According to the book, the majority of this world is covered by water called the "sea"!! And it says the "sea" is all salt water!! Eren:
Salt?! L-liar!! I mean, salt?! That would be a treasure trove! Merchants would've already exhausted the supply!! Armin:
No, that's the thing! The "sea" is so huge, it can't be depleted! Eren: That's just silly.
The world has suffered some kind of massive calamity
. Humanity has survived
, but at a great cost. In addition to the population decrease, much of humanity's knowledge about the world and how it works has been lost.
How can an author demonstrate the sheer scale of cultural, historical, and intellectual loss? By having the characters rediscover some scrap of information that is laughably common knowledge in the real world and react to this information with shock, disbelief, and amazement. Expect at least one character to become fascinated and obsessed with the rediscovered knowledge, vowing to travel off in search for whatever-it-is (if it's a location, animal, etc) or to try and build it (if it's a form of technology). Expect at least one other character to scoff at the implausibility
of these "facts" and question whether the long-dead writer of the text was just making stuff up.
A variant is where the characters (usually children) will hear the lost knowledge told to them by an elderly relative who remembers the days when this knowledge was common. Again, their reactions will range from rapt wide-eyed wonder to "Granny must be going senile."
Sometimes the common knowledge will be lost because that thing no longer exists in the future world (e.g.: a child asking her grandmother to tell her about that strange extinct creature called the "lion"), thus further demonstrating how far the world has regressed.
Compare Future Imperfect
, where the knowledge is still there but has been misinterpeted over the years. Not to be confused with Common Knowledge
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Anime and Manga
- The page quote is from Attack on Titan which takes place In a World where the last remnants of humanity are holed up in a walled off territory about the size of Texas, hiding in fear of the people-eating giants that have overrun the world. Information about the outside world is not only scarce — it's forbidden by the government, and Eren mentions that the book Armin is reading from is illegal to own.
- Played for laughs in Idiocracy. By the time of the dumbed down future, people have no concept how to care for plants, and think that sports drinks can care for them. The main character tries to explain the (basic) science behind it, but the knowledge flies over their heads, so he settles with telling him that he can talk to plants, and they told him they wanted water.
- In The Book of Eli, all copies of the Bible have been destroyed, to the point where a big driving force of the plot is various characters' attempts to protect or steal a rare surviving copy. Explained as after a terrible third world war nearly drove humanity to extinction, most of humanity decided that religion was to blame for all the world's ills and had all religious texts burnt. The ending reveals that Alcatraz has been converted into a printing factory, where some individuals protect and feverishly work to reprint any salvaged copies of the Bible, Qu'ran, Talmud etc.
- In WALL•E, when Captain McCrea (whose ancestors spent hundreds of years lounging around on the luxury space-ship Axiom after fleeing Earth) accesses the computer database, most of the facts he's getting all excited over are commonplace knowledge in the real world, like the definition of "dancing" and "farms".
- Played for laughs in Sleeper. Miles Monroe wakes up in the year 2173 after spending 200 years as a Human Popsicle. The people of that time have lost most of their historical knowledge due to a nuclear war, so they ask him questions about 20th century artifacts (e.g. "chattering teeth") and people. Miles makes up a bunch of lies about them for his own amusement ("Bela Lugosi...was the mayor of New York for a while." and "Charles de Gaulle...was a very famous French chef."}.
- In The City of Ember, the simple fact that the surface world exists becomes Lost Common Knowledge, as does the existence of animals, candles, matches, the sun, the sky, and many other things.
- In "The People of Sparks", the Emberites don't know that the Earth is round, and don't know things like animals, trees, trucks, rain, seasons, and gods.
- In fact, this is the whole point of The Giver. The title character's actual occupation is "Receiver of Memory," and his role in the community is to be the only one with access to Lost Common Knowledge (such as the existence of death, color, and animals), in case it comes in handy to the regime. For example, the Giver tells Jonas that he was consulted when the powers that be were considering increasing the number of children born, and he said no because he knew why they'd started controlling population numbers, to avoid starvation. Of course he and Jonas come to feel that everyone else is being deprived of the knowledge of good things and that they're unfairly burdened being the only ones to know about things like starvation.
- Taken to an extreme in Ayn Rand's novella "Anthem"- the hero protagonist rediscovers the very concept of individuality and the word "I".
- In the dystopian world of the Delirium Series, where love is considered a disease, the protagonist Lena does not know what poetry is. She considers it to be incredibly beautiful when she hears it, however.
- Civilization has (sort of) recovered by the time of the Wheel of Time series' protagonists, but periodically they come across ideas or information that strike them as absurd. One villain is trying to distract one of the heroes, for instance, and mentions off-handedly that in her time, people were able to travel to other worlds, "even worlds in the sky". Only the last bit fazes Nynaeve, who's pretty familiar with other dimensions—but worlds in the sky? That's just ridiculous.
- Bonus points to the Aes Sedai who have spent thousands of years trying to figure out how ancient people could fly. They're certain it must have been a magical effect, but no one has ever managed it. It's on the verge of becoming discredited as a myth, possibly a mistranslated text. Perhaps the ancient Aes Sedai could fly that way, but only the reader (and a few Aiel, who don't become Aes Sedai) knows they had airplanes.
- An Instinct for War features a future Forever War in which American soldiers sees a page from Clausewitz's On War and dismisses it as being enemy propaganda as they can't read it.
- "The Quiz Broadcast" on That Mitchell and Webb Look is a post-apocalyptic gameshow that plays this for laughs. For example: "Pre-Event sources talk about "hope". What was hope?"
- Note that it is made clear that the gameshow takes place not that long after the Event. That's right: the Event was so horrible that people lost common knowledge of things they'd personally experienced for the bulk of their lives.
- In Star Trek: The Original Series, the episode "For The World Is Hollow And I Have Touched The Sky", the Fabrini built a generational starship into an asteroid to escape their dying homeworld. 10,000 years later, their descendants are completely oblivious to the fact they are living in space at all.
- Star Trek in general sometimes does this, with knowledge having been lost after the world war that devastated the earth and the cultural transformation brought on by replicators, the Federation, and alien influence. Unfortunately the writers don't always remember what things have been lost, so that the phrase "room service", which has been used several times in the shows without any hint that it's some archaic phrase, in one episode leaves the crew standing around in confusion until Data tentatively suggests that it's about cleaning the room.
- In the RPG Paranoia, most inhabitants of Alpha Complex display this attitude about anything relating to the semi-mythical Outdoors.
- In BIONICLE, the Matoran on Mata Nui use to live in the city of Metru Nui, but they lost all their memories of their old lives when the Makuta trapped them all wiped their memories so he could control them when they awaken. The Toa Metru awaken the Matoran by giving up their Toa powers, and guide them in tribal living as Turaga.
- A joke from Communist Eastern Europe: Somewhen in The Future, a child reads in an old book about butter. The child asks all people for the meaning, but nobody can remember. Finally, they find a definition in a dictionary: "A spread for bread, not used anymore by progressive people for its connotation with capitalism."