(1) Whether the sensitive soul is transmitted with the semen?
(2) Whether the intellectual soul is thus transmitted?
(3) Whether all souls were created at the same time?
Whether the Sensitive Soul Is Transmitted with the Semen?
Objection 1: It would seem that the sensitive soul is not transmitted with the semen, but created by God. For every perfect substance, not composed of matter and form, that begins to exist, acquires existence not by generation, but by creation: for nothing is generated save from matter. But the sensitive soul is a perfect substance, otherwise it could not move the body; and since it is the form of a body, it is not composed of matter and form. Therefore it begins to exist not by generation but by creation.
Obj. 2: Further, in living things the principle of generation is the generating power; which, since it is one of the powers of the vegetative soul, is of a lower order than the sensitive soul. Now nothing acts beyond its species. Therefore the sensitive soul cannot be caused by the animal's generating power.
Obj. 3: Further, the generator begets its like: so that the form of the generator must be actually in the cause of generation. But neither the sensitive soul itself nor any part thereof is actually in the semen, for no part of the sensitive soul is elsewhere than in some part of the body; while in the semen there is not even a particle of the body, because there is not a particle of the body which is not made from the semen and by the power thereof. Therefore the sensitive soul is not produced through the semen.
Obj. 4: Further, if there be in the semen any principle productive of the sensitive soul, this principle either remains after the animal is begotten, or it does not remain. Now it cannot remain. For either it would be identified with the sensitive soul of the begotten animal; which is impossible, for thus there would be identity between begetter and begotten, maker and made: or it would be distinct therefrom; and again this is impossible, for it has been proved above (Q. 76, A. 4) that in one animal there is but one formal principle, which is the soul. If on the other hand the aforesaid principle does not remain, this again seems to be impossible: for thus an agent would act to its own destruction, which cannot be. Therefore the sensitive soul cannot be generated from the semen.
_On the contrary,_ The power in the semen is to the animal seminally generated, as the power in the elements of the world is to animals produced from these elements--for instance by putrefaction. But in the latter animals the soul is produced by the elemental power, according to Gen. 1:20: "Let the waters bring forth the creeping creatures having life." Therefore also the souls of animals seminally generated are produced by the seminal power.
_I answer that,_ Some have held that the sensitive souls of animals are created by God (Q. 65, A. 4). This opinion would hold if the sensitive soul were subsistent, having being and operation of itself.
For thus, as having being and operation of itself, to be made would needs be proper to it. And since a simple and subsistent thing cannot be made except by creation, it would follow that the sensitive soul would arrive at existence by creation.
But this principle is false--namely, that being and operation are proper to the sensitive soul, as has been made clear above (Q. 75, A. 3): for it would not cease to exist when the body perishes. Since, therefore, it is not a subsistent form, its relation to existence is that of the corporeal forms, to which existence does not belong as proper to them, but which are said to exist forasmuch as the subsistent composites exist through them.
Wherefore to be made is proper to composites. And since the generator is like the generated, it follows of necessity that both the sensitive soul, and all other like forms are naturally brought into existence by certain corporeal agents that reduce the matter from potentiality to act, through some corporeal power of which they are possessed.
Now the more powerful an agent, the greater scope its action has: for instance, the hotter a body, the greater the distance to which its heat carries. Therefore bodies not endowed with life, which are the lowest in the order of nature, generate their like, not through some medium, but by themselves; thus fire by itself generates fire. But living bodies, as being more powerful, act so as to generate their like, both without and with a medium. Without a medium--in the work of nutrition, in which flesh generates flesh: with a medium--in the act of generation, because the semen of the animal or plant derives a certain active force from the soul of the generator, just as the instrument derives a certain motive power from the principal agent.
And as it matters not whether we say that something is moved by the instrument or by the principal agent, so neither does it matter whether we say that the soul of the generated is caused by the soul of the generator, or by some seminal power derived therefrom.
Reply Obj. 1: The sensitive soul is not a perfect self-subsistent substance. We have said enough (Q. 25, A. 3) on this point, nor need we repeat it here.
Reply Obj. 2: The generating power begets not only by its own virtue but by that of the whole soul, of which it is a power. Therefore the generating power of a plant generates a plant, and that of an animal begets an animal. For the more perfect the soul is, to so much a more perfect effect is its generating power ordained.
Reply Obj. 3: This active force which is in the semen, and which is derived from the soul of the generator, is, as it were, a certain movement of this soul itself: nor is it the soul or a part of the soul, save virtually; thus the form of a bed is not in the saw or the axe, but a certain movement towards that form. Consequently there is no need for this active force to have an actual organ; but it is based on the (vital) spirit in the semen which is frothy, as is attested by its whiteness. In which spirit, moreover, there is a certain heat derived from the power of the heavenly bodies, by virtue of which the inferior bodies also act towards the production of the species as stated above (Q. 115, A. 3, ad 2). And since in this (vital) spirit the power of the soul is concurrent with the power of a heavenly body, it has been said that "man and the sun generate man." Moreover, elemental heat is employed instrumentally by the soul's power, as also by the nutritive power, as stated (De Anima ii, 4).
Reply Obj. 4: In perfect animals, generated by coition, the active force is in the semen of the male, as the Philosopher says (De Gener.
Animal. ii, 3); but the foetal matter is provided by the female. In this matter, the vegetative soul exists from the very beginning, not as to the second act, but as to the first act, as the sensitive soul is in one who sleeps. But as soon as it begins to attract nourishment, then it already operates in act. This matter therefore is transmuted by the power which is in the semen of the male, until it is actually informed by the sensitive soul; not as though the force itself which was in the semen becomes the sensitive soul; for thus, indeed, the generator and generated would be identical; moreover, this would be more like nourishment and growth than generation, as the Philosopher says. And after the sensitive soul, by the power of the active principle in the semen, has been produced in one of the principal parts of the thing generated, then it is that the sensitive soul of the offspring begins to work towards the perfection of its own body, by nourishment and growth. As to the active power which was in the semen, it ceases to exist, when the semen is dissolved and the (vital) spirit thereof vanishes. Nor is there anything unreasonable in this, because this force is not the principal but the instrumental agent; and the movement of an instrument ceases when once the effect has been produced.
Whether the Intellectual Soul Is Produced from the Semen?
Objection 1: It would seem that the intellectual soul is produced from the semen. For it is written (Gen. 46:26): "All the souls that came out of [Jacob's] thigh, sixty-six." But nothing is produced from the thigh of a man, except from the semen. Therefore the intellectual soul is produced from the semen.
Obj. 2: Further, as shown above (Q. 76, A. 3), the intellectual, sensitive, and nutritive souls are, in substance, one soul in man.
But the sensitive soul in man is generated from the semen, as in other animals; wherefore the Philosopher says (De Gener. Animal. ii, 3) that the animal and the man are not made at the same time, but first of all the animal is made having a sensitive soul. Therefore also the intellectual soul is produced from the semen.
Obj. 3: Further, it is one and the same agent whose action is directed to the matter and to the form: else from the matter and the form there would not result something simply one. But the intellectual soul is the form of the human body, which is produced by the power of the semen. Therefore the intellectual soul also is Obj. 4: Further, man begets his like in species. But the human species is constituted by the rational soul. Therefore the rational soul is from the begetter.
Obj. 5: Further, it cannot be said that God concurs in sin. But if the rational soul be created by God, sometimes God concurs in the sin of adultery, since sometimes offspring is begotten of illicit intercourse. Therefore the rational soul is not created by God.
_On the contrary,_ It is written in De Eccl. Dogmat. xiv that "the rational soul is not engendered by coition."
_I answer that,_ It is impossible for an active power existing in matter to extend its action to the production of an immaterial effect. Now it is manifest that the intellectual principle in man transcends matter; for it has an operation in which the body takes no part whatever. It is therefore impossible for the seminal power to produce the intellectual principle.
Again, the seminal power acts by virtue of the soul of the begetter according as the soul of the begetter is the act of the body, making use of the body in its operation. Now the body has nothing whatever to do in the operation of the intellect. Therefore the power of the intellectual principle, as intellectual, cannot reach the semen.
Hence the Philosopher says (De Gener. Animal. ii, 3): "It follows that the intellect alone comes from without."
Again, since the intellectual soul has an operation independent of the body, it is subsistent, as proved above (Q. 75, A. 2): therefore to be and to be made are proper to it. Moreover, since it is an immaterial substance it cannot be caused through generation, but only through creation by God. Therefore to hold that the intellectual soul is caused by the begetter, is nothing else than to hold the soul to be non-subsistent and consequently to perish with the body. It is therefore heretical to say that the intellectual soul is transmitted with the semen.
Reply Obj. 1: In the passage quoted, the part is put instead of the whole, the soul for the whole man, by the figure of synecdoche.
Reply Obj. 2: Some say that the vital functions observed in the embryo are not from its soul, but from the soul of the mother; or from the formative power of the semen. Both of these explanations are false; for vital functions such as feeling, nourishment, and growth cannot be from an extrinsic principle. Consequently it must be said that the soul is in the embryo; the nutritive soul from the beginning, then the sensitive, lastly the intellectual soul.
Therefore some say that in addition to the vegetative soul which existed first, another, namely the sensitive, soul supervenes; and in addition to this, again another, namely the intellectual soul. Thus there would be in man three souls of which one would be in potentiality to another. This has been disproved above (Q. 76, A. 3).
Therefore others say that the same soul which was at first merely vegetative, afterwards through the action of the seminal power, becomes a sensitive soul; and finally this same soul becomes intellectual, not indeed through the active seminal power, but by the power of a higher agent, namely God enlightening (the soul) from without. For this reason the Philosopher says that the intellect comes from without. But this will not hold. First, because no substantial form is susceptible of more or less; but addition of greater perfection constitutes another species, just as the addition of unity constitutes another species of number. Now it is not possible for the same identical form to belong to different species.
Secondly, because it would follow that the generation of an animal would be a continuous movement, proceeding gradually from the imperfect to the perfect, as happens in alteration. Thirdly, because it would follow that the generation of a man or an animal is not generation simply, because the subject thereof would be a being in act. For if the vegetative soul is from the beginning in the matter of offspring, and is subsequently gradually brought to perfection; this will imply addition of further perfection without corruption of the preceding perfection. And this is contrary to the nature of generation properly so called. Fourthly, because either that which is caused by the action of God is something subsistent: and thus it must needs be essentially distinct from the pre-existing form, which was non-subsistent; and we shall then come back to the opinion of those who held the existence of several souls in the body--or else it is not subsistent, but a perfection of the pre-existing soul: and from this it follows of necessity that the intellectual soul perishes with the body, which cannot be admitted.
There is again another explanation, according to those who held that all men have but one intellect in common: but this has been disproved We must therefore say that since the generation of one thing is the corruption of another, it follows of necessity that both in men and in other animals, when a more perfect form supervenes the previous form is corrupted: yet so that the supervening form contains the perfection of the previous form, and something in addition. It is in this way that through many generations and corruptions we arrive at the ultimate substantial form, both in man and other animals. This indeed is apparent to the senses in animals generated from putrefaction. We conclude therefore that the intellectual soul is created by God at the end of human generation, and this soul is at the same time sensitive and nutritive, the pre-existing forms being corrupted.
Reply Obj. 3: This argument holds in the case of diverse agents not ordered to one another. But where there are many agents ordered to one another, nothing hinders the power of the higher agent from reaching to the ultimate form; while the powers of the inferior agents extend only to some disposition of matter: thus in the generation of an animal, the seminal power disposes the matter, but the power of the soul gives the form. Now it is manifest from what has been said above (Q. 105, A. 5; Q. 110, A. 1) that the whole of corporeal nature acts as the instrument of a spiritual power, especially of God. Therefore nothing hinders the formation of the body from being due to a corporeal power, while the intellectual soul is from God alone.
Reply Obj. 4: Man begets his like, forasmuch as by his seminal power the matter is disposed for the reception of a certain species of form.
Reply Obj. 5: In the action of the adulterer, what is of nature is good; in this God concurs. But what there is of inordinate lust is evil; in this God does not concur.
Whether Human Souls Were Created Together at the Beginning of the World?
Objection 1: It would seem that human souls were created together at the beginning of the world. For it is written (Gen. 2:2): "God rested Him from all His work which He had done." This would not be true if He created new souls every day. Therefore all souls were created at the same time.
Obj. 2: Further, spiritual substances before all others belong to the perfection of the universe. If therefore souls were created with the bodies, every day innumerable spiritual substances would be added to the perfection of the universe: consequently at the beginning the universe would have been imperfect. This is contrary to Gen. 2:2, where it is said that "God ended" all "His work."
Obj. 3: Further, the end of a thing corresponds to its beginning. But the intellectual soul remains, when the body perishes. Therefore it began to exist before the body.
_On the contrary,_ It is said (De Eccl. Dogmat. xiv, xviii) that "the soul is created together with the body."
_I answer that,_ Some have maintained that it is accidental to the intellectual soul to be united to the body, asserting that the soul is of the same nature as those spiritual substances which are not united to a body. These, therefore, stated that the souls of men were created together with the angels at the beginning. But this statement is false. Firstly, in the very principle on which it is based. For if it were accidental to the soul to be united to the body, it would follow that man who results from this union is a being by accident; or that the soul is a man, which is false, as proved above (Q. 75, A.
4). Moreover, that the human soul is not of the same nature as the angels, is proved from the different mode of understanding, as shown receiving from the senses, and turning to phantasms, as stated above (Q. 84, AA. 6, 7; Q. 85, A. 1). For this reason the soul needs to be united to the body, which is necessary to it for the operation of the sensitive part: whereas this cannot be said of an angel.
Secondly, this statement can be proved to be false in itself. For if it is natural to the soul to be united to the body, it is unnatural to it to be without a body, and as long as it is without a body it is deprived of its natural perfection. Now it was not fitting that God should begin His work with things imperfect and unnatural, for He did not make man without a hand or a foot, which are natural parts of a man. Much less, therefore, did He make the soul without a body.
But if someone say that it is not natural to the soul to be united to the body, he must give the reason why it is united to a body. And the reason must be either because the soul so willed, or for some other reason. If because the soul willed it--this seems incongruous. First, because it would be unreasonable of the soul to wish to be united to the body, if it did not need the body: for if it did need it, it would be natural for it to be united to it, since "nature does not fail in what is necessary." Secondly, because there would be no reason why, having been created from the beginning of the world, the soul should, after such a long time, come to wish to be united to the body. For a spiritual substance is above time, and superior to the heavenly revolutions. Thirdly, because it would seem that this body was united to this soul by chance: since for this union to take place two wills would have to concur--to wit, that of the incoming soul, and that of the begetter. If, however, this union be neither voluntary nor natural on the part of the soul, then it must be the result of some violent cause, and to the soul would have something of a penal and afflicting nature. This is in keeping with the opinion of Origen, who held that souls were embodied in punishment of sin. Since, therefore, all these opinions are unreasonable, we must simply confess that souls were not created before bodies, but are created at the same time as they are infused into them.
Reply Obj. 1: God is said to have rested on the seventh day, not from all work, since we read (John 5:17): "My Father worketh until now"; but from the creation of any new genera and species, which may not have already existed in the first works. For in this sense, the souls which are created now, existed already, as to the likeness of the species, in the first works, which included the creation of Adam's soul.
Reply Obj. 2: Something can be added every day to the perfection of the universe, as to the number of individuals, but not as to the number of species.
Reply Obj. 3: That the soul remains without the body is due to the corruption of the body, which was a result of sin. Consequently it was not fitting that God should make the soul without the body from the beginning: for as it is written (Wis. 1:13, 16): "God made not death...but the wicked with works and words have called it to them."
QUESTION 119 OF THE PROPAGATION OF MAN AS TO THE BODY (In Two Articles) We now consider the propagation of man, as to the body. Concerning this there are two points of inquiry: (1) Whether any part of the food is changed into true human nature?
(2) Whether the semen, which is the principle of human generation, is produced from the surplus food?
Whether Some Part of the Food Is Changed into True Human Nature?
Objection 1: It would seem that none of the food is changed into true human nature. For it is written (Matt. 15:17): "Whatsoever entereth into the mouth, goeth into the belly, and is cast out into the privy."
But what is cast out is not changed into the reality of human nature.
Therefore none of the food is changed into true human nature.
Obj. 2: Further, the Philosopher (De Gener. i, 5) distinguishes flesh belonging to the species from flesh belonging to "matter"; and says that the latter "comes and goes." Now what is formed from food comes and goes. Therefore what is produced from food is flesh belonging to matter, not to the species. But what belongs to true human nature belongs to the species. Therefore the food is not changed into true human nature.
Obj. 3: Further, the "radical humor" seems to belong to the reality of human nature; and if it be lost, it cannot be recovered, according to physicians. But it could be recovered if the food were changed into the humor. Therefore food is not changed into true human nature.
Obj. 4: Further, if the food were changed into true human nature, whatever is lost in man could be restored. But man's death is due only to the loss of something. Therefore man would be able by taking food to insure himself against death in perpetuity.
Obj. 5: Further, if the food is changed into true human nature, there is nothing in man which may not recede or be repaired: for what is generated in a man from his food can both recede and be repaired. If therefore a man lived long enough, it would follow that in the end nothing would be left in him of what belonged to him at the beginning. Consequently he would not be numerically the same man throughout his life; since for the thing to be numerically the same, identity of matter is necessary. But this is incongruous. Therefore the food is not changed into true human nature.
_On the contrary,_ Augustine says (De Vera Relig. xi): "The bodily food when corrupted, that is, having lost its form, is changed into the texture of the members." But the texture of the members belongs to true human nature. Therefore the food is changed into the reality of human nature.
_I answer that,_ According to the Philosopher (Metaph. ii), "The relation of a thing to truth is the same as its relation to being."
Therefore that belongs to the true nature of any thing which enters into the constitution of that nature. But nature can be considered in two ways: firstly, in general according to the species; secondly, as in the individual. And whereas the form and the common matter belong to a thing's true nature considered in general; individual signate matter, and the form individualized by that matter belong to the true nature considered in this particular individual. Thus a soul and body belong to the true human nature in general, but to the true human nature of Peter and Martin belong this soul and this body.
Now there are certain things whose form cannot exist but in one individual matter: thus the form of the sun cannot exist save in the matter in which it actually is. And in this sense some have said that the human form cannot exist but in a certain individual matter, which, they said, was given that form at the very beginning in the first man.
So that whatever may have been added to that which was derived by posterity from the first parent, does not belong to the truth of human nature, as not receiving in truth the form of human nature.
But, said they, that matter which, in the first man, was the subject of the human form, was multiplied in itself: and in this way the multitude of human bodies is derived from the body of the first man.
According to these, the food is not changed into true human nature; we take food, they stated, in order to help nature to resist the action of natural heat, and prevent the consumption of the "radical humor"; just as lead or tin is mixed with silver to prevent its being consumed by fire.
But this is unreasonable in many ways. Firstly, because it comes to the same that a form can be produced in another matter, or that it can cease to be in its proper matter; wherefore all things that can be generated are corruptible, and conversely. Now it is manifest that the human form can cease to exist in this (particular) matter which is its subject: else the human body would not be corruptible.
Consequently it can begin to exist in another matter, so that something else be changed into true human nature. Secondly, because in all beings whose entire matter is contained in one individual there is only one individual in the species: as is clearly the case with the sun, moon and such like. Thus there would only be one individual of the human species. Thirdly, because multiplication of matter cannot be understood otherwise than either in respect of quantity only, as in things which are rarefied, so that their matter increases in dimensions; or in respect of the substance itself of the matter. But as long as the substance alone of matter remains, it cannot be said to be multiplied; for multitude cannot consist in the addition of a thing to itself, since of necessity it can only result from division. Therefore some other substance must be added to matter, either by creation, or by something else being changed into it. Consequently no matter can be multiplied save either by rarefaction as when air is made from water; or by the change of some other things, as fire is multiplied by the addition of wood; or lastly by creation. Now it is manifest that the multiplication of matter in the human body does not occur by rarefaction: for thus the body of a man of perfect age would be more imperfect than the body of a child. Nor does it occur by creation of fresh matter: for, according to Gregory (Moral. xxxii): "All things were created together as to the substance of matter, but not as to the specific form." Consequently the multiplication of the human body can only be the result of the food being changed into the true human nature.
Fourthly, because, since man does not differ from animals and plants in regard to the vegetative soul, it would follow that the bodies of animals and plants do not increase through a change of nourishment into the body so nourished, but through some kind of multiplication.
Which multiplication cannot be natural: since the matter cannot naturally extend beyond a certain fixed quantity; nor again does anything increase naturally, save either by rarefaction or the change of something else into it. Consequently the whole process of generation and nourishment, which are called "natural forces," would be miraculous. Which is altogether inadmissible.
Wherefore others have said that the human form can indeed begin to exist in some other matter, if we consider the human nature in general: but not if we consider it as in this individual. For in the individual the form remains confined to a certain determinate matter, on which it is first imprinted at the generation of that individual, so that it never leaves that matter until the ultimate dissolution of the individual. And this matter, say they, principally belongs to the true human nature. But since this matter does not suffice for the requisite quantity, some other matter must be added, through the change of food into the substance of the individual partaking thereof, in such a quantity as suffices for the increase required.
And this matter, they state, belongs secondarily to the true human nature: because it is not required for the primary existence of the individual, but for the quantity due to him. And if anything further is produced from the food, this does not belong to true human nature, properly speaking. However, this also is inadmissible. First, because this opinion judges of living bodies as of inanimate bodies; in which, although there be a power of generating their like in species, there is not the power of generating their like in the individual; which power in living bodies is the nutritive power. Nothing, therefore, would be added to living bodies by their nutritive power, if their food were not changed into their true nature. Secondly, because the active seminal power is a certain impression derived from the soul of the begetter, as stated above (Q. 118, A. 1). Hence it cannot have a greater power in acting, than the soul from which it is derived. If, therefore, by the seminal power a certain matter truly assumes the form of human nature, much more can the soul, by the nutritive power, imprint the true form of human nature on the food which is assimilated. Thirdly, because food is needed not only for growth, else at the term of growth, food would be needful no longer; but also to renew that which is lost by the action of natural heat.
But there would be no renewal, unless what is formed from the food, took the place of what is lost. Wherefore just as that which was there previously belonged to true human nature, so also does that which is formed from the food.
Therefore, according to others, it must be said that the food is really changed into the true human nature by reason of its assuming the specific form of flesh, bones and such like parts. This is what the Philosopher says (De Anima ii, 4): "Food nourishes inasmuch as it is potentially flesh."
Reply Obj. 1: Our Lord does not say that the "whole" of what enters into the mouth, but "all"--because something from every kind of food is cast out into the privy. It may also be said that whatever is generated from food, can be dissolved by natural heat, and be cast aside through the pores, as Jerome expounds the passage.
Reply Obj. 2: By flesh belonging to the species, some have understood that which first receives the human species, which is derived from the begetter: this, they say, lasts as long as the individual does.
By flesh belonging to the matter these understand what is generated from food: and this, they say, does not always remain, but as it comes so it goes. But this is contrary to the mind of Aristotle. For he says there, that "just as in things which have their species in matter"--for instance, wood or stone--"so in flesh, there is something belonging to the species, and something belonging to matter." Now it is clear that this distinction has no place in inanimate things, which are not generated seminally, or nourished.
Again, since what is generated from food is united to, by mixing with, the body so nourished, just as water is mixed with wine, as the Philosopher says there by way of example: that which is added, and that to which it is added, cannot be different natures, since they are already made one by being mixed together. Therefore there is no reason for saying that one is destroyed by natural heat, while the other remains.
It must therefore be said that this distinction of the Philosopher is not of different kinds of flesh, but of the same flesh considered from different points of view. For if we consider the flesh according to the species, that is, according to that which is formed therein, thus it remains always: because the nature of flesh always remains together with its natural disposition. But if we consider flesh according to matter, then it does not remain, but is gradually destroyed and renewed: thus in the fire of a furnace, the form of fire remains, but the matter is gradually consumed, and other matter is substituted in its place.
Reply Obj. 3: The "radical humor" is said to comprise whatever the virtue of the species is founded on. If this be taken away it cannot be renewed; as when a man's hand or foot is amputated. But the "nutritive humor" is that which has not yet received perfectly the specific nature, but is on the way thereto; such is the blood, and the like. Wherefore if such be taken away, the virtue of the species remains in its root, which is not destroyed.
Reply Obj. 4: Every virtue of a passible body is weakened by continuous action, because such agents are also patient. Therefore the transforming virtue is strong at first so as to be able to transform not only enough for the renewal of what is lost, but also for growth. Later on it can only transform enough for the renewal of what is lost, and then growth ceases. At last it cannot even do this; and then begins decline. In fine, when this virtue fails altogether, the animal dies. Thus the virtue of wine that transforms the water added to it, is weakened by further additions of water, so as to become at length watery, as the Philosopher says by way of example (De Gener. i, 5).
Reply Obj. 5: As the Philosopher says (De Gener. i, 5), when a certain matter is directly transformed into fire, then fire is said to be generated anew: but when matter is transformed into a fire already existing, then fire is said to be fed. Wherefore if the entire matter together loses the form of fire, and another matter transformed into fire, there will be another distinct fire. But if, while one piece of wood is burning, other wood is laid on, and so on until the first piece is entirely consumed, the same identical fire will remain all the time: because that which is added passes into what pre-existed. It is the same with living bodies, in which by means of nourishment that is renewed which was consumed by natural heat.
Whether the Semen Is Produced from Surplus Food?
Objection 1: It would seem that the semen is not produced from the surplus food, but from the substance of the begetter. For Damascene says (De Fide Orth. i, 8) that "generation is a work of nature, producing, from the substance of the begetter, that which is begotten." But that which is generated is produced from the semen.
Therefore the semen is produced from the substance of the begetter.
Obj. 2: Further, the son is like his father, in respect of that which he receives from him. But if the semen from which something is generated, is produced from the surplus food, a man would receive