that,_ We speak of merit and demerit, in relation to
retribution, rendered according to justice. Now, retribution
according to justice is rendered to a man, by reason of his having
done something to another's advantage or hurt. It must, moreover, be
observed that every individual member of a society is, in a fashion,
a part and member of the whole society. Wherefore, any good or evil,
done to the member of a society, redounds on the whole society: thus,
who hurts the hand, hurts the man. When, therefore, anyone does good
or evil to another individual, there is a twofold measure of merit or
demerit in his action: first, in respect of the retribution owed to
him by the individual to whom he has done good or harm; secondly, in
respect of the retribution owed to him by the whole of society. Now
when a man ordains his action directly for the good or evil of the
whole society, retribution is owed to him, before and above all, by
the whole society; secondarily, by all the parts of society. Whereas
when a man does that which conduces to his own benefit or
disadvantage, then again is retribution owed to him, in so far as
this too affects the community, forasmuch as he is a part of society:
although retribution is not due to him, in so far as it conduces to
the good or harm of an individual, who is identical with the agent:
unless, perchance, he owe retribution to himself, by a sort of
resemblance, in so far as man is said to be just to himself.

It is therefore evident that a good or evil action deserves praise or
blame, in so far as it is in the power of the will: that it is right
or sinful, according as it is ordained to the end; and that its merit
or demerit depends on the recompense for justice or injustice towards
another.

Reply Obj. 1: A man's good or evil actions, although not ordained to
the good or evil of another individual, are nevertheless ordained to
the good or evil of another, i.e. the community.

Reply Obj. 2: Man is master of his actions; and yet, in so far as he
belongs to another, i.e. the community, of which he forms part, he
merits or demerits, inasmuch as he disposes his actions well or ill:
just as if he were to dispense well or ill other belongings of his,
in respect of which he is bound to serve the community.

Reply Obj. 3: This very good or evil, which a man does to himself by
his action, redounds to the community, as stated above.
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FOURTH ARTICLE [I-II, Q. 21, Art. 4]