The Complete Aristotle (eng.)

to goods-it is
not always worth the same; yet it tends to be steadier. This is why
all goods must have a price set on them; for then there will always
be exchange, and if so, association of man with man. Money, then,
acting as a measure, makes goods commensurate and equates them; for
neither would there have been association if there were not
exchange, nor exchange if there were not equality, nor equality if
there were not commensurability. Now in truth it is impossible that
things differing so much should become commensurate, but with
reference to demand they may become so sufficiently. There must,
then, be a unit, and that fixed by agreement (for which reason it
is called money); for it is this that makes all things
commensurate, since all things are measured by money. Let A be a
house, B ten minae, C a bed. A is half of B, if the house is worth
five minae or equal to them; the bed, C, is a tenth of B; it is
plain, then, how many beds are equal to a house, viz. five. That
exchange took place thus before there was money is plain; for it
makes no difference whether it is five beds that exchange for a
house, or the money value of five beds.
    We have now defined the unjust and the just. These having been
marked off from each other, it is plain that just action is
intermediate between acting unjustly and being unjustly treated;
for the one is to have too much and the other to have too little.
Justice is a kind of mean, but not in the same way as the other
virtues, but because it relates to an intermediate amount, while
injustice relates to the extremes. And justice is that in virtue of
which the just man is said to be a doer, by choice, of that which
is just, and one who will distribute either between himself and
another or between two others not so as to give more of what is
desirable to himself and less to his neighbour (and conversely with
what is harmful), but so as to give what is equal in accordance
with proportion; and similarly in distributing between two other
persons. Injustice on the other hand is similarly related to the
unjust, which is excess and defect, contrary to proportion, of the
useful or hurtful. For which reason injustice is excess and defect,
viz. because it is productive of excess and defect-in one’s own
case excess of what is in its own nature useful and defect of what
is hurtful, while in the case of others it is as a whole like what
it is in one’s own case, but proportion may be violated in either
direction. In the unjust act to have too little is to be unjustly
treated; to have too much is to act unjustly.
    Let this be taken as our account of the nature of justice and
injustice, and similarly of the just and the unjust in general.
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6
    Since acting unjustly does not necessarily imply being unjust,
we must ask what sort of unjust acts imply that the doer is unjust
with respect to each type of injustice, e.g. a thief, an adulterer,
or a brigand. Surely the answer does not turn on the difference
between these types. For a man might even lie with a woman knowing
who she was, but the origin of his might be not deliberate choice
but passion. He acts unjustly, then, but is not unjust; e.g. a man
is not a thief, yet he stole, nor an adulterer, yet he committed
adultery; and similarly in all other cases.
    Now we have previously stated how the reciprocal is related to
the just; but we must not forget that what we are looking for is
not only what is just without qualification but also political
justice. This is found among men who share their life with a view
to selfsufficiency, men who are free and either proportionately or
arithmetically equal, so that between those who do not fulfil this
condition there is no political justice but justice in a special
sense and by analogy. For justice exists only between men whose
mutual relations are governed by law; and law exists for men
between whom there is injustice; for legal justice is the
discrimination of the just and the unjust. And between men between
whom there is injustice there is also unjust action (though there
is not injustice between all between whom there is unjust action),
and this is assigning too much to oneself of things good in
themselves and too little of things evil in themselves. This is why
we do not allow a man to rule, but rational principle, because a
man behaves thus in his own interests and becomes a tyrant. The
magistrate on the other hand is the guardian of justice, and, if of
justice, then of