Reply Obj. 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 Obj. 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. _______________________
FOURTH ARTICLE [III, Q. 32, Art. 4]
Whether the Blessed Virgin Cooperated Actively in the Conception of
Christ's Body?
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.
Obj. 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.
Obj. 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.