[35] for some bodies he has endowed with habit, others with nature, others with soul, and some with rational soul; for instance, he has bound stones and beams, which are torn from their kindred materials, with the most powerful bond of habit; and this habit is the inclination of the spirit to return to itself; for it begins at the middle and [22] proceeds onwards towards the extremities, and then when it has touched the extreme boundary, it turns back again, until it has again arrived at the same place from which it originally started.