above (Q. 106, A. 6), the
debt of gratitude requires a man to make a liberal return, which,
however, he is not bound to do; wherefore if he fail to do so, he
does not sin mortally. It is nevertheless a venial sin, because it
arises either from some kind of negligence or from some
disinclination to virtue in him. And yet ingratitude of this kind may
happen to be a mortal sin, by reason either of inward contempt, or of
the kind of thing withheld, this being needful to the benefactor,
either simply, or in some case of necessity.

Secondly, a man may be ungrateful, because he not only omits to pay
the debt of gratitude, but does the contrary. This again is sometimes
a mortal and sometimes a venial sin, according to the kind of thing
that is done.

It must be observed, however, that when ingratitude arises from a
mortal sin, it has the perfect character of ingratitude, and when it
arises from venial sin, it has the imperfect character.

Reply Obj. 1: By committing a venial sin one is not ungrateful to God
to the extent of incurring the guilt of perfect ingratitude: but
there is something of ingratitu