The Divine Institutes

There follows another, and in itself an inexplicable inquiry: Whether the soul and the mind are the same, or there be one faculty by which we live, and another by which we perceive and have discernment. There are not wanting arguments on either side. For they who say that they are one faculty make use of this argument, that we cannot live without perception, nor perceive without life, and therefore that that which is incapable of separation cannot be different; but that whatever it is, it has the office of living and the method of perception. On which account two Epicurean poets speak of the mind and the soul indifferently. But they who say that they are different argue in this way: That the mind is one thing, and the soul another, may be understood from this, that the mind may be extinguished while the soul is uninjured, which is accustomed to happen in the case of the insane; also, that the soul is put to rest by death, the mind by sleep, and indeed in such a manner that it is not only ignorant of what is taking place, or where it is, but it is even deceived by the contemplation of false objects. And how this takes place cannot accurately be perceived; why it takes place can be perceived. For we can by no means rest unless the mind is kept occupied by the similitudes of visions. But the mind lies hid, oppressed with sleep, as fire buried by ashes drawn over it; but if you stir it a little it again blazes, and, as it were, wakes up. Therefore it is called away by images, until the limbs, bedewed with sleep, are invigorated; for the body while the perception is awake, although it lies motionless, yet is not at rest, because the perception burns in it, and vibrates as a flame, and keeps all the limbs bound to itself.

But when the mind is transferred from its application to the contemplation of images, then at length the whole body is resolved into rest. But the mind is transferred from dark thought, when, under the influence of darkness, it has begun to be alone with itself. While it is intent upon those things concerning which it is reflecting, sleep suddenly creeps on, and the thought itself imperceptibly turns aside to the nearest appearances: thus it begins also to see those things which it had placed before its eyes. Then it proceeds further, and finds diversions for itself, that it may not interrupt the most healthy repose of the body. For as the mind is diverted in the day by true sights, so that it does not sleep; so is it diverted in the night by false sights, so that it is not aroused. For if it perceives no images, it will follow of necessity either that it is awake, or that it is asleep in perpetual death. Therefore the system of dreaming has been given by God for the sake of sleeping; and, indeed, it has been given to all animals in common; but this especially to man, that when God gave this system on account of rest, He left to Himself the power of teaching man future events by means of the dream. For narratives often testify that there have been dreams which have had an immediate and a remarkable accomplishment, and the answers of our prophets have been after the character of a dream. On which account they are not always true, nor always false, as Virgil testified, who supposed that there were two gates for the passage of dreams. But those which are false are seen for the sake of sleeping; those which are true are sent by God, that by this revelation we may learn impending goods or evils.