Times change, and so do sexual mores, but you wouldn't know that from most modern historical fiction. While it is certainly true that people have had premarital sex, extramarital sex, sex without the end-goal of baby-making, and gay sex since the beginning of time, doing so (or at least getting caught) was, in many time periods, a Very Bad Thing. However, some writers of period fiction do not seem to realize this and thus their characters behave as though contemporary sexual mores (or even looser ones) exist in their historic worlds.
This is not to say that sex shouldn't happen in period fiction; on the contrary, sex happened a lot. Promiscuity is very, very well recorded through the ages. It was the attitudes about sex and its results that differed. For example, there is nothing historically inaccurate about a story set in Topeka in the 1930s about a married man having an affair. If, however, the mistress has his child, the child is acknowledged openly as his son, and everybody is perfectly fine with it, then the story would fall right into this trope. And, of course, if you throw race, ethnicity, social class (especially in non-democratic or only quasi-democratic societies), or something as politically charged as communism into the mix, the problem becomes even more acute. (It can be justified, however, if the story takes place in a bohemian setting or miles from civilization, or if all the characters are criminals or rogues not of the Family Values Villain variety.) Having said that, societies without effective birth control (which was most of them) usually looked unkindly on irresponsible baby-making, especially among those too poor to feed the resulting children. Put another way, it is not so much what the characters do as how it is treated by the other characters.
The only way for authors to avoid this trope is by researching the time and place in which the work is set and then employ Deliberate Values Dissonance as needed. Attitudes toward pre- and extra-marital sex and illegitimacy varied widely from class to class, time period to time period, and country to country. Writers also err when they show couples enthusiastically partaking in forms of sex more common now than in other time periods; prior to the mid-20th century, for example, most Americans were unaware there was any sexual position other than missionary.
Additionally, this may vary for social classes within the same culture; the virginity of women with Blue Blood was important not only because a noblewoman functioned as a living bargaining chip or political merger, but to distinguish them from the lower classes as untouched and pure. (And very few people have thought to justify a sexually-free noblewoman by having her pay people to shut up, or have her family call her exploits "bad rumors.") The sex life of a farmer/townswoman would basically be Beneath Notice to those of high status, since nobody was counting on her to make royal babies or cement an alliance with troublesome rivals. Of course, while it often led to a more relaxed view of sex/virginity among commoners, it also had the harsh cultural side-effect of making nobles think "peasant women are easy sluts" or "anyone can screw a farmgirl, it's not like they're important anyway." (Also note that this would be frequently if not Always Female— a man is not a virgin too long past puberty, after all.)
Inversion of this trope is not unknown, either: it's not impossible to find works which assume that every society anywhere in the world prior to the 1960s Western note "sexual revolution" was as prudish and negative - or even completely ignorant - about sexuality as a caricature of late-nineteenth-century England or the 1950s USA. Some younger and particularly naïve viewers might think that even the 1980s was a prudish time (which is understandable given the frequently lampshaded sociopolitical influence of the Moral Majority during that decade, but after all there were very good reasons for that group and others like it being up in arms).
- Subverted humorously in a Carl's Jr./Hardee's TV commercial in which a man in a suit, having apparently time-traveled from the antebellum South, shows up on a beach in the present day with a picnic basket full of Carl's/Hardee's new made-from-scratch biscuits. After sharing his biscuits with the shorts- and bikini-clad beachcombers, the first thing he wonders is why everyone is in their underwear. (Even more hilarious when you remember that underwear for both sexes in the Civil War era was more dowdy than any contemporary bathing suit, and that the only people in America at that time wearing anything resembling Speedos and bikinis were Native Americans; it's understandable that the time-traveler would assume something had gone awry.)
- In Samurai Champloo it's actually Lampshaded in one episode by the narrator reminding that Edo-period Japan had different sexual mores from the later Meiji-period when the Western influences started to creep in. Calling it more "liberal", however, would be simplistic — sure, homosexual relationships were tolerated and even valued. But rape was often used as a punishment or interrogation method on female criminals, pederasty was widespread and even encouraged, and the main reason homosexuality was accepted was misogyny (because why would you want to love a mere woman?).
- Played with in Victorian Romance Emma, what with the servant girls talking openly about their sexcapades and German immigrant Dorothea standing by a hotel window stark naked. Then again, this could be a subversion of Victorian sexuality, given how hypocritical it actually was.
- Lampshaded in The Ultimates volume three; it's set in the 21st century and when the implied and mostly humorous BrotherSister Incest between Quicksilver and Scarlet Witch was made explicit, Wasp chastised Captain America's "1940s brain" for being unable to comprehend it. And as one Cracked article put it: "we are quite sure incest existed back then, too." Not to mention, they were rather a bit more lenient back then on some of what we would call incest now. BrotherSister Incest was as unacceptable then as it is now, but first cousins married sometimes. It's still legal in many places.
- Goldie Vance takes place in the early 60's. Despite this nobody says anything about Goldie's love interest being another girl.
- In 9 Chickweed Lane, during the extended WWII flashback arc, Edna (a younger Gran) and her Austrian ex-POW lover Peter Kiesl got into Public Displays of Affection that, while perfectly in line with the strip's usual tone and would probably get them no more than a call of "Get a room," would have the cops on them in 1950s' New York City.
- Done in one terrible Polish Real-Person Fic about Tokio Hotel (sporked in Polish here and and here.), which re-imagines Bill and Tom Kaulitz as gay lovers... in Poland under Nazi occupation... with Tom being an SS officer and Bill being a Polish boy. Yeah. One of the most painful scenes comes when Tom introduces Bill to his parents as a "friend", and Tom's father figures out quickly that they're lovers, but all he has to say is "I have no right to tell you how to live your life, but don't be too overt with it because I don't want anybody to gossip." Of course, in real-life Nazi Germany, gossip would be very much the least of worries for a Nazi officer found to have a Slavic homosexual lover.
- For characters living in the 1980s, the characters in the Ranma 1/2 oneshot Everything's Changing are pretty accepting on queer issues. Akane's transgender feelings aren't given much note and neither is the relationship between Ranma and Akane. They even use terms like "ace-spectrum", which didn't become commonplace until the 2010s.
- The 1995 version of The Scarlet Letter imposes this trope on the Puritans, of all people, by portraying the main characters as feeling guiltless over their adultery. Roger Ebert breaks down just how far afield from the source material the film goes.
- Kingdom of Heaven has the hero and the queen in a sexual relationship despite her being married to someone else, and no-one questions the morality of this, even though the movie takes place in Middle Ages Jerusalem. Under the specific circumstances — the husband is politically and personally unpopular and the queen is the heir to the throne — many people, specifically Sybilla's adherents and Balian's followers, would be willing to wink at the relationship. Of course those who sided with the husband would not. While there is some indication the real Sybilla and Balian did indeed have an affair, it seems they were far more discreet about it.
- The Legend of Zorro is set in mid-19th century California. The wealthy and socially prominent main characters (Antonio Banderas, Catherine Zeta-Jones) get divorced, and the woman continues to raise their son and is apparently still socially prominent (and remember that this is Spanish-Mexican California, a Catholic culture, where divorce was even more intolerable than in Protestant countries, although loopholes did of course exist).
- Subverted in Lawrence of Arabia. Set in the early 1900s, Lawrence is ashamed that he's a bastard (his father didn't marry his mother) and tries to conceal it, and his Arab friend is clearly initially uncomfortable with it.
- Seth McFarlane's A Million Ways to Die in the West has a prudish Christian frontier prostitute (ironically portrayed by the very Jewish Sarah Silverman) happily servicing her many clients but forbidding premarital sex with her boyfriend — and the boyfriend's attitude toward this hypocrisy is not moral outrage, but simple jealousy. While 19th-century America was a lot more like today than many people think (the slang expression "kick some butt" already existed, and social problems such as sexually-transmitted diseases and gang activity were already present), the film deliberately anachronizes the setting for the sake of humor (not to mention the very last scene, wherein a black cowboy shows up at an all-white county fair, shoots one of the carnival barkers dead, and (presumably) suffers no consequences for it.
- Kinsey has a lot of fun playing with this one. It's 1947 and teaching human sexuality in public settings is forbidden, even at otherwise liberal state universities. In fact, Dr. Alfred Kinsey is a zoologist before beginning his infamous study. However, as Kinsey and his aides quickly discover, this hasn't prevented Americans of all varieties from "experimenting", and practitioners of masturbation, pedophilia, and worse soon come forward to tell them everything, some of them quite gleefully. This was a major source of the Real Life criticism of his reports, as many of the more prudish people in society would not take part with the interviews, whereas populations like male prostitutes and criminals were highly over-represented in his sample, leading many to question how representative his sample was of the population at large.
- Shakespeare in Love: Viola suffers no negative consequences as a result of her affair, though going by the mores of the time her reputation would have been irretrievably ruined. In reality Lord Wessex most likely would have canceled their engagement. Plus, no one else would marry her due to the stigma. However, as he's desperate to get money, going through with it might not be wholly unrealistic (though he would want to insure she hadn't gotten pregnant by Shakespeare). On that note, there's no indication that she ever fears either pregnancy or STDs, though the former would also cause her ruin and the latter could be deadly with syphilis then (it's theorized by some Shakespeare contracted it).
- Sally Lockhart: The Shadow in the North provides a relatively justified example - Sally's friends seem perfectly thrilled she's gotten pregnant outside marriage (after all, the baby is Frederick's) and don't even seem to worry that this might be difficult for her. Given that she's a London woman with a career during The Gay '90s, and whose friends tend towards the bohemian, this is fairly believable. Notably in the next book, The Tiger in the Well, this turns into a huge problem for her when a fake husband turns up and hardly anybody is willing to believe Sally's side of the story.
- Averted in Robert A. Heinlein's Time Enough for Love. While main character Lazarus Long travels back to 1916 and has copious sex with his mother, and they seem to have no issues with what they are doing, they both put a lot of effort into making sure the relationship appears chaste and wholesome to anyone else. Additionally, she knows that she is already pregnant from her husband, so she does not have to worry about contraception. Of course, Parental Incest was just as unacceptable when Heinlein was writing as it was in 1916.
- Diana Gabaldon's Outlander series does a pretty good job of subverting this in a historically appropriate manner, even if the books do involve a good bit of time travel. In one of the later books, Brianna Fraser (the heroine's 20th century daughter) loses her virginity to her 20th century boyfriend, and is raped shortly after by the book's 18th century Big Bad. And gets pregnant, from one of the two. Guess which one she can tell her 18th century, very Scottish, very angry father about? When the news does come out that she wasn't a virgin, there's a screaming match that almost reads like a Kick the Dog because she indulged her desire for sex. Extramarital sex, though her mother is concerned mostly by the lack of contraception, is BAD. And the heroic homosexual character "coming out" is Squick to the heroine, equivalent to him confessing to murdering puppies.
- Justified in Freedom and Necessity by Steven Brust and Emma Bull: Susan and Kitty's rather modern sexual mores are Hand Waved away — they're eccentric radical bohemians, and rather wealthy, so they are in a position to ignore "normal" 19th-century concerns about extra-marital sex, or being women living alone. Susan does comment that, having (chastely) sat up with a man overnight, her reputation would be gone if anyone knew about it.
- In Island in the Sea of Time, which takes place in a Bronze-Age world, the only thing that shocks Swindapa's parents about her interracial lesbian relationship with Marian Alston is that it's monogamous. Of course, her society is one that modern archaeologists know very little about, giving the author some wiggle room.
- Justified Trope in The Crocodile God. Filipino-American Mirasol has dreams about her past lives and her relationship(s) with the Tagalog sea-god Haik. In the newly-colonized Philippines, past-Mirasol is a housemaid to a Spanish family, and she marries Haik with a loose ceremony and no witnesses (unless you count the whales). Haik asks if she wants to get married, but not because he himself is bothered—it's because he doesn't want her master to "check" her virginity. She assures Haik that the family won't notice anything as long as she doesn't get pregnant, and while the Spaniard's wife worries about Mirasol having sex before marriage, Mirasol just shrugs and takes medicinal tea for contraception. In real-life, precolonial Filipinos were indeed less uptight before Spain arrived, and medieval Catholicism would have been ESPECIALLY strict. The REAL issue with marrying Haik is cultural due to how obviously indio he is—two years into the marriage, Mirasol's master pulls a gun on him the moment he spots Haik's extensive, extremely non-Catholic tattoos.
- Set in early 1800s America, Patience and Sarah doesn't feature a lick of gayngst from the titular protagonists but later subverts this. As it turned out, for all their Biblical reading, neither knew that most Christians at the time looked down upon lesbian relationships. It came as a surprise to Patience when she was read a few passages her sister-in-law believed discouraged homosexuality as a sin. Patience, Sarah, and a man who falls for Sarah's male disguise are the odd three out of their society who don't mind same-sex relationships.
- Averted somewhat with the second episode of New Amsterdam, during a flashback set in the early 1940s, where John produces a baby out of wedlock with a black woman named Lily. She gets fired when her employer sees her with a white man and previously had to enter the hotel where they met through a service elevator. Her father becomes very upset with them both, and says they can never make it in the world (at this point interracial marriage was illegal in most states, for onenote ). The hotel staff react more reasonably than you would expect in real life in the 1940s, but they may not have known John and Lily were together (or it might not have been completely uncommon if a white man had an affair with a black woman). Lily herself breaks it off, knowing they'll be together in the long run. It turns out like this after she gets pregnant, and when they reunite in the black hospital after she has their baby, there are some very pointed looks.
- M*A*S*H plays with this trope several different ways, depending on the character and the writer(s) of the episode. For the married Henry Blake and Trapper John, and early-season bachelor Hawkeye Pierce, Eternal Sexual Freedom is in full play; no one calls them out on their open and casual affairs. The married Frank Burns, on the other hand, is treated like scum for establishing an ongoing, if shallow, relationship with Margaret Houlihan, who gets the nickname "Hot Lips" out of it, although in their case this is more because they're Holier Than Thou hypocrites.note B.J. Hunnicutt, on the two occasions that he isn't completely faithful to his wife Peg, doesn't get a lot of judgment from the other characters; mostly, he pillories himself, though Hawkeye reacts angrily to his writing a letter confessing to Peg, saying it will only hurt her. Also, in later seasons Hawkeye's womanizing is (some times) deconstructed and he's shown as rather pathetic rather than as a positive example.
- That '70s Show: The program was set among ethnic (and presumably Protestant) whites in socially/culturally conservative suburban Wisconsin, where the new 1960s values were forbidden or only very grudgingly tolerated. Some of the show's later plots, while not actually incorrect, were very unlikely to happen, such as Hyde marrying a stripper and continuing to live with the Formans, or Eric and Donna getting caught having sex in the kitchen and suffering no repercussions. In all likelihood, those things wouldn't happen now.
- Averted in the episode "Out of Time" — the temporally-displaced characters have to be told about modern sexual mores, and each reacts differently.
- On the other hand, in the episode "Captain Jack Harkness", Jack dances with and kisses another man in public — in 1941 England without anyone so much as raising an eyebrow. Subverted when the man is implied to have been killed by his squadmates the next day and the death blamed on the Germans.
- Doctor Who:
- The two-parter "The Empty Child"/"The Doctor Dances" provided a nice aversion in Nancy, who was ashamed of having had a son out of wedlock.
- "Day of the Moon" has an inversion. Richard Nixon offers to assist Canton Delaware by working to overturn interracial marriage bans. Loving v. Virginia, which did so in real life, was decided June 12, 1967, while "Day of the Moon" is obviously set on July 20, 1969. Nixon wasn't offering to make it legal for Canton to marry a black spouse, he was offering to ensure Canton didn't get hounded out his government job for doing so. He backs down when he realizes that Canton was referring to a black male spouse however.
- Rome was filled with sex and violence, supposedly historically vetted. But while the show prides itself on well-researched use of Deliberate Values Dissonance, it also makes a few mistakes. For example, oral sex, referenced frequently with its Western connotations, was considered vulgar and disgusting by the otherwise-licentious Romans.note
- Spartacus: Blood and Sand: While Romans did have lots and lots of sex, the show still plays this trope straight in regards to its use of female on female relationships; while it wasn't unheard of for slaves to perform lesbian sexual acts in secret for their mistress's entertainment, and possible for her to join in, lesbianism was not considered appropriate by general society (in most cases, it was simply disbelieved to exist however). Male same-sex relations were legal, but frequently mocked and often socially unacceptable to some degree. The main issue for Romans was who penetrated in anal sex, with the latter usually being of a lower social class, younger or a slave. If a man of higher standing received anal sex this was considered a huge disgrace and could result in a loss of social status ("infamy"). This was the primary distinction in Roman thought then on sexuality-"dominant" and "submissive", not the person's sex or gender. In fairness, though this doesn't come up all the consensual relationships between men which we see are by non-Romans/slaves who probably wouldn't care. The Lex Scantinia might have penalized sex with a freeborn minor male, or having receptive anal sex, though it's unclear (and was not enforced much if so, mostly in harassing opponents). Also a large sexual appetite, as the show has frequently, was condemned medically and ethically (of any kind), which cuts against much of the depiction (at least for Romans) though of course this doesn't mean it didn't happen.
- Downplayed on an episode of Foyle's War with a gay, WW2-era RAF pilot. He feels a great deal of gayngst and has to stay closeted because he knows that if it gets out, they'll never let him fly another mission. He tries to get a girl to be his beard, but she's disgusted by him. It's a clever episode because the audience can see the tragedy of his situation without any Author Filibuster pointing it out. Still, it's only a partial aversion because Foyle himself, being the saintly gentleman that he is, has absolutely no problem with the fact that this guy is madly in love with Foyle, Jr. A bit of a stretch, but not completely implausible; while homosexual acts weren't legalized in the UK until 1967, efforts to decriminalize them had begun ten years earlier and public opinion began to shift earlier still, and, for example, Noël Coward was generally known to be gay (the law against homosexual acts was not enforced very actively even by then — Turing was prosecuted because he'd confessed to a policeman, and he'd been "out" to some of his colleagues since the War).
- Murdoch Mysteries:
- Emily Grace backs down from her wedding days before to hang with George Crabtree. Bonus points for this being set in the liberal 1890's.
- Attitudes to homosexuality seem closer to the 1960s than the 1900s; yes, it's illegal, but that's mostly used as an excuse to arrest people they want to charge with something else but can't, and is otherwise ignored.
- Somewhat subverted in The Musketeers. While seemingly everyone knows about Constance Bonacieux's affair with D'Artagnan without consequence, when D'Artagnan tries to convince her to leave her husband for him, Constance points out that since they wouldn't be able to get married, her life would be much harder and she wouldn't be entitled to anything if he dies in war.
- In Tropico 3, you can legalize same-sex marriage... in the 1950s. Granted, the Cold War is grafted on to an island with mostly 1980-2010 sensibilities anyway. Not to mention for the description of the edict, your adviser mistakenly uses the original definition of the word gay, prompting him to question the controversy of letting happy people get married.
- In The Sims Medieval no-one seems to object to premarital sex, promiscuity or same-sex relationships... in the Middle Ages.
- Fallen London takes place in the 1890s and lets you blithely engage in homosexuality, pre-marital sex, threesomes, etc. It even lets you have a same gender Constant Companion and nobody cares. Mind you, London has been dragged a mile underground by bats, people frequently don't stay dead, and there are Rubbery Men, Clay Men and devils walking the streets so maybe the population just has bigger things to worry about.
- Averted in Déjà Vu when it comes to cross-dressing. Wearing Sugar Shack's clothes in public will get you arrested or in the hotel, thrown out. It is the 1940s after all.
- In Hollywood Visionary, if your character engages in homosexual relationships, the only one who will take any note of it at all is Jonathan Creed. This game is set in The '50s at the height of the Red Scare, and Creed asks about your homosexual activities at a Congressional hearing - none of the other members of Congress take your sex life into account in any way. Nobody from Hollywood cares, of course, but - as you're not part of a big studio - this is Truth in Television.