There are about ten instances in the New Testament where “brothers” and “sisters” of the Lord are mentioned: Matthew 12:46, Matthew 13:55, Mark 3:31–34, Mark 6:3, Luke 8:19–20, John 2:12, John 7:3–10, Acts 1:14, and 1 Corinthians 9:5.
When trying to understand these verses, note that the term brother (Greek: adelphos) has a wide meaning in the Bible. It is not restricted to the literal meaning of a full brother or half-brother. The same goes for sister (adelphe) and the plural form brothers (adelphoi). The Old Testament shows that the word for “brother” had a wide semantic range of meaning and could refer to any male relative from whom you are not descended (male relatives from whom you are descended are known as “fathers”) and who are not descended from you (your male descendants, regardless of the number of generations removed, are your “sons”), as well as kinsmen such as cousins, those who are members of the family by marriage or by law rather than by blood, and even friends or mere political allies (cf. 2 Sam. 1:26; Amos 1:9).
Lot, for example, is called Abraham’s brother (cf. Gen. 14:14), even though, being the son of Haran, Abraham’s brother (cf. Gen. 11:26–28), he was actually Abraham’s nephew. Similarly, Jacob is called the brother of his uncle Laban (cf. Gen. 29:15). Kish and Eleazar were the sons of Mahli. Kish had sons of his own, but Eleazar had no sons, only daughters, who married their “brethren,” the sons of Kish. These “brethren” were really their cousins (1 Chr. 23:21–22).
The terms for “brothers,” “brother,” and “sister” did not refer only to close relatives. Sometimes they meant kinsmen (cf. Deut. 23:7; Neh. 5:7; Jer. 34:9), as in the reference to the forty-two “brethren” of King Azariah (cf. 2 Kgs. 10:13–14).
"No Word for “Cousin”
Because neither Hebrew nor Aramaic (the language spoken by Christ and his disciples) had a special word meaning “cousin,” speakers of those languages could use either the word for “brother” or a circumlocution, such as “the son of my uncle.” But circumlocutions are clumsy, so the Jews often used the word for “brother.”
The writers of the New Testament were brought up using the Aramaic equivalent of “brothers” to mean both cousins and sons of the same father—plus other relatives and even non-relatives. When they wrote in Greek, they did the same thing the translators of the Septuagint did. (The Septuagint was the Greek version of the Hebrew Bible; it was translated by Hellenistic Jews a century or two before Christ’s birth and was the version of the Bible from which most of the Old Testament quotations found in the New Testament are taken.)
In the Septuagint the Hebrew word that includes both brothers and cousins was translated as adelphos, which in Greek usually has the narrow meaning that the English brother has. Unlike Hebrew or Aramaic, Greek has a separate word for cousin, anepsios, but the translators of the Septuagint used adelphos, even for true cousins.
You might say they transliterated instead of translated, importing the Jewish idiom into the Greek Bible. They took an exact equivalent of the Hebrew word for “brother” and did not use adelphos in one place (for sons of the same parents), and anepsios in another (for cousins). This same usage was employed by the writers of the New Testament and passed into English translations of the Bible. To determine what brethren or brother or sister means in any one verse, we have to look at the context. When we do that, we see that insuperable problems arise if we assume that Mary had children other than Jesus.
When the angel Gabriel appeared to Mary and told her that she would conceive a son, she asked, “How can this be, since I have no husband?” (Luke 1:34). From the Church’s earliest days, as the Fathers interpreted this Bible passage, Mary’s question was taken to mean that she had made a vow of lifelong virginity, even in marriage. (This was not common, but neither was it unheard of.) If she had not taken such a vow, the question would make no sense.
Mary knew how babies are made (otherwise she wouldn’t have asked the question she did). If she had anticipated having children in the normal way and did not intend to maintain a vow of virginity, she would hardly have to ask how she was to have a child, since conceiving a child in the natural way would be expected by a newlywed wife. Her question makes sense only if there was an apparent (but not a real) conflict between keeping a vow of virginity and acceding to the angel’s request. A careful look at the New Testament shows that Mary kept her vow of virginity and never had any children other than Jesus.
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 (cf. 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.
Also, the attitude taken by the “brethren of the Lord” implies that 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).
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.
