"Since it was clear to Plato that the soul is assigned to substance, and that substance is predicated on the form and matter which is body, and that the soul cannot be said to be a body, he fervently defined the soul in its particular aspect. Since he had established that the forms of spheres are souls, he looked for the commonality of all [souls], and found that sense perception is particular to animals, [but] that movement is particular to all, and therefore he defined the soul as “something which moves itself."