A frequent setup for romantic comedies and sometimes dramas, this trope explores the romantic relationships between four principal characters. By far the most frequent version is to have a Gender-Equal Ensemble with two male and two female lovers, but other versions are possible too.
If the lovers are not already paired up, they will get together during the course of the story, and the progress of each relationship may be used as a foil or yardstick for the other. There may be a clear Alpha and Beta Couple, or the two couples may be equally important in the story.
Whether or how the lovers pair up may, on the other hand, only be resolved near the end of the story, although it will probably be hinted at early on by the chemistry between them. Unlike Two Guys and a Girl and Two Girls and a Guy, this arrangement offers (and most often fulfills) the potential for romantic resolution without involving any additional people. Occasionally there may be transfers of affection within the foursome before the final resolution.
Each of the four lovers will be previously acquainted with at least one of the other three. The four may be staunch friends who spend a lot of time together, or there may be rivalry involved. In the case of a gender-balanced foursome with two heterosexual pairings, the same-gender characters may be Heterosexual Life-Partners, sometimes with subtle or not-so-subtle hints of Ho Yay. There may also be sibling relationships within the group.
- Toradora! begins on the basis that Ryuji and Taiga both like the other's best friend, and thus want to go out with them. Averted in that it doesn't happen in the end.
- At the beginning of Princess Tutu, Rue and Mytho are in a relationship, Fakir and Mytho are basically like brothers (interpret that as you will), and Duck has a major crush on Mytho. Add a couple of SecretIdentities to the mix and you've got one big (un)happy Love Dodecahedron.
- The yuri manga Haru Natsu Aki Fuyu centers on two pairs of Schoolgirl Lesbians, who are introduced after each other but become equally important in the course of the series. There is also a third Beta Couple consisting of their teachers.
- Certain fan works based on The Chronicles of Narnia create an alternative scenario in which Peter, Susan, Edmund and Lucy are not all blood siblings, opening up the potential for non-incestuous romantic pairings. The chemistry between the actors in the films, and particularly the Not Love Interest relationship between Edmund and Lucy in the third film, may have been shipping fuel for this treatment.
- The two main pairings in All This Sh*t is Twice as Weird fall under this trope, being comprised of two pairs of friends who knew each other for some time before meeting the other duo.
- Closer, the 2004 adaptation of a 1997 romantic drama play, is concerned with love triangles and infidelity between the very contrasting characters of Dan, Alice, Larry and Anna.
- The 2010 French romance film Happy Few (alternatively titled "Four Lovers"). The two couples decide to engage in partner-swapping, in order to explore the boundaries of their relationships.
- The 1971 comedy film Taking Off tells of how a couple's search for their runaway daughter leads them into contact with other parents in a similar situation. The two form a friendship with another couple, and all four take the opportunity to rediscover their youth together with marijuana and strip poker.
- The Fisher King has Jack Lucas and Anne, who help Parry and Lydia to get together. The former two act as matchmakers for the others.
- When Harry Met Sally...: Harry's best friend married Sally's best friend.
- The main characters of Follow the Fleet are sisters Connie and Sherry, and Navy buddies Bake and Bilge. They pair off as Bake/Sherry and Bilge/Connie (with a side order of Love Triangle in the latter case thanks to supporting character Iris).
- The novel Elective Affinities by Johann Wolfgang von Goethe has the aristocratic couple of Eduard and Charlotte, who like their landscape garden. Eduard invites his impoverished friend, the Captain, to help with the landscaping, and Charlotte her orphaned niece Ottilie to live with them. Soon attractions arise between Eduard and Ottilie and between Charlotte and the Captain. The novel does not have a happy end, but a novella-within-the-novel, which deals with a similar situation, does.
- Women in Love involves sisters Ursula and Gudrun, and their love interests Rupert and Gerald. In this case, both couples are foils for each other, and their romantic arcs take drastically different directions. In addition, an intense physical and emotional attraction between the two men is explored.
- Two married couples are vacationing on the eponymous island in Agatha Christie's short story Triangle at Rhodes, but an adulterous affair within the foursome is followed by a case of poisoning that Hercule Poirot must try to solve. It looks like an attempt to Murder the Hypotenuse, which it is, but the murderer and the intended victim are not who they first appear to be. This is either a darker variant or a deconstruction of the trope.
- This trope is invoked by the traditional cultural customs of Planet O in the eponymous story from Ursula K. Le Guin's short story collection, A Fisherman of the Inland Sea, where marriage is between four rather than two people: a man and a woman from each of two "moieties". Each same-moiety pairing is treated as a platonic sibling relationship, but all opposite-moiety pairings within the marriage, including the same-gender ones, are sexual.
- Used a few times in the Vorkosigan Saga by Lois McMaster Bujold:
- In Memory there are two forming couples: Gregor and Laisa, and Duv and Delia. Duv and Laisa were dating (though not romantically involved yet), when Gregor (Duv's superior) looped in and had a whirlwind romance with Laisa. Duv didn't take it well, but his quiet and unassuming style was noticed and appreciated by Gregor's old friend Delia. Though neither of the couples are the main characters of the novel. You can probably add Illyan and Alys as well, who also start a romance.
- In Captain Vorpatril's Alliance Ivan and Tej are the alpha couple, and Byerly and Rish are the betas. Ivan and Byerly are old acquaintances (with a somewhat belligerent friendship), and Tej and Rish are sisters.
- A Civil Campaign has far too many couples either just formed or forming up or just having trouble, all knowing each other: Miles and Ekaterin, Gregor and Laisa, Duv and Delia, Borgos and Martya, Dono and Olivia, Mark and Kareen... Note that Delia, Martya, Olivia, and Kareen are sisters.
- Freedom and Necessity forms couples of the old friends Richard and Kitty, and James and Susan.
- Jane Austen does this in two of her most popular works.
- In Pride and Prejudice, sisters Jane and Elizabeth Bennet eventually marry best friends Charles Bingley and Fitzwilliam Darcy. They even have a double wedding, just to hammer this trope home.
- In Sense and Sensibility, sisters Elinor and Marianne Dashwood eventually marry Edward Ferrars and Colonel Brandon, who by that time have been introduced and become good friends due to their similar temperaments and educations.
- Louisa May Alcott uses this in her most famous work, Little Women. Meg March marries the tutor John Brooke, while her younger sister Amy marries Theodore "Laurie" Laurence, John's student and close friend.
- Harry Potter is best friends with Ron Weasley and Hermione Granger. Ron and Hermione end up married, while Harry marries Ron's sister Ginny.
- The Good Life has the fun-loving adventurous Tom and Barbara Good, and their conventionally materialistic neighbors Jerry and Margo Leadbetter. Both couples are married, and the series follows how the relationships, as well as the sometimes-rocky friendships between the neighbors, develop as Tom and Barbara convert their house and garden into a self-sufficient farm. Although sexual tension is present between Barbara and Jerry, and to a lesser extent between Tom and Margo, both couples remain devoted.
- The O.C. has Ryan and Marissa, and Seth and Summer. Fans have fondly nicknamed them the "fab four", or "core four," with Ryan and Marissa being the angsty ship, and Seth and Summer being the sweet one. Bonus points that Ryan and Marissa started out as the cute ship, and Seth and Summer as the one that would never work.
- The first season of As Time Goes By involves this: Jean and Lionel were lovers separated 38 years ago by a misunderstanding. Now, Jean's daughter Judy is in love with Lionel, while Jean herself has an admirer in Lionel's young publisher Alistair. In the last episode of the season, the four of them go on a picnic, during which the two youngsters' attempts to be alone with their crush are thwarted. Lionel and Jean ultimately marry, as do Alistair and Judy.
- The episode "Who's Who?" of The Avengers (1960s) involves a pair of enemy agent lovers who swap bodies with Steed and Emma via a Grand Theft Me. The contrast between the heroes' UST-laden platonic relationship and the villains' overtly sexual one is played for laughs.
- Fairly typical setup on sitcoms:
- I Love Lucy had Lucy & Ricky and Fred & Ethel.
- The Honeymooners had Ralph & Alice and Ed & Trixie.
- Married... with Children started with Al & Peg and Steve & Marcie. After a brief hiatus when Steve was Put on a Bus, Marcie married Jefferson and the dynamic was restored.
- Bewitched involves Samantha & Darrin and Larry & Louise. Although both couples remain devoted, the four of them are subject to supernaturally-induced mishaps in some episodes, such as "Mixed Doubles" from Season 7.
- Riverdale has Betty and Jughead, and Archie and Veronica, commonly referred to as the "core four". Betty and Veronica are best friends, and so are Archie and Jughead. To complicate things, Betty and Archie are also best friends with a complicated and often confusing romantic history who get their own share of Ship Tease throughout the show.
- Shakespeare used this set-up a couple of times:
- In The Two Gentlemen of Verona, the two men begin as friends who could be seen as Ambiguously Gay, depending on the production. One, however, pulls a FaceHeel Turn as he abandons his own love interest and courts his friend's instead, betraying all three of the other characters in the process.
- The four lovers from A Midsummer Night's Dream. In this case, the men begin as rivals. The ultimate romantic resolution is implied early on, but only enacted near the end. Something of a Deconstruction, in that the happy ending required one of the men to be permanently affected with a love charm.
- Another Shakespeare example is Much Ado About Nothing, which features two contrasting couples: Hero and Claudio, the traditional romantic couple, and Beatrice and Benedick, whose relationship is full of Belligerent Sexual Tension. Claudio and Benedick are best friends, while Hero and Beatrice are cousins who have essentially been raised as sisters. Each couple makes frequent jokes and comments about the relationship between the other couple.
- As You Like It has brothers Orlando and Oliver falling for cousins Rosalind and Celia. Orlando and Rosalind are the Alpha Couple whose complicated courtship involves separation and disguise, while Oliver starts off evil and pulls a HeelFace Turn.
- Jack, Algernon, Gwendolyn and Cecily from The Importance of Being Earnest. Although there are two pairings with mutual love, this play is a satire of, among other things, romantic comedies involving this trope, as break-ups and make-ups happen frequently and for absurd reasons. There is also a long-term friendship and considerable Ho Yay between the men.
- Mozart also used this trope in several operas:
- The four principal characters in Così Fan Tutte. The two men test the fidelity of their wives by disguising themselves and courting each other's wives.
- Susanna and Figaro are happily engaged in The Marriage of Figaro, but Susanna is also being pursued by the Count, to the distress of his wife. Here it is the two women who swap clothes, in order to carry out a Bed Trick.
- Il Re Pastore ("The Shepherd King") has couples Aminta and Elisa, and Agenore and Tamiri, who are unwaveringly in love throughout, but their marriage plans are temporarily threatened by royal duties, politics, and the orders of King Alessandro, a Reasonable Authority Figure who eventually allows the four to follow their hearts.
- The second act of the musical Romance Romance, called "Summer Share", involves two young married couples - Sam, Barb, Monica and Lenny - who are spending a season together in a rented cottage; an affair develops slowly between Sam and Monica, escalating from an innocuous flirtation. This act was based on Jules Renard's 1898 play, Le pain de ménage.
- The opera La Bohème has Mimi, Rodolfo, Marcello and Musetta. The two couples' romantic arcs take different directions. Despite Rodolfo repulsing the terminally ill Mimi under false pretenses so that she can seek a wealthier lover to care for her, she dies peacefully surrounded by the other three.
- In Who's Afraid of Virginia Woolf?, bitter and frustrated married couple George and Martha invite a naive younger couple, Nick and Honey, for dinner in order to involve them in their dysfunctional relationship mind games; it is implied that Martha has a fling with Nick before the third act. In the end, all four characters come to a better understanding of their own marriages; Nick and Honey leave, and George and Martha ambiguously reconcile.
- While it may have only been hinted at in the original series, generations of Fanon have slowly Canonized this relationship among the Scooby-Doo Gang as of Scooby-Doo! Mystery Incorporated.
- The four principal characters of The Flintstones are the titular Flintstones, Fred and Wilma, and their Beta Couple best friend next door neighbors Barney and Betty Rubble.