exists at all, or that it has motion? On which is founded that reason of Plato's, which is explained by Socrates in the Phædrus, 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."
Now, should all the lower order of philosophers (for so I think they may be called who dissent from Plato and Socrates and that school) unite their force, they never would be able to explain anything so elegantly as this, nor even to understand how ingeniously this conclusion is drawn. The soul, then, perceives itself to have motion,
