St. Jerome composed this essay against Helvidius, who stated that because the gospels mentioned Christ as having “sisters” and “brethren” the Virgin Mary must have had more children from Joseph her husband. In response Jerome asserts three propositions against Helvidius:

1) That Joseph was only putatively, not really, the husband of Mary.
2) That the “brethren” of the Lord were his cousins, not his own brethren.
3) That virginity is better than the married state.
- Summary from the preface