merely bodies; nor, when I say these things to you, am I
addressing myself to your body: when, therefore, he says, "Know yourself,"
he says this, "Inform yourself of the nature of your soul;" for the body
is but a kind of vessel, or receptacle of the soul, and whatever your soul
does is your own act. To know the soul, then, unless it had been divine,
would not have been a precept of such excellent wisdom, as to be
attributed to a god; but even though the soul should not know of what
nature itself is, will you say that it does not even perceive that it
exists at all, or that it has motion? on which is founded that reason of
Plato's, which is explained by Socrates in the Phaedrus, and inserted by
me, in my sixth book of the Republic.

XXIII. "That which is always moved is eternal; but that which gives motion
to something else, and is moved itself by some external cause, when that
motion ceases, must necessarily cease to exist. That, therefore, alone,
which is self-moved, because it is never forsaken by itself, can never
cease to be moved. Besides, it is the beginning and principle of motion to
everything else; but whatever is a principle has no beginning, for all
things arise from that principle, and it cannot itself owe its rise to
anything else; for then it would not be a principle did it proceed from
anything else. But if it has no beginning, it never will have any end; for
a principle which is once extinguished, cannot itself be restored by
anything else, nor can it produce anything else from itself; inasmuch as
all things must necessarily arise from some first cause. And thus it comes
about, that the first principle of motion must arise from that thing which
is itself moved by itself; and that can neither have a beginning nor an
end of its existence, for otherwise the whole heaven and earth would be
overset, and all nature would stand still, and not be able to acquire any
force, by the impulse of which it might be first set in motion. Seeing,
then, that it is clear, that whatever moves itself is eternal, can there
be any doubt that the soul is so? For everything is inanimate which is
moved by an external force; but everything which is animate is moved by an
interior force, which also belongs to itself. For this is the peculiar
nature and power of the soul; and if the soul be the only thing in the
whole world which has the power of self-motion, then certainly it never
had a beginning, and therefore it is eternal."

N