The Complete Aristotle (eng.)

that both the unjust man and the unjust act
are unfair or unequal; now it is clear that there is also an
intermediate between the two unequals involved in either case. And
this is the equal; for in any kind of action in which there’s a
more and a less there is also what is equal. If, then, the unjust
is unequal, just is equal, as all men suppose it to be, even apart
from argument. And since the equal is intermediate, the just will
be an intermediate. Now equality implies at least two things. The
just, then, must be both intermediate and equal and relative (i.e.
for certain persons). And since the equall intermediate it must be
between certain things (which are respectively greater and less);
equal, it involves two things; qua just, it is for certain people.
The just, therefore, involves at least four terms; for the persons
for whom it is in fact just are two, and the things in which it is
manifested, the objects distributed, are two. And the same equality
will exist between the persons and between the things concerned;
for as the latter the things concerned-are related, so are the
former; if they are not equal, they will not have what is equal,
but this is the origin of quarrels and complaints-when either
equals have and are awarded unequal shares, or unequals equal
shares. Further, this is plain from the fact that awards should be
‘according to merit’; for all men agree that what is just in
distribution must be according to merit in some sense, though they
do not all specify the same sort of merit, but democrats identify
it with the status of freeman, supporters of oligarchy with wealth
(or with noble birth), and supporters of aristocracy with
excellence.
    The just, then, is a species of the proportionate (proportion
being not a property only of the kind of number which consists of
abstract units, but of number in general). For proportion is
equality of ratios, and involves four terms at least (that discrete
proportion involves four terms is plain, but so does continuous
proportion, for it uses one term as two and mentions it twice; e.g.
‘as the line A is to the line B, so is the line B to the line C’;
the line B, then, has been mentioned twice, so that if the line B
be assumed twice, the proportional terms will be four); and the
just, too, involves at least four terms, and the ratio between one
pair is the same as that between the other pair; for there is a
similar distinction between the persons and between the things. As
the term A, then, is to B, so will C be to D, and therefore,
alternando, as A is to C, B will be to D. Therefore also the whole
is in the same ratio to the whole; and this coupling the
distribution effects, and, if the terms are so combined, effects
justly. The conjunction, then, of the term A with C and of B with D
is what is just in distribution, and this species of the just is
intermediate, and the unjust is what violates the proportion; for
the proportional is intermediate, and the just is proportional.
(Mathematicians call this kind of proportion geometrical; for it is
in geometrical proportion that it follows that the whole is to the
whole as either part is to the corresponding part.) This proportion
is not continuous; for we cannot get a single term standing for a
person and a thing.
    This, then, is what the just is-the proportional; the unjust is
what violates the proportion. Hence one term becomes too great, the
other too small, as indeed happens in practice; for the man who
acts unjustly has too much, and the man who is unjustly treated too
little, of what is good. In the case of evil the reverse is true;
for the lesser evil is reckoned a good in comparison with the
greater evil, since the lesser evil is rather to be chosen than the
greater, and what is worthy of choice is good, and what is worthier
of choice a greater good.
    This, then, is one species of the just.
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    (B) The remaining one is the rectificatory, which arises in
connexion with transactions both voluntary and involuntary. This
form of the just has a different specific character from the
former. For the justice which distributes common possessions is
always in accordance with the kind of proportion mentioned above
(for in the case also in which the distribution is made from the
common funds of a partnership it will be according to the same
ratio which the funds put into the business by the partners bear to
one another); and the injustice opposed to this kind of justice is
that