Summa Th. III EN Qu.31 a.5
Objection: 1. It would seem that the flesh of Christ was not conceived of the Virgin's purest blood: For it is said in the collect (Feast of the Annunciation) that God "willed that His Word should take flesh from a Virgin." But flesh differs from blood. Therefore Christ's body was not taken from the Virgin's blood.
2. Further, as the woman was miraculously formed from the man, so Christ's body was formed miraculously from the Virgin. But the woman is not said to have been formed from the man's blood, but rather from his flesh and bones, according to Gn 2,23: "This now is bone of my bones, and flesh of my flesh." It seems therefore that neither should Christ's body have been formed from the Virgin's blood, but from her flesh and bones.
3. Further, Christ's body was of the same species as other men's bodies. But other men's bodies are not formed from the purest blood but from the semen and the menstrual blood. Therefore it seems that neither was Christ's body conceived of the purest blood of the Virgin.
On the contrary Damascene says (De Fide Orth. iii) that "the Son of God, from the Virgin's purest blood, formed Himself flesh, animated with a rational soul."
I answer that As stated above (Article ), in Christ's conception His being born of a woman was in accordance with the laws of nature, but that He was born of a virgin was above the laws of nature. Now, such is the law of nature that in the generation of an animal the female supplies the matter, while the male is the active principle of generation; as the Philosopher proves (De Gener. Animal. i). But a woman who conceives of a man is not a virgin. And consequently it belongs to the supernatural mode of Christ's generation, that the active principle of generation was the supernatural power of God: but it belongs to the natural mode of His generation, that the matter from which His body was conceived is similar to the matter which other women supply for the conception of their offspring. Now, this matter, according to the Philosopher (De Gener. Animal.), is the woman's blood, not any of her blood, but brought to a more perfect stage of secretion by the mother's generative power, so as to be apt for conception. And therefore of such matter was Christ's body conceived.
Reply to Objection: 1. Since the Blessed Virgin was of the same nature as other women, it follows that she had flesh and bones of the same nature as theirs. Now, flesh and bones in other women are actual parts of the body, the integrity of which results therefrom: and consequently they cannot be taken from the body without its being corrupted or diminished. But as Christ came to heal what was corrupt, it was not fitting that He should bring corruption or diminution to the integrity of His Mother. Therefore it was becoming that Christ's body should be formed not from the flesh or bones of the Virgin, but from her blood, which as yet is not actually a part, but is potentially the whole, as stated in De Gener. Animal. i. Hence He is said to have taken flesh from the Virgin, not that the matter from which His body was formed was actual flesh, but blood, which is flesh potentially.
2. As stated in the FP, Question , Article , ad 2, Adam, through being established as a kind of principle of human nature, had in his body a certain proportion of flesh and bone, which belonged to him, not as an integral part of his personality, but in regard to his state as a principle of human nature. And from this was the woman formed, without detriment to the man. But in the Virgin's body there was nothing of this sort, from which Christ's body could be formed without detriment to His Mother's body.
3. Woman's semen is not apt for generation, but is something imperfect in the seminal order, which, on account of the imperfection of the female power, it has not been possible to bring to complete seminal perfection. Consequently this semen is not the necessary matter of conception; as the Philosopher says (De Gener. Animal. i): wherefore there was none such in Christ's conception: all the more since, though it is imperfect in the seminal order, a certain concupiscence accompanies its emission, as also that of the male semen: whereas in that virginal conception there could be no concupiscence. Wherefore Damascene says (De Fide Orth. iii) that Christ's body was not conceived "seminally." But the menstrual blood, the flow of which is subject to monthly periods, has a certain natural impurity of corruption: like other superfluities, which nature does not heed, and therefore expels. Of such menstrual blood infected with corruption and repudiated by nature, the conception is not formed; but from a certain secretion of the pure blood which by a process of elimination is prepared for conception, being, as it were, more pure and more perfect than the rest of the blood. Nevertheless, it is tainted with the impurity of lust in the conception of other men: inasmuch as by sexual intercourse this blood is drawn to a place apt for conception. This, however, did not take place in Christ's conception: because this blood was brought together in the Virgin's womb and fashioned into a child by the operation of the Holy Ghost. Therefore is Christ's body said to be "formed of the most chaste and purest blood of the Virgin."
Objection: 1. It would seem that Christ's body was in Adam and the patriarchs as to something signate. For Augustine says (Gn ad lit. x) that the flesh of Christ was in Adam and Abraham "by way of a bodily substance." But bodily substance is something signate. Therefore Christ's flesh was in Adam, Abraham, and the other patriarchs, according to something signate.
2. Further, it is said (Rm 1,3) that Christ "was made . . . of the seed of David according to the flesh." But the seed of David was something signate in him. Therefore Christ was in David, according to something signate, and for the same reason in the other patriarchs.
3. Further, the human race is Christ's kindred, inasmuch as He took flesh therefrom. But if that flesh were not something signate in Adam, the human race, which is descended from Adam, would seem to have no kindred with Christ: but rather with those other things from which the matter of His flesh was taken. Therefore it seems that Christ's flesh was in Adam and the other patriarchs according to something signate.
On the contrary Augustine says (Gn ad lit. x) that in whatever way Christ was in Adam and Abraham, other men were there also; but not conversely. But other men were not in Adam and Abraham by way of some signate matter, but only according to origin, as stated in the FP, Question  , Article , Article , ad 4. Therefore neither was Christ in Adam and Abraham according to something signate; and, for the same reason, neither was He in the other patriarchs.
I answer that As stated above (Article , ad 1), the matter of Christ's body was not the flesh and bones of the Blessed Virgin, nor anything that was actually a part of her body, but her blood which was her flesh potentially. Now, whatever was in the Blessed Virgin, as received from her parents, was actually a part of her body. Consequently that which the Blessed Virgin received from her parents was not the matter of Christ's body. Therefore we must say that Christ's body was not in Adam and the other patriarchs according to something signate, in the sense that some part of Adam's or of anyone else's body could be singled out and designated as the very matter from which Christ's body was to be formed: but it was there according to origin, just as was the flesh of other men. For Christ's body is related to Adam and the other patriarchs through the medium of His Mother's body. Consequently Christ's body was in the patriarchs, in no other way than was His Mother's body, which was not in the patriarchs according to signate matter: as neither were the bodies of other men, as stated in the FP, Question , Article , Article , ad 4.
Reply to Objection: 1. The expression "Christ was in Adam according to bodily substance," does not mean that Christ's body was a bodily substance in Adam: but that the bodily substance of Christ's body, i.e. the matter which He took from the Virgin, was in Adam as in its active principle, but not as in its material principle: in other words, by the generative power of Adam and his descendants down to the Blessed Virgin, this matter was prepared for Christ's conception. But this matter was not fashioned into Christ's body by the seminal power derived from Adam. Therefore Christ is said to have been in Adam by way of origin, according to bodily substance: but not according to seminal virtue.
2. Although Christ's body was not in Adam and the other patriarchs, according to seminal virtue, yet the Blessed Virgin's body was thus in them, through her being conceived from the seed of a man. For this reason, through the medium of the Blessed Virgin, Christ is said to be of the seed of David, according to the flesh, by way of origin.
3. Christ and the human race are kindred, through the likeness of species. Now, specific likeness results not from remote but from proximate matter, and from the active principle which begets its like in species. Thus, then, the kinship of Christ and the human race is sufficiently preserved by His body being formed from the Virgin's blood, derived in its origin from Adam and the other patriarchs. Nor is this kinship affected by the matter whence this blood is taken, as neither is it in the generation of other men, as stated in the FP, Question , Article , ad 3.
Objection: 1. It would seem that Christ's flesh was not infected by sin in the patriarchs. For it is written (Sg 7,25) that "no defiled thing cometh into" Divine Wisdom. But Christ is the Wisdom of God according to 1Co 1,24. Therefore Christ's flesh was never defiled by sin.
2. Further, Damascene says (De Fide Orth. iii) that Christ "assumed the first-fruits of our nature." But in the primitive state human flesh was not infected by sin. Therefore Christ's flesh was not infected either in Adam or in the other patriarchs.
3. Further, Augustine says (Gn ad lit. x) that "human nature ever had, together with the wound, the balm with which to heal it." But that which is infected cannot heal a wound; rather does it need to be healed itself. Therefore in human nature there was ever something preserved from infection, from which afterwards Christ's body was formed.
On the contrary Christ's body is not related to Adam and the other patriarchs, save through the medium of the Blessed Virgin's body, of whom He took flesh. But the body of the Blessed Virgin was wholly conceived in original sin, as stated above (Question , Article , ad 1), and thus, as far as it was in the patriarchs, it was subject to sin. Therefore the flesh of Christ, as far as it was in the patriarchs, was subject to sin.
I answer that When we say that Christ or His flesh was in Adam and the other patriarchs, we compare Him, or His flesh, to Adam and the other patriarchs. Now, it is manifest that the condition of the patriarchs differed from that of Christ: for the patriarchs were subject to sin, whereas Christ was absolutely free from sin. Consequently a twofold error may occur on this point. First, by attributing to Christ, or to His flesh, that condition which was in the patriarchs; by saying, for instance, that Christ sinned in Adam, since after some fashion He was in him. But this is false; because Christ was not in Adam in such a way that Adam's sin belonged to Christ: forasmuch as He is not descended from him according to the law of concupiscence, or according to seminal virtue; as stated above (Article , ad 3, Article , ad 1; Question , Article , ad 2).Secondly, error may occur by attributing the condition of Christ or of His flesh to that which was actually in the patriarchs: by saying, for instance, that, because Christ's flesh, as existing in Christ, was not subject to sin, therefore in Adam also and in the patriarchs there was some part of his body that was not subject to sin, and from which afterwards Christ's body was formed; as some indeed held. For this is quite impossible. First, because Christ's flesh was not in Adam and in the other patriarchs, according to something signate, distinguishable from the rest of his flesh, as pure from impure; as already stated (Article ). Secondly, because since human flesh is infected by sin, through being conceived in lust, just as the entire flesh of a man is conceived through lust, so also is it entirely defiled by sin. Consequently we must say that the entire flesh of the patriarchs was subjected to sin, nor was there anything in them that was free from sin, and from which afterwards Christ's body could be formed.
Reply to Objection: 1. Christ did not assume the flesh of the human race subject to sin, but cleansed from all infection of sin. Thus it is that "no defiled thing cometh into the Wisdom of God."
2. Christ is said to have assumed the first-fruits of our nature, as to the likeness of condition; forasmuch as He assumed flesh not infected by sin, like unto the flesh of man before sin. But this is not to be understood to imply a continuation of that primitive purity, as though the flesh of innocent man was preserved in its freedom from sin until the formation of Christ's body.
3. Before Christ, there was actually in human nature a wound, i.e. the infection of original sin. But the balm to heal the wound was not there actually, but only by a certain virtue of origin, forasmuch as from those patriarchs the flesh of Christ was to be propagated.
Objection: 1. It would seem that Christ "paid tithes" in Abraham's loins. For the Apostle says (He 7,6-9) that Levi, the great-grandson of Abraham, "paid tithes in Abraham," because, when the latter paid tithes to Melchisedech, "he was yet in his loins." In like manner Christ was in Abraham's loins when the latter paid tithes. Therefore Christ Himself also paid tithes in Abraham.
2. Further, Christ is of the seed of Abraham according to the flesh which He received from His Mother. But His Mother paid tithes in Abraham. Therefore for a like reason did Christ.
3. Further, "in Abraham tithe was levied on that which needed healing," as Augustine says (Gn ad lit. x). But all flesh subject to sin needed healing. Since therefore Christ's flesh was the subject of sin, as stated above (Article ), it seems that Christ's flesh paid tithes in Abraham.
4. Further, this does not seem to be at all derogatory to Christ's dignity. For the fact that the father of a bishop pays tithes to a priest does not hinder his son, the bishop, from being of higher rank than an ordinary priest. Consequently, although we may say that Christ paid tithes when Abraham paid them to Melchisedech, it does not follow that Christ was not greater than Melchisedech.
On the contrary Augustine says (Gn ad lit. x) that "Christ did not pay tithes there," i.e. in Abraham, "for His flesh derived from him, not the heat of the wound, but the matter of the antidote."
I answer that It behooves us to say that the sense of the passage quoted from the Apostle is that Christ did not pay tithes in Abraham. For the Apostle proves that the priesthood according to the order of Melchisedech is greater than the Levitical priesthood, from the fact that Abraham paid tithes to Melchisedech, while Levi, from whom the legal priesthood was derived, was yet in his loins. Now, if Christ had also paid tithes in Abraham, His priesthood would not have been according to the order of Melchisedech, but of a lower order. Consequently we must say that Christ did not pay tithes in Abraham's loins, as Levi did.For since he who pays a tithe keeps nine parts to himself, and surrenders the tenth to another, inasmuch as the number ten is the sign of perfection, as being, in a sort, the terminus of all numbers which mount from one to ten, it follows that he who pays a tithe bears witness to his own imperfection and to the perfection of another. Now, to sin is due the imperfection of the human race, which needs to be perfected by Him who cleanses from sin. But to heal from sin belongs to Christ alone, for He is the "Lamb that taketh away the sin of the world" (Jn 1,29), whose figure was Melchisedech, as the Apostle proves (He 7). Therefore by giving tithes to Melchisedech, Abraham foreshadowed that he, as being conceived in sin, and all who were to be his descendants in contracting original sin, needed that healing which is through Christ. And Isaac, Jacob, and Levi, and all the others were in Abraham in such a way so as to be descended from him, not only as to bodily substance, but also as to seminal virtue, by which original sin is transmitted. Consequently, they all paid tithes in Abraham, i.e. foreshadowed as needing to be healed by Christ. And Christ alone was in Abraham in such a manner as to descend from him, not by seminal virtue, but according to bodily substance. Therefore He was not in Abraham so as to need to be healed, but rather "as the balm with which the wound was to be healed." Therefore He did not pay tithes in Abraham's loins.
Reply to Objection: 1. Thus the answer to the first objection is made manifest.
2. Because the Blessed Virgin was conceived in original sin, she was in Abraham as needing to be healed. Therefore she paid tithes in him, as descending from him according to seminal virtue. But this is not true of Christ's body, as stated above.
3. Christ's flesh is said to have been subject to sin, according as it was in the patriarchs, by reason of the condition in which it was in His forefathers, who paid the tithes: but not by reason of its condition as actually in Christ, who did not pay the tithes.
4. The levitical priesthood was handed down through carnal origin: wherefore it was not less in Abraham than in Levi. Consequently, since Abraham paid tithes to Melchisedech as to one greater than he, it follows that the priesthood of Melchisedech, inasmuch as he was a figure of Christ, was greater than that of Levi. But the priesthood of Christ does not result from carnal origin, but from spiritual grace. Therefore it is possible that a father pay tithes to a priest, as the less to the greater, and yet his son, if he be a bishop, is greater than that priest, not through carnal origin, but through the spiritual grace which he has received from Christ.
We shall now consider the active principle in Christ's conception: concerning which there are four points of inquiry:
(1) Whether the Holy Ghost was the active principle of Christ's conception?
(2) Whether it can be said that Christ was conceived of the Holy Ghost?
(3) Whether it can be said that the Holy Ghost is Christ's father according to the flesh?
(4) Whether the Blessed Virgin cooperated actively in Christ's conception?
Objection: 1. It would seem that the accomplishment of Christ's conception should not be attributed to the Holy Ghost, because. as Augustine says (De Trin. i), "The works of the Trinity are indivisible, just as the Essence of the Trinity is indivisible." But the accomplishment of Christ's conception was the work of God. Therefore it seems that it should not be attributed to the Holy Ghost any more than to the Father or the Son.
2. Further, the Apostle says (Ga 4,4): "When the fulness of time was come, God sent His Son, made of a woman"; which words Augustine expounds by saying (De Trin. iv): "Sent, in so far as made of a woman." But the sending of the Son is especially attributed to the Father, as stated in the FP, Question , Article . Therefore His conception also, by reason of which He was "made of a woman," should be attributed principally to the Father.
3. Further, it is written (Pr 9,1): "Wisdom hath built herself a house." Now, Christ is Himself the Wisdom of God; according to 1Co 1,24: "Christ the Power of God and the Wisdom of God." And the house of this Wisdom is Christ's body, which is also called His temple, according to Jn 2,21: "But He spoke of the temple of His body." Therefore it seems that the accomplishment of Christ's conception should be attributed principally to the Son, and not, therefore, to the Holy Ghost.
On the contrary It is written (Lc 1,35): "The Holy Ghost shall come upon Thee."
I answer that The whole Trinity effected the conception of Christ's body: nevertheless, this is attributed to the Holy Ghost, for three reasons. First, because this is befitting to the cause of the Incarnation, considered on the part of God. For the Holy Ghost is the love of Father and Son, as stated in the FP, Question , Article . Now, that the Son of God took to Himself flesh from the Virgin's womb was due to the exceeding love of God: wherefore it is said (Jn 3,16): "God so loved the world as to give His only-begotten Son."Secondly, this is befitting to the cause of the Incarnation, on the part of the nature assumed. Because we are thus given to understand that human nature was assumed by the Son of God into the unity of Person, not by reason of its merits, but through grace alone; which is attributed to the Holy Ghost, according to 1Co 12,4: "There are diversities of graces, but the same Spirit." Wherefore Augustine says (Enchiridion xl): "The manner in which Christ was born of the Holy Ghost . . . suggests to us the grace of God, whereby man, without any merits going before, in the very beginning of his nature when he began to exist was joined to God the Word, into so great unity of Person, that He Himself should be the Son of God."Thirdly, because this is befitting the term of the Incarnation. For the term of the Incarnation was that that man, who was being conceived, should be the Holy one and the Son of God. Now, both of these are attributed to the Holy Ghost. For by Him men are made to be sons of God, according to Ga 4,6: "Because you are sons, God hath sent the Spirit of His Son into your [Vulg.: 'our'] hearts, crying: Abba, Father." Again, He is the "Spirit of sanctification," according to Rm 1,4. Therefore, just as other men are sanctified spiritually by the Holy Ghost; so as to be the adopted sons of God, so was Christ conceived in sanctity by the Holy Ghost, so as to be the natural Son of God. Hence, according to a gloss on Rm 1,4, the words, "Who was predestinated the Son of God, in power," are explained by what immediately follows: "According to the Spirit of sanctification, i.e. through being conceived of the Holy Ghost." And the Angel of the Annunciation himself, after saying, "The Holy Ghost shall come upon thee," draws the conclusion: "Therefore also the Holy which shall be born of thee shall be called the Son of God."
Reply to Objection: 1. The work of the conception is indeed common to the whole Trinity; yet in some way it is attributed to each of the Persons. For to the Father is attributed authority in regard to the Person of the Son, who by this conception took to Himself (human nature). The taking itself (of human nature) is attributed to the Son: but the formation of the body taken by the Son is attributed to the Holy Ghost. For the Holy Ghost is the Spirit of the Son, according to Ga 4,6: "God sent the Spirit of His Son." For just as the power of the soul which is in the semen, through the spirit enclosed therein, fashions the body in the generation of other men, so the Power of God, which is the Son Himself, according to 1Co 1,24: "Christ, the Power of God," through the Holy Ghost formed the body which He assumed. This is also shown by the words of the angel: "The Holy Ghost shall come upon thee," as it were, in order to prepare and fashion the matter of Christ's body; "and the Power of the Most High," i.e. Christ, "shall overshadow thee---that is to say, the incorporeal Light of the Godhead shall in thee take the corporeal substance of human nature: for a shadow is formed by light and body," as Gregory says (Moral. xviii). The "Most High" is the Father, whose Power is the Son.
2. The mission refers to the Person assuming, who is sent by the Father; but the conception refers to the body assumed, which is formed by the operation of the Holy Ghost. And therefore, though mission and conception are in the same subject; since they differ in our consideration of them, mission is attributed to the Father, but the accomplishment of the conception to the Holy Ghost; whereas the assumption of flesh is attributed to the Son.
3. As Augustine says (Questions. Vet. et Nov. Test., qu. 52): "This may be understood in two ways. For, first, Christ's house is the Church, which He built with His blood. Secondly, His body may be called His house, just as it is called His temple . . . and what is done by the Holy Ghost is done by the Son of God, because Theirs is one Nature and one Will."
Objection: 1. It would seem that we should not say that Christ was conceived of [de] the Holy Ghost. Because on Rm 11,36: "For of Him [ex ipso] and by Him, and in Him, are all things," the gloss of Augustine says: "Notice that he does not say, 'of Him' [de ipso], but 'of Him' [ex ipso]. For of Him [ex ipso], are heaven and earth, since He made them: but not of Him [de ipso], since they are not made of His substance." But the Holy Ghost did not form Christ's body of [de] His own substance. Therefore we should not say that Christ was conceived of [de] the Holy Ghost.
2. Further, the active principle of [de] which something is conceived is as the seed in generation. But the Holy Ghost did not take the place of seed in Christ's conception. For Jerome says (Expos. Cathol. Fidei) [*Written by Pelagius]: "We do not say, as some wicked wretches hold, that the Holy Ghost took the place of seed: but we say that Christ's body was wrought," i.e. formed, "by the power and might of the Creator." Therefore we should not say that Christ's body was conceived of [de] the Holy Ghost.
3. Further, no one thing is made of two, except they be in some way mingled. But Christ's body was formed of [de] the Virgin Mary. If therefore we say that Christ was conceived of [de] the Holy Ghost, it seems that a mingling took place of the Holy Ghost with the matter supplied by the Virgin: and this is clearly false. Therefore we should not say that Christ was conceived of [de] the Holy Ghost.
On the contrary It is written (Mt 1,18): "Before they came together, she was found with child, of [de] the Holy Ghost."
I answer that Conception is not attributed to Christ's body alone, but also to Christ Himself by reason of His body. Now, in the Holy Ghost we may observe a twofold habitude to Christ. For to the Son of God Himself, who is said to have been conceived, He has a habitude of consubstantiality: while to His body He has the habitude of efficient cause. And this preposition of [de] signifies both habitudes: thus we say that a certain man is "of [de] his father." And therefore we can fittingly say that Christ was conceived of the Holy Ghost in such a way that the efficiency of the Holy Ghost be referred to the body assumed, and the consubstantiality to the Person assuming.
Reply to Objection: 1. Christ's body, through not being consubstantial with the Holy Ghost, cannot properly be said to be conceived "of" [de] the Holy Ghost, but rather "from [ex] the Holy Ghost," as Ambrose says (De Spir. Sanct. ii.): "What is from someone is either from his substance or from his power: from his substance, as the Son who is from the Father; from his power, as all things are from God, just as Mary conceived from the Holy Ghost."
2. It seems that on this point there is a difference of opinion between Jerome and certain other Doctors, who assert that the Holy Ghost took the place of seed in this conception. For Chrysostom says (Hom. i in Matth. [*Opus Imperf., among the supposititious writings]): "When God's Only-Begotten was about to enter into the Virgin, the Holy Ghost preceded Him; that by the previous entrance of the Holy Ghost, Christ might be born unto sanctification according to His body, the Godhead entering instead of the seed." And Damascene says (De Fide Orth. iii): "God's wisdom and power overshadowed her, like unto a Divine seed."But these expressions are easily explained. Because Chrysostom and Damascene compare the Holy Ghost, or also the Son, who is the Power of the Most High, to seed, by reason of the active power therein; while Jerome denies that the Holy Ghost took the place of seed, considered as a corporeal substance which is transformed in conception.
3. As Augustine says (Enchiridion xl), Christ is said to be conceived or born of the Holy Ghost in one sense; of the Virgin Mary in another---of the Virgin Mary materially; of the Holy Ghost efficiently. Therefore there was no mingling here.
Objection: 1. It would seem that the Holy Ghost should be called Christ's father in respect of His humanity. Because, according to the Philosopher (De Gener. Animal. i): "The Father is the active principle in generation, the Mother supplies the matter." But the Blessed Virgin is called Christ's Mother, by reason of the matter which she supplied in His conception. Therefore it seems that the Holy Ghost can be called His father, through being the active principle in His conception.
2. Further, as the minds of other holy men are fashioned by the Holy Ghost, so also was Christ's body fashioned by the Holy Ghost. But other holy men, on account of the aforesaid fashioning, are called the children of the whole Trinity, and consequently of the Holy Ghost. Therefore it seems that Christ should be called the Son of the Holy Ghost, forasmuch as His body was fashioned by the Holy Ghost.
3. Further, God is called our Father by reason of His having made us, according to Dt 32,6: "Is not He thy Father, that hath possessed thee, and made thee and created thee?" But the Holy Ghost made Christ's body, as stated above (Articles ,2). Therefore the Holy Ghost should be called Christ's Father in respect of the body fashioned by Him.
On the contrary Augustine says (Enchiridion xl): "Christ was born of the Holy Ghost not as a Son, and of the Virgin Mary as a Son."
I answer that The words "fatherhood," "motherhood," and "sonship," result from generation; yet not from any generation, but from that of living things, especially animals. For we do not say that fire generated is the son of the fire generating it, except, perhaps, metaphorically; we speak thus only of animals in whom generation is more perfect. Nevertheless, the word "son" is not applied to everything generated in animals, but only to that which is generated into likeness of the generator. Wherefore, as Augustine says (Enchiridion xxxix), we do not say that a hair which is generated in a man is his son; nor do we say that a man who is born is the son of the seed; for neither is the hair like the man nor is the man born like the seed, but like the man who begot him. And if the likeness be perfect, the sonship is perfect, whether in God or in man. But if the likeness be imperfect, the sonship is imperfect. Thus in man there is a certain imperfect likeness to God, both as regards his being created to God's image and as regards His being created unto the likeness of grace. Therefore in both ways man can be called His son, both because he is created to His image and because he is likened to Him by grace. Now, it must be observed that what is said in its perfect sense of a thing should not be said thereof in its imperfect sense: thus, because Socrates is said to be naturally a man, in the proper sense of "man," never is he called man in the sense in which the portrait of a man is called a man, although, perhaps, he may resemble another man. Now, Christ is the Son of God in the perfect sense of sonship. Wherefore, although in His human nature He was created and justified, He ought not to be called the Son of God, either in respect of His being created or of His being justified, but only in respect of His eternal generation, by reason of which He is the Son of the Father alone. Therefore nowise should Christ be called the Son of the Holy Ghost, nor even of the whole Trinity.
Reply to Objection: 1. Christ was conceived of the Virgin Mary, who supplied the matter of His conception unto likeness of species. For this reason He is called her Son. But as man He was conceived of the Holy Ghost as the active principle of His conception, but not unto likeness of species, as a man is born of his father. Therefore Christ is not called the Son of the Holy Ghost.
2. Men who are fashioned spiritually by the Holy Ghost cannot be called sons of God in the perfect sense of sonship. And therefore they are called sons of God in respect of imperfect sonship, which is by reason of the likeness of grace, which flows from the whole Trinity.But with Christ it is different, as stated above.
3. The same reply avails for the Third Objection.
Summa Th. III EN Qu.31 a.5