In a certain society, there are two marriage groups, Red and Brown. No…
2025
In a certain society, there are two marriage groups, Red and Brown. No marriage is permitted within a group. On marriage, males become part of their wife’s group; women remain in their own group. Children belong to the same group as their parents. Widowers and divorced males revert to the group of their birth. Marriage to more than one person at the same time and marriage to a direct descendant are forbidden.
Which of the following is not permitted under the rules as stated?
- A.
A Brown male marrying his father’s sister
- B.
A Red female marrying her mother’s brother
- C.
A man born Red, who is now a widower, marrying his brother’s widow
- D.
A widower marrying his wife’s sister
Attempted by 5 students.
Show answer & explanation
Correct answer: B
Concept
Two rules fix everyone's group at the moment of marriage: a woman keeps her own birth group for life, while a man is always standing in his own birth group immediately before he marries — whether it is his first marriage, or a remarriage after being widowed or divorced, since widowers and divorced men revert to their birth group. Marriage is only allowed between two people who are currently in different groups, so whoever a man marries must have been born into the opposite group from his own birth group. Applying this to a family, every full sibling shares the same birth group, since they were all born while their parents held one common group.
Application
Proposed marriage | Birth groups worked out from the rules | Same group or different? |
|---|---|---|
A Brown male and his father’s sister | For the man to be in Brown, his father had to marry into it from the opposite group, Red. So the father was Red-born, and his sister shares that birth group: Red. | Brown vs Red — different |
A Red female and her mother’s brother | She is Red-born (women never change groups), so her parents shared the Red group at her birth — her mother is Red-born. Her mother’s brother comes from the same birth family, so he is Red-born too. | Red vs Red — same |
A man born Red (now a widower) and his brother’s widow | As a widower he has reverted to Red. His brother, from the same birth family, is Red-born too, and could only have married a Brown-born woman — so the brother’s widow is Brown-born. | Red vs Brown — different |
A widower and his (late) wife’s sister | The widower has reverted to his own birth group. His late wife had to have been born into the opposite group for their original marriage to be valid, and her sister — from the same birth family — shares that opposite group. | Opposite groups — different |
Cross-check
The one test that matters throughout is whether the two people are currently in different groups; every case above reduces to comparing two birth groups by this same rule. Three of the four pairings cross groups and are allowed. Only the pairing of a Red female with her mother’s brother puts two Red-born people together — exactly the intra-group marriage the rules forbid — so that is the one that is not permitted.