16 They have another cavil. “The generations of Christ,” say they, “are numbered through Joseph, and not through Mary.” Attend awhile, holy brethren. “It ought not to be,” they say, “through Joseph.” And why not? Was not Joseph the husband of Mary? “No,” they say. Who says so? For the Scripture says by the authority of the Angel that he was her husband. “Fear not to take unto you Mary your wife, for That which is conceived in her is of the Holy Ghost.” Again, he was commanded to name the Child, though He was not born of his seed; “She shall bring forth a Son, and you shall call His name Jesus.” Now the Scripture is intent on showing, that He was not born of Joseph's seed, when he is told in his trouble as to her being with child, “He is of the Holy Ghost;” and yet his paternal authority is not taken from him, forasmuch as he is commanded to name the Child; and again the Virgin Mary herself, who was well aware that it was not by him that she conceived Christ, yet calls him the father of Christ.
Source: Sermons on Selected Lessons of the New Testament (New Advent)