Objection 1. It would seem that what was in the body, belonging to the truth of human nature, will not all rise again in it. For food is changed into the truth of human nature. Now sometimes the flesh of the ox or of other animals is taken as food. Therefore if whatever belonged to the truth of human nature will rise again, the flesh of the ox or of other animals will also rise again: which is inadmissible.
Objection 2. Further, Adam's rib belonged to the truth of human nature in him, as ours does in us. But Adam's rib will rise again not in Adam but in Eve, else Eve would not rise again at all since she was made from that rib. Therefore whatever belonged in man to the truth of human nature will not all rise again in him.
Objection 3. Further, it is impossible for the same thing from different men to rise again. Yet it is possible for something in different men to belong to the truth of human nature, for instance if a man were to partake of human flesh which would be changed into his substance. Therefore there will not rise again in man whatever belonged in him to the truth of human nature.
Objection 4. Further, if it be said that not all the flesh partaken of belongs to the truth of human nature and that consequently some of it may possibly rise again in the one man and some in the other--on the contrary: That which is derived from one's parents would especially seem to belong to the truth of human nature. But if one who partook of nothing but human flesh were to beget children that which his child derives from him must needs be of the flesh of other men partaken of by his father, since the seed is from the surplus of food, as the Philosopher proves (De Gen. Animal. i). Therefore what belongs to the truth of human nature in that child belonged also to the truth of human nature in other men of whose flesh his father had partaken.
Objection 5. Further, if it be said that what was changed into seed was not that which belong to the truth of human nature in the flesh of the men eaten, but something not belonging to the truth of human nature--on the contrary: Let us suppose that some one is fed entirely on embryos in which seemingly there is nothing but what belongs to the truth of human nature since whatever is in them is derived from the parents. If then the surplus food be changed into seed, that which belonged to the truth of human nature in the embryos--and after these have received a rational soul, the resurrection applies to them--must needs belong to the truth of human nature in the child begotten of that seed. And thus, since the same cannot rise again in two subjects, it will be impossible for whatever belonged to the truth of human nature in both to rise again in both of them.
On the contrary, Whatever belonged to the truth of human nature was perfected by the rational soul. Now it is through being perfected by the rational soul that the human body is directed to the resurrection. Therefore whatever belonged to the truth of human nature will rise again in each one.
Further, if anything belonging to the truth of human nature in a man be taken from his body, this will not be the perfect body of a man. Now all imperfection of a man will be removed at the resurrection, especially in the elect, to whom it was promised (Luke 21:18) that not a hair of their head should perish. Therefore whatever belonged to the truth of human nature in a man will rise again in him.
I answer that, "Everything is related to truth in the same way as to being" (Metaph. ii), because a thing is true when it is as it appears to him who actually knows it. For this reason Avicenna (Metaph. ii) says that "the truth of anything is a property of the being immutably attached thereto." Accordingly a thing is said to belong to the truth of human nature, because it belongs properly to the being of human nature, and this is what shares the form of human nature, just as true gold is what has the true form of gold whence gold derives its proper being. In order therefore to see what it is that belongs to the truth of human nature, we must observe that there have been three opinions on the question. For some have maintained that nothing begins anew to belong to the truth of human nature and that whatever belongs to the truth of human nature, all of it belonged to the truth of human nature when this was created; and that this multiplies by itself, so that it is possible for the seed whereof the child is begotten to be detached therefrom by the begetter, and that again the detached part multiplies in the child, so that he reaches perfect quantity by growth, and so on, and that thus was the whole human race multiplied. Wherefore according to this opinion, whatever is produced by nourishment. although it seem to have the appearance of flesh and blood, does not belong to the truth of human nature.
Others held that something new is added to the truth of human nature by the natural transformation of the food into the human body, if we consider the truth of human nature in the species to the preservation of which the act of the generative power is directed: but that if we consider the truth of human nature in the individual, to the preservation and perfection of which the act of the nutritive power is directed, that which is added by food belongs to the truth of the human nature of the individual, not primarily but secondarily. For they assert that the truth of human nature, first and foremost, consists in the radical humor, that namely which is begotten of the seed of which the human race was originally fashioned: and that what is changed from food into true flesh and blood does not belong principally to the truth of human nature in this particular individual, but secondarily: and that nevertheless this can belong principally to the truth of human nature in another individual who is begotten of the seed of the former. For they assert that seed is the surplus from food, either mingled with something belonging principally to the truth of human nature in the begetter, according to some, or without any such admixture, as others maintain. And thus the nutrimental humor in one becomes the radical humor in another.
The third opinion is that something new begins to belong principally to the truth of human nature even in this individual, because distinction in the human body does not require that any signate material part must needs remain throughout the whole lifetime; any signate part one may take is indifferent to this, whereas it remains always as regards what belongs to the species in it, albeit as regards what is material therein it may ebb and flow. And thus the nutrimental humor is not distinct from the radical on the part of its principle (so that it be called radical when begotten of the seed, and nutrimental when produced by the food), but rather on the part of the term, so that it be called radical when it reaches the term of generation by the act of the generative, or even nutritive power, but nutrimental, when it has not yet reached this term, but is still on the way to give nourishment.
These three opinions have been more fully exposed and examined in the Second Book (Sent. ii, D, 30); wherefore there is no need for repetition here, except in so far as the question at issue is concerned. It must accordingly be observed that this question requires different answers according to these opinions.
For the first opinion on account of its explanation of the process of multiplication is able to admit perfection of the truth of human nature, both as regards the number of individuals and as regards the due quantity of each individual, without taking into account that which is produced from food; for this is not added except for the purpose of resisting the destruction that might result from the action of natural heat, as lead is added to silver lest it be destroyed in melting. Wherefore since at the resurrection it behooves human nature to be restored to its perfection, nor does the natural heat tend to destroy the natural humor, there will be no need for anything resulting from food to rise again in man, but that alone will rise again which belonged to the truth of the human nature of the individual, and this reaches the aforesaid perfection in number and quantity by being detached and multiplied.
The second opinion, since it maintains that what is produced from food is needed for the perfection of quantity in the individual and for the multiplication that results from generation, must needs admit that something of this product from food shall rise again: not all, however, but only so much as is required for the perfect restoration of human nature in all its individuals. Hence this opinion asserts that all that was in the substance of the seed will rise again in this man who was begotten of this seed; because this belongs chiefly to the truth of human nature in him: while of that which afterwards he derives from nourishment, only so much will rise again in him as is needed for the perfection of his quantity; and not all, because this does not belong to the perfection of human nature, except in so far as nature requires it for the perfection of quantity. Since however this nutrimental humor is subject to ebb and flow the restoration will be effected in this order, that what first belonged to the substance of a man's body, will all be restored, and of that which was added secondly, thirdly, and so on, as much as is required to restore quantity. This is proved by two reasons. First, because that which was added was intended to restore what was wasted at first, and thus it does not belong principally to the truth of human nature to the same extent as that which came first. Secondly, because the addition of extraneous humor to the first radical humors results in the whole mixture not sharing the truth of the specific nature as perfectly as the first did: and the Philosopher instances as an example (De Gener. i) the mixing of water with wine, which always weakens the strength of the wine, so that in the end the wine becomes watery: so that although the second water be drawn into the species of wine, it does not share the species of wine as perfectly as the first water added to the wine. Even so that which is secondly changed from food into flesh does not so perfectly attain to the species of flesh as that which was changed first, and consequently does not belong in the same degree to the truth of human nature nor to the resurrection. Accordingly it is clear that this opinion maintains that the whole of what belongs to the truth of human nature principally will rise again, but not the whole of what belongs to the truth of human nature secondarily.
The third opinion differs somewhat from the second and in some respects agrees with it. It differs in that it maintains that whatever is under the form of flesh and bone all belongs to the truth of human nature, because this opinion does not distinguish as remaining in man during his whole lifetime any signate matter that belongs essentially and primarily to the truth of human nature, besides something ebbing and flowing, that belongs. to the truth of human nature merely on account of the perfection of quantity, and not on account of the primary being of the species, as the second opinion asserted. But it states that all the parts that are not beside the intention of the nature generated belong to the truth of human nature, as regards what they have of the species, since thus they remain; but not as regards what they have of matter, since thus they are indifferent to ebb and flow: so that we are to understand that the same thing happens in the parts of one man as in the whole population of a city, for each individual is cut off from the population by death, while others take their place: wherefore the parts of the people flow back and forth materially, but remain formally, since these others occupy the very same offices and positions from which the former were withdrawn, so that the commonwealth is said to remain the selfsame. In like manner, while certain parts are on the ebb and others are being restored to the same shape and position, all the parts flow back and forth as to their matter, but remain as to their species; and nevertheless the selfsame man remains.
On the other hand, The third opinion agrees with the second, because it holds that the parts which come secondly do not reach the perfection of the species so perfectly as those which come first: and consequently the third opinion asserts that the same thing rises again in man as the second opinion maintains, but not for quite the same reason. For it holds that the whole of what is produced from the seed will rise again, not because it belongs to the truth of human nature otherwise than that which comes after, but because it shares the truth of human nature more perfectly: which same order the second opinion applied to those things that are produced afterwards from food, in which point also these two opinions agree.
Reply to Objection 1. A natural thing is what it is, not from its matter but from its form; wherefore, although that part of matter which at one time was under the form of bovine flesh rises again in man under the form of human flesh, it does not follow that the flesh of an ox rises again, but the flesh of a man: else one might conclude that the clay from which Adam's body was fashioned shall rise again. The second opinion, however, grants this argument.
Reply to Objection 2. That rib did not belong to the perfection of the individual in Adam, but was directed to the multiplication of the species. Hence it will rise again not in Adam but in Eve, just as the seed will rise again, not in the begetter, but in the begotten.
Reply to Objection 3. According to the first opinion it is easy to reply to this argument, because the flesh that is eaten never belonged to the truth of human nature in the eater, but it did belong to the truth of human nature in him whose flesh was eaten: and thus it will rise again in the latter but not in the former. according to the second and third opinions, each one will rise again in that wherein he approached nearest to the perfect participation of the virtue of the species, and if he approached equally in both, he will rise again in that wherein he was first, because in that he first was directed to the resurrection by union with the rational soul of that man. Hence if there were any surplus in the flesh eaten, not belonging to the truth of human nature in the first man, it will be possible for it to rise again in the second: otherwise what belonged to the resurrection in the first will rise again in him and not in the second; but in the second its place is taken either by something of that which was the product from other food, or if he never partook of any other food than human flesh, the substitution is made by Divine power so far as the perfection of quantity requires, as it does in those who die before the perfect age. Nor does this derogate from numerical identity, as neither does the ebb and flow of parts.
Reply to Objection 4. According to the first opinion this argument is easily answered. For that opinion asserts that the seed is not from the surplus food: so that the flesh eaten is not changed into the seed whereof the child is begotten. But according to the other two opinions we must reply that it is impossible for the whole of the flesh eaten to be changed into seed, because it is after much separation that the seed is distilled from the food, since seed is the ultimate surplus of food. That part of the eaten flesh which is changed into seed belongs to the truth of human nature in the one born of the seed more than in the one of whose flesh the seed was the product. Hence according to the rule already laid down (ad 3), whatever was changed into the seed will rise again in the person born of the seed; while the remaining matter will rise again in him of whose flesh the seed was the product.
Reply to Objection 5. The embryo is not concerned with the resurrection before it is animated by a rational soul, in which state much has been added to the seminal substance from the substance of food, since the child is nourished in the mother's womb. Consequently on the supposition that a man partook of such food, and that some one were begotten of the surplus thereof, that which was in the seminal substance will indeed rise again in the one begotten of that seed; unless it contain something that would have belonged to the seminal substance in those from whose flesh being eaten the seed was produced, for this would rise again in the first but not in the second. The remainder of the eaten flesh, not being changed into seed, will clearly rise again in the first the Divine power supplying deficiencies in both. The first opinion is not troubled by this objection, since it does not hold the seed to be from the surplus food: but there are many other reasons against it as may be seen in the Second Book (Sent. ii, D, 30; I, 119, 2).
Source: Summa Theologica (New Advent)