Reply. The power of a thing does not extend to the past, but to the present or future: hence with regard to past events possibility has no place. Therefore from the fact of the soul having a power of being always it does not follow that the soul always has been, but that it always will be. -- Besides, that to which power extends does not follow until the power is presupposed. It cannot therefore be concluded that the soul is always except for the time that comes after it has received the power.
Arg. 2. Truth of the intllectual order is imperishable, eternal, necessary. Now from the imperishableness of intellectual truth the being of the soul is shown to be imperishable. In like manner from the eternity of that truth there may be proved the eternity of the soul.
Reply. The eternity of understood truth may be regarded in two ways, -- in point of the object which is understood, and in point of the mind whereby it is understood. From the eternity of understood truth in point of the object, there will follow the eternity of the thing, but not the eternity of the thinker. From the eternity of understood truth in point of the understanding mind, the eternity of that thinking soul will follow. But understood truth is eternal, not in the latter but in the former way. As we have seen, the intellectual impressions, whereby our soul understands truth, come to us fresh from the phantasms through the medium of the active intellect. Hence the conclusion is, not that our soul is eternal, but that those understood truths are founded upon something which is eternal. In fact they are founded upon the First Truth, the universal Cause comprehensive of all truth. To this truth our soul stands related, not as the recipient subject to the form which it receives, but as a thing to its proper end: for truth is the good of the understanding and the end thereof. Now we can gather an argument of the duration of a thing from its end, as we can argue the beginning of a thing from its efficient cause: for what is ordained to an everlasting end must be capable of perpetual duration. Hence the immortality of the soul may be argued from the eternity of intellectual truth, but not the eternity of the soul.
Arg. 3. That is not perfect, to which many of its principal parts are wanting. If therefore there daily begin to be as many human souls as there are men born, it is clear that many of its principal parts are daily being added to the universe, and consequently that very many are still wanting to it. It follows that the universe is imperfect, which is impossible.*
Reply. The perfection of the universe goes by species, not by individuals; and human souls do not differ in species, but only in number (Chap. LXXV).
(B.) Some professing the Catholic faith, but imbued with Platonic doctrines, have taken a middle course [between Platonists, who held that individual souls were from eternity, now united with bodies, now released by turns; and Alexander, Averroes, -- and possibly Aristotle himself, -- deniers of personal immortality]. These men, seeing that according to the Catholic faith nothing is eternal but God, have supposed human souls not to be eternal, but to have been created with the world, or rather before the visible world, and to be united with bodies recurrently as required. Origen was the first professor of the Christian faith to take up this position, and he has since had many followers. The position seems assailable on these grounds.
1. The soul is united with the body as the form and actualising principle thereof. Now though actuality is naturally prior to potentiality, yet, in the same subject, it is posterior to it in time:* for a thing moves from potentiality to actuality. Therefore the seed, which is potentially alive, was before the soul, which is the actuality of life.
2. It is natural to every form to be united to its own proper matter: otherwise the compound of matter and form would be something unnatural. Now that which belongs to a thing according to its nature is assigned to it before that which belongs to it against its nature: for what belongs to a thing against its nature attaches to it incidentally, but what belongs to it according to its nature attaches to it ordinarily; and the incidental is always posterior to the ordinary. It belongs to the soul therefore to be united to the body before being apart from the body.
3. Every part, separated from its whole, is imperfect. But the soul, being the form (Chap. XLVII), is a part of the human species. Therefore, existing by itself, apart from the body, it is imperfect. But the perfect is before the imperfect in the order of natural things.*
(C.) If souls were created without bodies, the question arises how they came to be united with bodies. It must have been either violently or naturally. If violently, the union of the soul with the body is unnatural, and man is an unnatural compound of soul and body, which cannot be true. But if souls are naturally united with bodies, then they were created with a physical tendency (appetitus naturalis) to such union. Now a physical tendency works itself out at once, unless something comes in the way. Souls then should have been united with bodies from the instant of their creation except for some intervening obstacle. But any obstacle intervening to arrest a physical tendency, or natural craving, does violence to the same. Therefore it would have been by violence that souls were for a period separated from their bodies, which is an awkward conclusion.*
(D.) But if it be said that both states alike are natural to the soul, as well the state of union with the body as the state of separation, according to difference of times, this appears to be impossible, -- because points of natural variation are accidents to the subject in which they occur, as age and youth: if then union with body and separation from a body are natural variations to the soul, the union of the soul with the body will be an accident; and man, the result of that union, will not be an ordinary, regular entity (ens per se), but a casual, incidental being (ens per accidens).
(E.) But if it is said that souls are united with bodies neither violently nor naturally, but of their own spontaneous will, that cannot be. For none is willing to come to a worse state except under deception. But the soul is in a higher state away from the body, especially according to the Platonists, who say that by union with the body the soul suffers forgetfulness of what it knew before, and is hindered from the contemplation of pure truth. At that rate it has no willingness to be united with a body except for some deceit practised upon it. Threfore, supposing it to have pre-existed before the body, it would not be united therewith of its own accord.
(F.) But if as an alternative it is said that the soul is united with the body neither by nature, nor by its own will, but by a divine ordinance, this again does not appear a suitable arrangement, on the supposition that souls were created before bodies. For God has established everything according to the proper mode of its nature: hence it is said: God saw all things that he had made, and they were very good (Gen. i, 31). If then He created souls apart from bodies, we must say that this mode of being is better suited to their nature. But it is not proper for an ordinance of divine goodness to reduce things to a lower state, but rather to rise them to a higher. At that rate the union of soul with body could not be the result of a divine ordinance.
(G.) This consideration moved Origen to suppose that when souls, created from the beginning of time, came by divine ordinance to be united with bodies, it was for their punishment. He supposed that they had sinned before they came into bodies, and that according to the amount of their guilt they were united with bodies of various degrees of nobility, shut up in them as in prisons. But this supposition cannot stand for reasons alleged above (Chap. XLIV).
2.82 : That the Souls of Dumb Animals are not Immortal
2.85 : That the Soul is not of the Substance of God