must be made according
to the quantity received.

On the other hand, repayment of a favor belongs, though in different
ways, to friendship and likewise to the virtue of gratitude when it
has the character of a moral debt. For in the repayment of friendship
we have to consider the cause of friendship; so that in the
friendship that is based on the useful, repayment should be made
according to the usefulness accruing from the favor conferred, and in
the friendship based on virtue repayment should be made with regard
for the choice or disposition of the giver, since this is the chief
requisite of virtue, as stated in _Ethic._ viii, 13. And likewise,
since gratitude regards the favor inasmuch as it is bestowed gratis,
and this regards the disposition of the giver, it follows again that
repayment of a favor depends more on the disposition of the giver
than on the effect.

Reply Obj. 1: Every moral act depends on the will. Hence a kindly
action, in so far as it is praiseworthy and is deserving of
gratitude, consists materially in the thing done, but formally and
chiefly in the will. Hence Seneca says (De Benef. i): "A kindly
action consists not in deed or gift, but in the disposition of the
giver or doer."

Reply Obj. 2: Gratitude is a part of justice, not indeed as a species
is part of a genus, but by a kind of reduction to the genus of
justice, as stated above (Q. 80). Hence it does not follow that we
shall find the same kind of debt in both virtues.

Reply Obj. 3: God alone sees man's disposition in itself: but in so
far as it is shown by certain signs, man also can know it. It is thus
that a benefactor's disposition is known by the way in which he does
the kindly action, for instance through his doing it joyfully and
readily.
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SIXTH ARTICLE [II-II, Q. 106, Art. 6]

Whether the Repayment of Gratitude Should Surpass the Favor Received?

Objection 1: It seems that there is no need for the repayment of
gratitude to surpass the favor received. For it is not possible to
make even equal repayment to some, for instance, one's parents, as
the Philosopher states (Ethic. viii, 14). Now virtue does not attempt
the impossible. Therefore gratitude for a favor does not tend to
something yet greater.

Obj. 2: Further, if one person repays another more than he has
received by his favor, by that very fact he gives him something his
turn, as it were. But the latter owes him repayment for the favor
which