If Jesus had siblings, the Bible likely would have been written differently in several places to make this clear.

I’ve written about this general topic eight times previously in these pages. But I keep coming up with additional arguments from the Bible, in my apologetics efforts and in dialogue with Protestants who reject the Catholic doctrine in this regard.

One fascinating line of argument has to do with the “thought experiment” notion: “If in fact Jesus had siblings, then the Bible likely would have been written differently in several places to make this very clear.” This is true in a broad sense:

• Nowhere does the New Testament state that any of Jesus’ “brothers” (adelphoi) are the children of Jesus’ mother Mary, even when they are referenced together (cf. Mark 3:31 ff.; 6:3 ff.; John 2:12; Acts 1:14).
• In the New Testament, none of these “brothers” are ever called Joseph’s children, either.

Another way of putting it is to say that if Jesus had brothers and sisters (full siblings), we wouldn’t expect that any of the things such as the above two factors, and others I shall present below, would be the case. These are arguments from plausibility and probability.

If Jesus had brothers or sisters and he was the oldest, then he certainly would have had siblings at 12 years old, when his parents took him to Jerusalem for the Passover (Luke 2:41-50) — particularly since Mary was estimated to have been around 16 at his birth, which would make her still only around 28 at this time. We’re to believe that it makes sense that she bore her first child at 16 and then had no more from 16-28, and then more than four after that? That’s not very plausible at all.

None of these alleged siblings are in sight during this Passover (which the whole family would have been bound to observe in Jerusalem). Luke states (2:46) that the search for Jesus took three days before he was found in the Temple. Mary said, “Your father and I have been looking for you anxiously” (2:48, RSV). If other children had been with them, they certainly would have been looking, too — in which case, Mary would have likely said, “your father and I and your brothers and sisters have been looking for you anxiously.” But she didn’t say that.

Mark and Matthew (recording spoken words) described Jesus and his brothers in relation to Mary in the following way:

• Mark 6:3 — “Is not this the carpenter, the son of Mary and brother of James and Joses and Judas and Simon, and are not his sisters here with us?” And they took offense at him.
• Matthew 13:55 — “Is not this the carpenter’s son? Is not his mother called Mary? And are not his brothers James and Joseph and Simon and Judas?”

Note my use of italics, highlighting the singular use of “son” in describing Jesus. This would seem to (at the very least, possibly) suggest “only son.” It’s in the context of mentioning four of his “brothers” and also “sisters” in Mark. Now, if they are all understood to be — and were in fact — his siblings, why is he called “the son of Mary” and “the carpenter’s son”? Note also that in both passages, only he is called Mary’s “son” and also Joseph’s (in Matthew). The others are not.

It seems to me, as an argument from implausibility, that this is not the language we would expect God to inspire the evangelists to use — remember, we’re talking about divinely-inspired revelation — if, in fact, Jesus had siblings. It would have been easy as pie for these passages to read so clearly, so manifestly plain, that there never would have been any dispute about the nature of the “brothers” of Jesus. All it would have required was a few changes of words. I submit that the passages would have read something like the following, if Jesus had siblings:

• Mark 6:3 — “Is not this the carpenter, one of the sons of Mary, along with his brothers James and Joses and Judas and Simon, and are not his sisters here with us?” And they took offense at him.
• Matthew 13:55 — “Is not this one of the carpenter’s sons? Is not his mother and the mother of his brothers James and Joseph and Simon and Judas called Mary?”

There are at least three other similar passages, from the other two Gospel writers (Luke wrote the Book of Acts). I’ll add in brackets what arguably should have been added if there were other siblings:

• John 1:45 — “We have found him of whom Moses in the law and also the prophets wrote, Jesus of Nazareth, [one of] the son[s] of Joseph.”
• John 6:42 — They said, “Is not this Jesus, [one of] the son[s] of Joseph, whose father and mother we know? ...” 
• Acts 1:14 — All these with one accord devoted themselves to prayer, together with the women and Mary the mother of Jesus, and with his brothers [“... Mary the mother of Jesus and his brothers”].

See how in the latter, a distinction is made between Mary as the mother of Jesus and “his brothers,” who are not called Mary’s sons? Nor is she called their mother. These verses do not read in a “siblings” way. I’d like to ask those who deny Mary’s perpetual virginity: Why do you think that is? Why wouldn’t God have made it easy to understand and logically and grammatically impossible to deny, if Jesus had siblings? There were many opportunities and contexts in Holy Scripture where this could easily have taken place, but for some odd reason it never does. And so, 2,000 years later, we’re debating the issue, since Protestants in the late 17th and early 18th centuries decided to start denying that the Blessed Virgin Mary was a perpetual virgin.

When things like this (arguments from plausibility or probability) happen again and again, they achieve a cumulative effect, that make them stronger, taken together, just as a rope becomes stronger, the more strands it has.