This thread was initiated in response to specific claims by Yankee_drifter.
Four Positive Proofs of the Perpetual Virginity of Mary
Proof #1 - The Vow of Perpetual Virginity
First, at the annunciation, the angel said that she would conceive and bear a son, she asked, “How can this be, since I do not know man?” She knew how babies were made, and she was about to be married. “How can this be?” would seem like a pretty silly question unless she had made a prior vow of virginity.
So, Why is she betrothed to Joseph if she made a vow of virginity?
Consecrated virginity was not common among first century Jews, but it did exist. According to some early Christian documents, such as the Protoevangelium of James (written around A.D. 120), Mary was a consecrated virgin. As such, when she reached puberty, her monthly cycle would render her ceremonially unclean and thus unable to dwell in the temple without defiling it under the Mosaic Law. At this time, she would be entrusted to a male guardian. However, since it was forbidden for a man to live with a woman he was not married or related to, the virgin would be wed to the guardian, and they would have no marital relations. Joseph agreed to marry Mary as her guardian - not as her husband - because he was much older and a widower. See Proof #3 below.
Proof #2 - The Absence of Younger Siblings in Childhood Scenes
When Jesus was found in the Temple at age twelve, the context suggests that he was the only son of Mary and Joseph. There is no hint in this episode of any other children in the family (Luke 2:41–51). Jesus grew up in Nazareth, and the people of Nazareth referred to him as “the son of Mary” (Mark 6:3), not as “a son of Mary.” In fact, others in the Gospels are never referred to as Mary’s sons, not even when they are called Jesus’ “brethren.” If they were in fact her sons, this would be strange usage.
Proof #3 - The Presence of Older Siblings by Joseph’s First Marriage
Also, the attitude taken by the “brethren of the Lord” implies they are his elders. In ancient and, particularly, in Eastern societies (remember, Palestine is in Asia), older sons gave advice to younger, but younger seldom gave advice to older—it was considered disrespectful to do so. But we find Jesus’ “brethren” saying to him that Galilee was no place for him and that he should go to Judea so he could make a name for himself (John 7:3–4).
Another time, they sought to restrain him for his own benefit: “And when his family heard it, they went out to seize him, for people were saying, ‘He is beside himself’” (Mark 3:21). This kind of behavior could make sense for ancient Jews only if the “brethren” were older than Jesus, but that alone eliminates them as his biological brothers, since Jesus was Mary’s “first-born” son (Luke 2:7).
Proof #4 - Jesus Entrusts Mary to John
Consider what happened at the foot of the cross. When he was dying, Jesus entrusted his mother to the apostle John (John 19:26–27). The Gospels mention four of his “brethren”: James, Joseph, Simon, and Jude. It is hard to imagine why Jesus would have disregarded family ties and made this provision for his mother if these four were also her sons.