In this paragraph from Book Four of Republic,
Plato defines justice as harmony, and connects
it to the self’s unity and activity.
And in truth, justice is, it seems, something
of this sort.
Yet it is not concerned with someone's doing
his own job on the outside.
On the contrary, it is concerned with what
is inside; with himself, really, and the things
that are his own.
It means that he does not allow the elements
in him each to do the job of some other, or
the three sorts of elements in his soul to
meddle with one another.
Instead, he regulates well what is really
his own, rules himself, puts himself in order,
becomes his own friend, and harmonizes the
three elements together, just as if they were
literally the three defining notes of an octave—lowest,
highest, and middle—as well as any others
that may be in between.
He binds together all of these and, from having
been many, becomes entirely one, temperate
and harmonious.
Then and only then should he turn to action,
whether it is to do something concerning the
acquisition of wealth or concerning the care
of his body, or even something political,
or concerning private contracts.
In all these areas, he considers and calls
just and fine the action that preserves this
inner harmony and helps achieve it, and wisdom
the knowledge that oversees such action;
and he considers and calls unjust any action
that destroys this harmony, and ignorance
the belief that oversees it.
