Summa Theologica, by St. Thomas Aquinas, [1947], at sacred-texts.com
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.
Objection 2: Further, the Apostle says (Gal. 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, Q[43], A[8]. Therefore His conception also, by reason of which He was "made of a woman," should be attributed principally to the Father.
Objection 3: Further, it is written (Prov. 9:1): "Wisdom hath built herself a house." Now, Christ is Himself the Wisdom of God; according to 1 Cor. 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 (Lk. 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, Q[37], A[1]. 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 1 Cor. 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 Gal. 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 Rom. 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 Rom. 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 Gal. 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 1 Cor. 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.
Reply to Objection 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.
Reply to Objection 3: As Augustine says (QQ. 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 Rom. 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.
Objection 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.
Objection 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 (Mat. 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."
Reply to Objection 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.
Reply to Objection 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.
Objection 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.
Objection 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 (AA[1],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.
Reply to Objection 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.
The same reply avails for the Third Objection.
Objection 1: It would seem that the Blessed Virgin cooperated actively in the conception of Christ's body. For Damascene says (De Fide Orth. iii) that "the Holy Ghost came upon the Virgin, purifying her, and bestowing on her the power to receive and to bring forth the Word of God." But she had from nature the passive power of generation, like any other woman. Therefore He bestowed on her an active power of generation. And thus she cooperated actively in Christ's conception.
Objection 2: Further, all the powers of the vegetative soul are active, as the Commentator says (De Anima ii). But the generative power, in both man and woman, belongs to the vegetative soul. Therefore, both in man and woman, it cooperates actively in the conception of the child.
Objection 3: Further, in the conception of a child the woman supplies the matter from which the child's body is naturally formed. But nature is an intrinsic principle of movement. Therefore it seems that in the very matter supplied by the Blessed Virgin there was an active principle.
On the contrary, The active principle in generation is called the "seminal virtue." But, as Augustine says (Gen. ad lit. x), Christ's body "was taken from the Virgin, only as to corporeal matter, by the Divine power of conception and formation, but not by any human seminal virtue." Therefore the Blessed Virgin did not cooperate actively in, the conception of Christ's body.
I answer that, Some say that the Blessed Virgin cooperated actively in Christ's conception, both by natural and by a supernatural power. By natural power, because they hold that in all natural matter there is an active principle. otherwise they believe that there would be no such thing as natural transformation. But in this they are deceived. Because a transformation is said to be natural by reason not only of an active but also of a passive intrinsic principle: for the Philosopher says expressly (Phys. viii) that in heavy and light things there is a passive, and not an active, principle of natural movement. Nor is it possible for matter to be active in its own formation, since it is not in act. Nor, again, is it possible for anything to put itself in motion except it be divided into two parts, one being the mover, the other being moved: which happens in animate things only, as is proved Phys. viii.
By a supernatural power, because they say that the mother requires not only to supply the matter, which is the menstrual blood, but also the semen, which, being mingled with that of the male, has an active power in generation. And since in the Blessed Virgin there was no resolution of semen, by reason of her inviolate virginity, they say that the Holy Ghost supernaturally bestowed on her an active power in the conception of Christ's body, which power other mothers have by reason of the semen resolved. But this cannot stand, because, since "each thing is on account of its operation" (De Coel. ii), nature would not, for the purpose of the act of generation, distinguish the male and female sexes, unless the action of the male were distinct from that of the female. Now, in generation there are two distinct operations---that of the agent and that of the patient. Wherefore it follows that the entire active operation is on the part of the male, and the passive on the part of the female. For this reason in plants, where both forces are mingled, there is no distinction of male and female.
Since, therefore, the Blessed Virgin was not Christ's Father, but His Mother, it follows that it was not given to her to exercise an active power in His conception: whether to cooperate actively so as to be His Father, or not to cooperate at all, as some say. whence it would follow that this active power was bestowed on her to no purpose. We must therefore say that in Christ's conception itself she did not cooperate actively, but merely supplied the matter thereof. Nevertheless, before the conception she cooperated actively in the preparation of the matter so that it should be apt for the conception.
Reply to Objection 1: This conception had three privileges---namely, that it was without original sin; that it was not that of a man only, but of God and man; and that it was a virginal conception. And all three were effected by the Holy Ghost. Therefore Damascene says, as to the first, that the Holy Ghost "came upon the Virgin, purifying her"---that is, preserving her from conceiving with original sin. As to the second, he says: "And bestowing on her the power to receive," i.e. to conceive, "the Word of God." As to the third, he says: "And to give birth" to Him, i.e. that she might, while remaining a virgin, bring Him forth, not actively, but passively, just as other mothers achieve this through the action of the male seed.
Reply to Objection 2: The generative power of the female is imperfect compared to that of the male. And, therefore, just as in the arts the inferior art gives a disposition to the matter to which the higher art gives the form, as is stated Phys. ii, so also the generative power of the female prepares the matter, which is then fashioned by the active power of the male.
Reply to Objection 3: In order for a transformation to be natural, there is no need for an active principle in matter, but only for a passive principle, as stated above.