But there seems to be no obstacle to a man's marrying the
daughter of a woman whom his father has adopted, for she is
no relation of his by either natural or civil law. 4 The children
of two brothers or sisters, or of a brother and sister, may lawfully
intermarry. 5 Again, a man may not marry his father's sister,
even though the tie be merely adoptive, or his mother's sister:
for they are considered to stand in the relation of ascendants.
For the same reason too a man may not marry his great-aunt
either paternal or maternal. 6 Certain marriages again are pro-
hibited on the ground of affinity, or the tie between a man or his
wife and the kin of the other respectively. For instance, a man
may not marry his wife's daughter or his son's wife, for both are
to him in the position of daughters. By wife's daughter or son's
wife we must be understood to mean persons who have been
thus related to us; for if a woman is still your daughter-in-law,
that is, still married to your son, you cannot marry her for
another reason, namely, because she cannot be the wife of two
persons at once. So too if a woman is still your stepdaughter,
that is, if her mother is still married to you, you cannot marry her
for the same reason, namely, because a man cannot have two
wives at the same time. 7 Again, it is forbidden for a man to
marry his wife's mother or his father's wife, because to him
they are in the position of a mother, though in this case too our
statement applies only after the relationship has finally terminated;
otherwise, if a woman is still your stepmother, that is, is married
to your father, the common rule of law prevents her from
marrying you, because a woman cannot have two husbands at
the same time: and if she is still your wife's mother, that is, if her
daughter is still married to you, you cannot marry her because
you cannot have two wives at the same time. 8 But a son of the