ue must needs be defined by means of
the good act bearing on the matter proper to that virtue. Now the
proper matter of justice consists of those things that belong to our
intercourse with other men, as shall be shown further on (A. 2).
Hence the act of justice in relation to its proper matter and object
is indicated in the words, "Rendering to each one his right," since,
as Isidore says (Etym. x), "a man is said to be just because he
respects the rights (_jus_) of others."

Now in order that an act bearing upon any matter whatever be
virtuous, it requires to be voluntary, stable, and firm, because the
Philosopher says (Ethic. ii, 4) that in order for an act to be
virtuous it needs first of all to be done "knowingly," secondly to be
done "by choice," and "for a due end," thirdly to be done
"immovably." Now the first of these is included in the second, since
"what is done through ignorance is involuntary" (Ethic. iii, 1).
Hence the definition of justice mentions first the "will," in order
to show that the act of justice must be voluntary; and mention is
made afterwards of its "constancy" and "perpetuity" in order to
indicate the firmness of the act.

Accordingly, this is a complete definition of justice; save that the
act is mentioned instead of the habit, which takes its species from
that act, because habit implies relation to act. And if anyone would
reduce it to the proper form of a definition, he might say that
"justice is a habit whereby a man renders to each one his due by a
constant and perpetual will": and this is about the same definition
as that given by the Philosopher (Ethic. v, 5) who says that "justice
is a habit whereby a man is said to be capable of doing just actions
in accordance with his choice."

Reply Obj. 1: Will here denotes the act, not the power: and it is
customary among writers to define habits by their acts: thus
Augustine says (Tract. in Joan. xl) that "faith is to believe what
one sees not."

Reply Obj. 2: Justice is the same as rectitude, not essentially but
causally; for it is a habit which rectifies the deed and the will.

Reply Obj. 3: The will may be called perpetual in two ways. First on
the part of the will's act which endures for ever, and thus God's
will alone is perpetual. Secondly on the part of the subject,
because, to wit, a man wills to do a certain thing always, and this
is a necessary condition of justice. For it does not satisfy the
conditions of justice that one wish