A four-cornered marriage is a type of group marriage involving four people. American science fiction author Robert Heinlein who regularly featured polyamorous characters in his works is usually credited for coining the term.
Most often, a four-cornered marriage involves two men and two women. However, four individuals of any gender and sexuality can enter a four-cornered marriage.
For many people in a quad, a committed polyamorous relationship involving four people, a four-cornered marriage is the next natural step in their relationships. However, some quads may be happy with their relationship status and never enter into a four-cornered marriage.
Just like with a quad, the people in a four-cornered marriage may or may not be sexually involved with all the other members of the relationship, or only select members. However, unlike a quad, there should be a level of emotional involvement between all the individuals in a marriage. This will not necessarily be a romantic love, but it should involve at least a platonic love and commitment. Anecdotal evidence suggests that in the common four-cornered marriage with two men and two women, the two women are more likely to explore a sexual relationship together than the two men, who may simply seek out a type of brotherhood.
It’s important to note that in most parts of the world, the marriage of a four-cornered marriage is not legal, due to restrictions concerning bigamy and other multiple marriages. However, often the people in a four-cornered marriage have a commitment ceremony, which resembles a legal marriage, and then live in similar domestic partnerships. For example, the people in four-cornered marriages may share household chores and expenses, raise children together, and rely on one another for mental and emotional support.
