Luke 2:33: "His father and mother
were wondering at those things which were spoken concerning Him": and
further on (Luke 2:48) in the same chapter she says: "Behold I and
Thy father [Vulg.: 'Thy father and I'] have sought Thee sorrowing."
Therefore Christ was not conceived of a virgin mother.

Obj. 2: Further (Matt. 1) it is proved that Christ was the Son of
Abraham and David, through Joseph being descended from David. But
this proof would have availed nothing if Joseph were not the father
of Christ. Therefore it seems that Christ's Mother conceived Him of
the seed of Joseph; and consequently that she was not a virgin in
conceiving Him.

Obj. 3: Further, it is written (Gal. 4:4): "God sent His Son, made of
a woman." But according to the customary mode of speaking, the term
"woman" applies to one who is known of a man. Therefore Christ was
not conceived by a virgin mother.

Obj. 4: Further, things of the same species have the same mode of
generation: since generation is specified by its terminus just as are
other motions. But Christ belonged to the same species as other men,
according to Phil. 2:7: "Being made in the likeness of men, and in
habit found as a man." Since therefore other men are begotten of the
mingling of male and female, it seems that Christ was begotten in the
same manner; and that consequently He was not conceived of a virgin
mother.

Obj. 5: Further, every natural form has its determinate matter,
outside which it cannot be. But the matter of human form appears to
be the semen of male and female. If therefore Christ's body was not
conceived of the semen of male and female, it would not have been
truly a human body; which cannot be asserted. It seems therefore that
He was not conceived of a virgin mother.

_On the contrary,_ It is written (Isa. 7:14): "Behold a virgin shall
conceive."

_I answer that,_ We must confess simply that the Mother of Christ was
a virgin in conceiving for to deny this belongs to the heresy of the
Ebionites and Cerinthus, who held Christ to be a mere man, and
maintained that He was born of both sexes.

It is fitting for four reasons that Christ should be born of a
virgin. First, in order to maintain the dignity or the Father Who
sent Him. For since Christ is the true and natural Son of God, it was
not fitting that He should have another father than God: lest the
dignity belonging to God be transferred to another.

Secondly, this was befitting to a property of the Son