In Leviticus 10:4 the first cousins of Aaron are termed "brethren," but this instance does not justify the constant use of the word in the Gospels for a definite group of persons as brothers of Jesus if they were only cousins. Besides, they appear constantly with Mary, the mother of Jesus, as members of her family. The use of "sisters" increases the argument for the common use of the word (Mark 6:3; Matt. 13:56). There are many other difficulties in the way of this position, such as the fact of two sisters with the name of Mary and the identification of Alphaeus and Clopas.
The theory that James and the other brothers and sisters were all children of Joseph by a former marriage (step-brother theory) is free from the difficulty about the word "brother" and is not inconceivable in itself. Unfortunately there are critical objections to it, for Jesus is not called "only begotten" of Mary but "firstborn" in Luke 2:7: "She brought forth her firstborn son."
Jesus is "only begotten" of God (John 1:18), as the widow of Nain had an only son (Luke 7:12) and Jairus an only daughter (Luke 8:42). But "firstborn" occurs in the true sense all through the Septuagint (cf. Gen. 27:19, 32; 43:33; Deut. 21:15), where there were other children. The inscriptions show it in the true sense. The New Testament instances of "firstborn" are all strictly correct from this standpoint, even Colossians 1:15 and Romans 8:29. "Firstborn" implies other children. Besides, the natural meaning of Matthew 1:25 leads to the same conclusion.
The theory (brother or half-brother theory) that Jesus and James were sons of the same mother, Mary, may be said to hold the field against the others. In fact, it is most likely that both of the other theories grew out of the desire to secure a greater imaginary sanctity for Mary under the impression that she was more holy if she bore only Jesus and did not live as wife with Joseph. But this is contrary to all Jewish sentiment, and certainly there is nothing in the Gospels to countenance this notion but much to contradict it. We conclude, therefore, that James, the author of the epistle, is the brother of Jesus.
In spite of Origen's opinion (Origen on Matt. 13:55) that the sons and daughters of Joseph were children of a former marriage, an opinion more than offset by the position of Tertullian (_de Monog. 8_, _de Virg. Vel. 6_), we must think of the family circle at Nazareth as composed of five brothers (Jesus, James, Joses, Judas, Simon, as in Mark 6:3, but Jesus, James, Joseph, Simon, Judas in Matt. 13:55) and the "sisters." Every implication is that they all passed as sons and daughters of Joseph and Mary in the usual sense. The order implies also that while Jesus was the eldest, James came next among the brothers. Unfortunately, the names of the sisters are not given.