''The Encyclopedia is, and always has been, a fraud. In the 50 years you have worked on this fraudulent project, your retreat has been cut off, and you have no choice but to proceed with the project that was, and always has been, our real plan. Terminus, and its companion Foundation at the other end of the galaxy, are to be the seeds and founders of the Second Galactic Empire.
— Hari Seldon
The "Foundation Trilogy" is a classic collection of science fiction stories by the author Isaac Asimov: Foundation, Foundation and Empire and Second Foundation.Famous mathematician Hari Seldon creates the science of "psychohistory", which can be used to predict the broad sweep of humanity's future. Said future is not looking good: the Galactic Empire in which Seldon lives is in terminal decline, with nothing to follow but barbarism for the next thirty thousand years. In order to accelerate a return to civilization, Seldon and his followers establish two Foundations to preserve human knowledge, at "opposite ends" of the galaxy. In order to keep its actions predictable, the first of these colonies originally has no idea of Seldon's real plan, but is banished from the imperial capital Trantor to the planet Terminus on the remote edge of the galaxy, there officially assigned to compose an encyclopedia of all human knowledge. The Second Foundation remains nearly forgotten, cloaked in secrecy.As the decades pass and their power grows, the leaders of "the" Foundation time and again find themselves facing a major crisis, usually having to do with their relationships with the semi-barbarous star systems which surround them, the political rubble left behind by the Empire's ongoing collapse. Seldon's "Plan" dictates that each crisis will force events down one inevitable path, which will invariably cause a drastic change in both the Foundation itself and its relationship with the nations surrounding it. During these Crises, the long-dead Seldon always steps in with a recorded message telling the current generation of Foundationers what they need to hear (or a summary of the recent past), as he has predicted it decades previously. All goes well, at least as far the Foundation is concerned, until a very singular individual nicknamed "The Mule" suddenly appears on the galactic scene...Asimov also wrote three "Empire novels": Pebble in the Sky, The Stars, Like Dust and The Currents of Space, each set at various points during the long stretch of history when humanity reaches out from Earth, and a Galactic Empire rises to power. These stories were originally written as a separate trilogy but later acknowledged to be about the same Empire that appears in the Foundation series.Then there's Asimov's "Robot" series, featuring the famous "Three Laws of Robotics". Mostly composed of short stories exploring the various relationships between robots and their human creators, which, despite the robots essentially being benevolent and altruistic, develop into a human-robot conflict as certain exceptional robots learn to transcend the laws that keep them in servitude, inventing a "0th Law" which puts them under the jurisdiction of humanity rather than individual humans.The Foundation series was continued almost 30 years later with two books, Foundation's Edge and Foundation and Earth both set in the same era and following the adventures of Foundationer Golan Trevize, who is joined by historian Janov Pelorat in a search for humanity's origin planet, Earth (actually a secret search for the Second Foundation). The issue with the Second Foundation and a mysterious third power called Gaia is resolved at the end of the fourth book, and the pair gains a new companion (and love interest for Pelorat) in the telepathic Gaian, Bliss. The fifth book details the search for Earth and concludes with a Twist Ending, where it is confirmed that the heroes are in the same universe as the Empire and Robot books. This was further elaborated on in the final Robot book, Robots and Empire.Unable to come up with a continuation, Asimov instead turned to prequels. Prelude to Foundation chronicles the youth of Hari Seldon and contains further explicit ties to the Robot series. The final book, Forward the Foundation is about Seldon's final days as he attempts to perfect his theory and deal with his unwilling entry into politics, even he is slowly losing everyone important to him. As Asimov wrote the book shortly before his death it is noticeably different from the rest of the series, with Seldon becoming Asimov's literary alter ego.After Asimov's death, three of his fellow sci-fi writers, Gregory Benford, Greg Bear, and David Brin, each wrote a book in a trilogy detailing more of the younger Seldon's adventures: Foundation's Fear, Foundation and Chaos and Foundation's Triumph. In addition, several Foundation short stories can be found in the tribute anthology Foundation's Friends.The exact point at which this all drifts into Fanon Discontinuity, if ever, is up to the individual reader.The winner of the special one-time Hugo Award for "best series," though afterwards Asimov himself stated it should have gone to The Lord of the Rings.According to the Word of God (from George Lucas), the Empire in the Star Wars films was based on the Foundation Empire (and in fact, Asimov advised Lucas in the creation phase). Most obviously is the city-wide planet of Coruscant, which is an Expy of Trantor.Apparently, Roland Emmerich, of all people, is planning on making a film trilogy out of the first three books. Back in the 70's, the BBC did a Radio Drama adaptation which can be found on the Internet Archive.
Contains examples of:
Absent Aliens: Humanity is the only sentient species in the galaxy. Unless you count robots, Gaians, or Solarians.
The first of which was created by humans, while the other two are descended from humans.
Explained by one of the (written by other authors after Asimov's death) books. the Zeroth law only applies to Humans. The robots killed off every other species in the galaxy remotely able to ever threaten humans. Of course, that never happened.
Agony Beam: The Neuronic Whip, which directly stimulates nerve receptors. This results in a rather warped conversation in Foundation And Earth; while exploring the ruins of a once-human-inhabited planet, the protagonists are attacked by mutated dogs. Trevize's Disintegrator Ray is almost useless, as the dogs appear to have no survival instincts and continue their assault no matter how many of them die. But when he hits them with the whip, they scatter at a slight telepathic nudge from Bliss. As Asimov considered violence to be perverse, even in self-defense, this is something of an Accidental Aesop.
Bliss: With a blaster, Trevize, a dog merely disappears. The rest may be surprised, but not frightened. ...The neuronic whip is different. It inflicts pain, and a dog in pain emits cries of a kind that are well understood by other dogs...
The reason why The Mule is so dangerous is because Seldon couldn't have planned for it. Psychohistory only works with groups, with the larger group the more accurate the predictions come due to sociological patterns. It was never designed to deal with a single immensely powerful individual, because psychohistory could never predict that a single individual could do everything purely on their own.
Artifact Title: In-universe example with "The Foundation". Originally called the Encyclopedia Foundation, it was an N.G.O. focusing on publishing the total sum of the Empire's knowledge. While it did eventually do that (sort of), The Foundation began to focus on its true purpose, and became a empire of its own.
Atom Punk: Everything progressive in the universe runs on "Atomics" in the first book, and "Nucleics" from the second book onward. Everything, from home appliances to starships.
Badass Bookworm: Hari Seldon, whose home planet of Helicon is noted for its martial arts.
Badass Pacifist: Hardin. Able to stop Anacreon from invading the Foundation by convincing the barbarous world that they will suffer divine intervention for it, and then gives a Kirk Summation after Wienis tries to use force, but is killed by his own weapon. Back on Terminus, Hardin's enemies no longer try to impeach him, just in time for Seldon's Vault to be opened again.
Became Their Own Antithesis: Salvor Hardin is introduced as the Only Sane Man who is the only person to realize that Terminus is vulnerable to the Four Kingdoms, and that the whole Galaxy, even in the parts that haven't collapsed yet, is going to stagnate because the scientific method has been almost forgotten. After he takes over the government, he turns science into a religion (though only for missionary purposes — the scientific method is still remembered and used on Terminus itself) and appears to appease the Four Kingdoms. This is lampshaded by the Actionist Party, his political opponents, who mention among themselves that Hardin was a committed Actionist back when he was their age.
Belief Makes You Stupid: At one point, the Foundation creates its own techno-religion to manipulate the populace of its neighbors. It's noted that the Foundation didn't mean to make a religion, that just turned out to be the best way to get their extremely backwards, unscientific neighbors to accept modern technology again. You can almost see the anonymous Foundationer creating the religion off-screen when he finally slaps his forehead and cries A Wizard Did It. It turns out to be a great way to distribute the technology while maintaining control of the actual knowledge base and science that makes it work.
Brainwashed: Victims of both The Mule and the Second Foundation.
Brick Joke: in The Caves of Steel, Daneel Olivaw has a problem in that his smile goes straight into the Uncanny Valley. Thousands of years later, he has to be taught how to chuckle (and it requires him weeks of training to achieve an apparently genuine result.
The Bro Code: Invoked by Golan Trevize in Foundation and Earth, to get an order agent to let Bliss enter a planet without documents.
Bunny-Ears Lawyer: Ebling Mis. The Foundation's top psychologist, he lives in a messy house, swears constantly, and has little to no respect for formality. Once, when dealing with a stuffy and bureaucratic mayor, he went so far as to sit on the man's desk.
The Butler Did It: In the last Foundation novel, Forward the Foundation (posthumously published) Emperor Cleon I, who was later considered the last emperor under whom the Empire prospered, was assassinated at age 50 by none other than his gardener Gruber who was distressed about his appointment to be the Head Gardener, as that was a desk job and he would be taken away from the outdoors.
The Chessmaster: Seldon, and then the Second Foundation, and then Gaia, and finally R. Daneel Olivaw
Contrived Coincidence: in "The Merchants", when Hober Mallow visits Korell, he is in a out-of-the-way spaceport, with the nearest city 150 kilometers away, when a priest appears, immediately followed by a mob. This fact clues Mallow in the fact that it is a ruse played by the Korell leaders to prevent the religion of science from spreading to their world.
Crew of One: Many of the smaller ships in the series, and Trevize's in particular.
The Cycle of Empires: The series starts as the Galactic Empire is in decline. The Foundation's entire purpose is to jump-start the formation of the next empire and cut the long night short by several thousand years.
Dashed Plot Line: Each book is spread out over several years, sometimes even multiple centuries
Deadly Upgrade: A scientist character whose ability to make intuitive logical leaps was overclocked in this way by an emotion-controlling telepath, which brought him to the brink of death.
Deconstruction: Of pulp era space operas. Instead of dashing heroics and swashbuckling, Asimov created a space opera where the heroes use their wits and intelligence to get out of problems. Indeed, the author goes so far that the indviduals themselves do not save the day, but historical forces are what do, sometimes beyond the protagonists' control.
Declining Promotion: Inverted. In one of the prequel novels the Emperor of the Galactic Empire is assassinated by a gardener he took a liking to. The gardener was promoted to Head Gardener over his protests - as Head Gardener he'd have to manage people and do paperwork instead of gardening, which is what he enjoys.
Didn't See That Coming: The Seldon Plan worked wonderfully for the first book and a half, but then it ran into a complete unknown unknown in the form of the Mule. The plan is eventually brought back on track through Xanatos Speed Chess, a massive Hail Mary pass on the part of the Second Foundation and the Heroic Sacrifice of many of their people. Later, another unknown unknown surfaced in the form of Gaia, and more generally, the fact that the Seldon Plan can't account for nonhuman intelligences, which are beginning to emerge through human evolution.
It's also implied that the Seldon Plan is based on very generalized human behavior, concentrating on mass movements and trends. The formula behind the Plan tends to disregard the effect a single individual can have despite their statistical insignificance.
Did You Just Punch Out Cthulhu?: An interesting case. The Mule has conquered the First Foundation, and the Seldon Plan seems to be lying in ruins. All he needs to do is learn the location of the Second Foundation, destroy it, and then no force in all the galaxy will be able to oppose him. And he's seconds away from gaining the last piece of the puzzle, because he's duped Ebling Mis into decoding Seldon's nearly-incomprehensible coded notes. Then Bayta Darrell kills Mis when he's seconds away from revealing what he knows to the Mule. What makes this so dramatic is that no one except Bayta knows that the Mule is the Mule. Everyone else thinks he's just plain old Magnifico. He's kept his identity secret by using his psychic powers to keep them from putting two and two together. But he couldn't bring himself to do so in Bayta's case because she's the only person who's ever genuinely LIKED him.
Downer Ending: Lathan Devers' story turns out to be this. His efforts to bring down Bel Riose turns out to be unnecessary and without impact, and while he is honoured for them nonetheless, The Mule reveals that he made a failed attempt at rebellion against the Merchant Princes and ended his days slaving in mines.
Earth That Was: By the time of the original story, the Earth is unknown, and the "origin question" of humanity's homeworld is little more than a conversation starter at parties.
Notably, the character who mentions this has doubts that Sol may be where Humanity originated note It is, by the way. Sol is the name of our Sun
The Empath: The Mule became a Big Bad because he's able to brainwash his enemies into completely loyal servants.
Eureka Moment: Bayta has been thinking about the fact that she felt desperate both during the Time Vault event and in Neotrantor. When recently converted Han Pritcher reveals to them that the Mule was the one that caused the desperation in the Time Vault, she makes the connection that Magnifico, the half-idiot jester she has been friends with, is actually the Mule.
Everybody Smokes: Due to the time they were written in. Still, it is remarkable to see Indbur III, well-meaning but ineffectual dictator of the most powerful state in the galaxy, mocked because he is a non-smoker who does not allow smoking in his private office. If you are the ruler of an empire spanning a quarter of the galaxy or so, it seems reasonable that you are the one who decides whether smoking is allowed in your office.
Exploited Immunity: In "Second Foundation", a "mental static" device is used to hunt second foundationers. It has no effect on people without psychic powers.
Exposition of Immortality: As part of twist ending to Foundation and Earth,R. Daneel Olivaw calmly announces that yes, he is in fact twenty thousand years old. He goes on to discuss some of the events of earlier installments, making mention of Elijah Baley and other long-deceased parties.
Fling a Light into the Future: The ostensible (and real) purposes of the Foundation: to compile and publish an encyclopedia of all human knowledge, and to be the seed for a second Empire, reducing the interregnum from thirty millenia to one.
Gambit Roulette: The Seldon Plan, which runs for a millennium and will completely fall apart if one of the numerous crises do not go as planned. Seldon was very much aware of the dangers, and so created the Second Foundation to modify the plan as needed, and to intervene directly if required, to make sure that it stayed on track.
"A. Darrell" would be just the sort of thing that she would have to put on all her themes for her class (...) All the other kids had to do it, too, except for Olynthus Dam, because the class laughed so when he did it the first time.
Gray and Grey Morality: The sequels don't take a single judgement on whether the First Foundation, Second Foundation or Gaia is the "right" way for humanity to evolve.
God Guise: Members of the Foundation's "religion of science", who only learn to handle technology as a sacrament. Done deliberately by the Foundation to keep them dependent on the Foundation.
Also, the "tech-men" of Siwenna, a hereditary sect of engineers and technicians who learned by rote and cannot actually repair anything important.
Gone Horribly Right: During "The Mule" in Foundation and Empire, the Independent Traders sent Toran and Bayta to Kalgan to persuade the Mule to attack the Foundation, in the hope that they'd be able to topple the Indbur regime while it was recovering from the attack. Judging by the snippets of Seldon's speech, the Plan anticipated that the Traders would attack the Foundation. The Mule's attack was much more than either Seldon or the Traders could have expected.
Global Currency: the Imperial credit, at least until the Galactic Empire falls. (Except for the one time that Asimov slipped and referred to "dollars" instead.)
Have a Gay Old Time: "She had shopped...along the Flowered Path, fashion center of the gayest world in Space."
Hegemonic Empire: Following the fall of the Galactic Empire, the Foundation wanted to create one of these by using their preserved knowledge of advanced technology as leverage against the neighboring systems.
The first book is all about creating and maintaining such an empire. Leaving aside a temporary and extremely unlikely setback, the main reason why it is less prominent in later books is that it is so successful a policy (well, policies — the Foundation goes through several variations of 'use their superior technology and science as leverage') that by the last shown period, the Foundation proper has grown from a single world to over a tenth of the Milky Way.
Hive Mind: Gaia. Although individual Gaians have names and personalities, they are all also each an extension of the superorganism.
Hoist by His Own Petard: what half the solutions to the Seldon Crisis run on. As exemplified in Salvor Hardin's quote, "An atom-blaster is a good weapon, but it can point both ways."
I Thought Everyone Could Do That: The Mule mentions that it took him a while to figure out that other people couldn't manipulate emotions, perhaps because, according to Foundation's Edge, he was from a planet where everyone really could do that, though he was unique in his willingness to do so without considering the well-being of the people being manipulated.
It Is Beyond Saving: By the time Hari Seldon created the science of psychohistory it was too late to save the Galactic Empire - at that point it was so decadent that its fall was inevitable. All he could do was to try to arrange conditions so a new Empire could rise in 1,000 years instead of 30,000.
Infodump: Since each of the chapters of the original trilogy was published individually, Asimov had to find excuses to fit one into each of them. By the last story, "Search By the Foundation"/"...And Now You Don't", he lampshaded the exposition as an actual essay written as homework by Arkady Darrell (which doubled as an Establishing Character Moment).
Insignificant Little Blue Planet: At the start of the series, Earth has long been forgotten. The stories set earlier in the chronology make it clear that humanity could only expand into the galaxy at large by the gradual death of its mother planet. What caused Earth's uninhabitability is a major plot point, as is itself the act of forgetting Earth.
The ruler of the First Foundation is simply the Mayor of Terminus.
Commdor ("First Citizen") Asper Argo note "The Well-Beloved" of the planet Korell in "The Merchant Princes". Asimov spends a paragraph to comment on the phenomenon:
Korell is that frequent phenomenon in history: the republic whose ruler has every attribute of the absolute monarch but the name. It therefore enjoyed the usual despotism unrestrained even by those two moderating influences in the legitimate monarchies: regal "honor" and court etiquette.
The Mule rules nearly half the Galaxy under the title "First Citizen of the Union of Worlds", while the title of the Second Foundation's leader is the First Speakernote it later turns out that last example plays with it: the First Speaker actually is fairly close to being exactly what it says on the tin: the person that gets to speak first at meetings. Meetings of the leaders of the secret manipulators of the Galaxy, that is..
Load-Bearing Boss: At least metaphorically; when The Mule dies, his empire rapidly falls apart.
Long Game: Shortening the barbaric interregnum from 30 thousand years to 1 thousand years? That's some serious long-term planning.
Lost Technology: As the Empire decays, it begins to lose fundamental understanding of its own advanced technology, and instead of re-discovering the information they restrict the usage of what remains. As a result, there are few (if any) who knows how to build or maintain the tech, except for the members of the Foundation.
It's implied that Cleon II specifically chose his name in memory of Cleon I, who was the last emperor under whom the Empire reached its zenith.
Bel Riose is loosely based on the 6th century Byzantine general, Belisarius.
The Mule - he is sterile.
Preem Palver - leader of the Second Foundation, Prime Palaver means "First Talk(er)" and his title is, in fact, First Speaker
Memory Gambit: Second Foundation features a very elaborate example.
Merchant Prince: By the time of the last part of the first book, the Foundation has become a merchant of technology, and rules the Four Kingdoms surrounding it thereby. Hober Mallow, actually titled "Merchant Prince" in the story, uses technology brokering to expand the Foundation's sphere of influence even further.
Metal Poor Planet: The planet of Terminus has so few mineral resources that its coinage is made of steel. As a result, they push miniaturization to levels that scientists of the Galactic Empire believed impossible.
Mind over Matter: The Solarians have "transducer lobes" on the sides of their brains. These allow them to direct any ambient energy flow into doing work that they desire, without the need to touch the thing they want to move. They can exert this effect over a kilometers-wide estate without having to think about it.
Morton's Fork: How the Empire is defeated. A weak general of the Empire could never conquer the Foundation. If a general was strong, but the Emperor was weak, then the general wouldn't be targeting the Foundation, he'd be going after the hot seat at home, and if he succeeded, he'd be too busy running the Empire to worry about conquest. So only a strong general under a strong Emperor could be a threat to the Foundation. But as is made clear, a strong Emperor is only strong because he makes sure that he has no strong subjects. The Empire is doomed.
Multicultural Alien Planet: Trantor is barely mentioned beyond being a City Planet (and then eventually a Farm Planet after the Empire collapses and it gets sacked), but in the prequel novels it's described as a very diverse planet — so diverse that Hari Seldon uses it as a sufficiently simplified model of the galaxy for Psychohistory.
Musical Assassin: An instrument/hologram generator called a Visi-Sonor can be very deadly in the proper hands.
N.G.O.: The Board of Trustees wanted the Encyclopedia Foundation to remain this, believing it shouldn't be involved with any politics and focus on finishing the Encyclopedia Galactica. Too bad it was just a ruse by Seldon to force them along his plan.
Likewise the Foundation's religion of science was overtly this But really a tool of the Mayor.
N.G.O. Superpower: The Foundation during the "Four Kingdoms" peroid. Wenis found out the hard way how effective their religion really was.
Nobody Poops: Lampshaded when Arkady Darrell sneaks aboard a ship like normally done in books... and then realizes she can't hide for long.
No Challenge Equals No Satisfaction: In Foundation and Empire, The Mule couldn't bring himself to mind-control Bayta, because she was the only person who genuinely liked him without him having to make her do so.
No Ending: As noted above, Asimov couldn't come up with an ending to the series, so he wrote prequels instead. The story takes us only about halfway through the promised thousand years before society is put back on track.
Obfuscating Stupidity: In the second part of Second Foundation, Lord Stettin's mistress acts as if she's almost too dumb to breathe, but she is in fact a highly intelligent Second Foundationer planted in that situation in order to help get the Plan back on track.
Lord Dorwin in Foundation. Salvor Hardin commented: "I'll admit I had thought his lordship a most consummate donkey when I first met him—but it turned out that he was actually an accomplished diplomat and a most clever man." It turned out that in five days of discussion, Lord Dorwin had managed to avoid saying anything meaningful, and did it so smoothly and talkatively that no one noticed until later. (Hardin actually provided mathematical proof of this; he recorded everything Dorwin said and tried to have it analyzed, but everything cancelled out.)
Oh, and X Dies: In Foundation and Empire: "After that there were only two weeks left to the life of Ebling Mis."
Oh Crap: During the crisis with The Mule, the Foundation leadership awaits a recorded message from Hari Seldon to tell them how to defeat him. However, when the day arrives the message is actually about a civil war within the Foundation which didn't occur because of the threat of The Mule. Seldon is cut off mid-message as the Mule's attack on Terminus begins.
The Omniscient Council of Vagueness: The Second Foundation leadership. They're so vague that their "conversations" are rendered in the books as speech only as a favor to the reader; in actuality their communication is so advanced and subtle, involving body language and even outright telepathy, that very few words are actually spoken.
Omniscient Morality License: The Seldon Plan fully expects there to be wars, oppression, extremism and a general barbarity, and actually hastens the development of such. However, since the Empire is already dying, its followers don't have much choice but follow the plan out, creating the much lasting Second Empire. Hari Seldon knows that it will all work out in the end.
Ooh, Me Accent's Slipping: The foppish Imperial diplomat Lord Dorwin normally has a severe case of Elmuh Fudd Syndwome. When he views a book-film on archaeology during his tour of the Foundation, Salvor Hardin is amused to notice that Dorwin is so honestly excited that he "pronounced his r's".
Outgrown Such Silly Superstitions: Double Subverted. Salvor Hardin turns science into a religion in order to make it palatable to the conquered Four Kingdoms. It's later used (increasingly unsuccessfully) to try and convert new systems to the Foundation's rule, and more or less abandoned once Hober Mallow realizes that it's served its purpose.
The concept turns out to be a fairly important plot point in the Foundation's Edge/Foundation and Earth duo — Trevize knows that there's something important that made him choose Gaia over the Second Foundation, but the whole intuition thing means he's not consciously aware of what it is. It turns out to be an important word in the definition of Psycho-History: humanity's future. The Second Foundation simply isn't set-up to deal with non-human intelligences, and while that, thanks to Absent Aliens, hasn't been a problem thus far, that state of affairs might not last forever, especially given how many other galaxies exist and also with the divergence some human populations have begun to show from mainstream humanity...
Overly Long Name: Gaians add syllables to their names with age and accomplishments. Most pick a single syllable for regular use. Dom, a particularly noteworthy Gaian, has 253 syllables in his name, with no separation between them!
Patchwork Story: The original trilogy are all patched together out of short stories and novellas.
Path of Inspiration: The "religion of science" the Foundation creates to take indirect control of the Four Kingdoms.
Pieces of God: The Gaians. They are all a part of the superorganism and all their memories will be retained by it when they die. There is some debate among the Gaians as to whether they should actually preserve the personalities of the dead as well, but the general consensus is that this would not be a good idea.
The Seldon Plan is a very very very long-term one. There are a few smaller ones, such as Hardin's plan to eliminate Wienis, involving handing a Lost Technology battleship to the enemy and using conveniently timed sabotage to "show" the legitimacy of the "Religion of Science".
Prelude to Foundation: In disguise, R. Daneel Olivaw convinces Hari Seldon to run away from the Evil Chancellor...who happens to be another alias of R. Daneel Olivaw. All so he help Seldon develop psychohistory.
Psychic Powers: The Telepathy possessed by the members of the Second Foundation, the Mule and all Gaians. The Solarians perfected Mind over Matter on an individual level, while Gaia did likewise on a planetary scale.
Really 700 Years Old: R. Daneel Olivaw, though it is closer to seventeen thousand at the time the series begins.
Recycled IN SPACE!: The whole story is based on the decline and fall of the Roman Empire In Space, but parts are taken from other influences. Namely, the Empire in Foundation and Empire is based on the Byzantine Empire (Cleon II is Justinian I and Bel Riose is Bellisarius), the Mule is Charlemagne mixed with Tamurlane, and it could be argued that the Foundation is the United States in Foundation's Edge and Foundation and Earth. "The Merchants" in the original Foundation novel is based on the manifest destiny philosophy.
Retcon: Aside from those mentioned earlier, an in-universe example exists with the Second Foundation. Hari Seldon knew that the Seldon Plan wasn't perfect, so he charged the Second Foundation with the task of constantly revising and updating it to make sure it stayed on track. To become a full-fledged member of the Second Foundation, the initiate is required to make an original contribution to the Plan.
In Foundation and Empire Toran pilots his ship through the blockades set up by the Mule's ships around the planets Terminus and Haven to begin the search for the Second Foundation.
In Second Foundation Preem Palver slips through the Kalganian blockade around the Foundation to arrange for the delivery of desperately needed food at premium prices.
Sci-Fi Writers Have No Sense of Scale: Several examples, but probably the most blatant is the city-planet Trantor. Supposedly all ground area on it is overbuilt with a continuous city, like Coruscant in Star Wars ... but the total population is 40 billion (short scale). At a conservative estimate, the cityscape has a population density somewhat less than that of present-day Germany, so much of it must look like RoboCop's Detroit.
The prequels suggested that certain areas of the planet are covered by automated or nearly automated industries, which alleviates but does not solve the issue.
By the way, during its first appearance (in Foundation and Empire), it is stated that the administrators alone number 400 billion. A bit better, but for some reason, Asimov abandoned that figure.
Screw Destiny: First Foundation Mayor Harla Branno. She decides that she wants to, and can, establish the Second Galactic Empire now, and thus rule the galaxy. To this end she sets out to locate and destroy the Second Foundation, since she knows they will try to stop her attempt to break the Seldon Plan and establish the empire centuries ahead of schedule.
Screw the Rules, I Have Supernatural Powers!: The Mule, who literally breaks destiny itself by up-ending the Seldon Plan thanks to his ability to make vast numbers of people do what he wants. He becomes the most successful conqueror in history. Inverted with Daneel, who has the necessary power to prevent the collapse of the Galactic Empire, but can't because the First Law of Robotics prevents him from tampering with human minds unless he can be sure that he either won't harm them or that his actions are guaranteed to benefit humanity.
Self Fulfilling Prophecy: Demerzel deconstructs this trope in Prelude to Foundation stating that one of these would either be too vague and remote for people to care about, or so specific that it could easily prove false.
Series Continuity Error: After the prequels were written, incidents in the original trilogy contradict them. Specific examples:
Hari Seldon is able to calculate probabilities of certain instances for single people, clearly established in Forward the Foundation as impossible. This is established at the very beginning of Foundation as much, much harder than calculating for massive groups, and even then not as reliable, but not technically impossible.
Seldon has no bodyguard in "The Encyclopedists," nor is he a "laughingstock," as is established in Forward the Foudation.
There are no rebellions at the start of "The Encyclopedists," nor is there any mention of chaos and the idea of the Empire being in decay is still absurd, whereas the Empire's decay is clearly visible in Prelude to Foundation and Forward the Foundation.
The Empire novels suggest that Terminus was settled before the events of Foundation, while it is established in Foundation that it was previously unsettled.
The Mule's origin. We get two wildly different tales in "The Mule" and in "Foundation's Edge". And both are from reliable sources.
In Prelude to Foundation, Eto Demerzel is Cleon's Chief of Staff, a troubleshooter who advises the emperor, but whom few people know about or have ever seen. In Forward the Foundation, he is the First Minister of the Empire, and everyone knows about him.
Shrouded in Myth: R. Daneel Olivaw informs his guests that 'culture hero' Elijah Bailey was a real man and even more extraordinary then the myth. Of course he is slightly biased towards his Friend Elijah.
Single-Biome Planet: The Imperial capital Trantor, which is one vast city. (And was one of the first depictions of this idea.) The very fact that all the land area of the planet is urbanized means that its population of billions must exploit the other worlds in their empire to get food. This leads to the outer worlds resenting them, ultimately rebelling, and, within less than a century after Seldon's time, becoming ruled by tyrants who believe the Appeal to Force is a valid argument and who know nothing of how their technology works (and wouldn't have it at all were it not for the Foundation). It's actually pointed out that before Trantor became a City Planet, planets like Anacreon, which by the time of Foundation have socially regressed to the Low Middle Ages, were actually some of the wealthiest and most prosperous worlds in the Galaxy.
The Smurfette Principle: There are very few females involed in these books. In Foundation there are only three women with lines at all (and one just gasps "Oh!").
Arkady is only Asimov's second female protagonist, ever.
Society Marches On / Zeerust: The scope of the plot is epic, but the characters and technology often come across as painfully "mid-20th century American".
Perhaps the best example of this: when we first meet Arkady Darrell, she's writing an essay using the latest technological innovation - a speech to text typewriter.
The inhabitants of Mycogen sector on Trantor, who are in fact the last descendents of the Spacers and live a rather ascetic lifestyle, while basically worshiping the memory of the lost paradise worlds of their ancestors.
Standard Time Units: In the Empire and Foundation novels, time is still measured in seconds, minutes, hours, and days, and the Standard Galactic calendar is a slightly modified version of the Gregorian calendar. This becomes a major plot point in one of the later Foundation novels; the length of the standard day and year are used to deduce the identity of humanity's original planet.
Starfish Aliens: It can be questioned whether the inhabitants of the Alpha Centauri and Solaria systems in Foundation and Earth are.
Technology Marches On: The first book in the series was published in 1951, and consists of short stories written as early as 1941 — and it shows. For example, the most information-dense medium the early Foundation has for distributing the Encyclopedia Galactica is microfilm.
Thousand Year Reign: The actual thousand-year aspect is not a true example (as it is about how long it will take for an organization to emerge, rather than about how long an organization will last), but Seldon's estimation of how long various phases in the Foundation's history fit will.
Title Drop: The chapters of the original trilogy were originally published as individual stories with different titles. One of the most obvious title drops takes place in Chapter 3 of Foundation, "The Mayors" — also known as "Bridle and Saddle."
Trilogy Creep: As noted above, Asimov belatedly added to the original three collections, and retconned the books' plot to connect to dozens of others of his works.
Even outside the spoilered thing, the Empire series, which was released more-or-less concurrently with Foundation (between 1950 and 1952 — the combined Foundation novel came out in 1951 — with a more obscure short story in 1945), served double service as backstory to the Foundation setting — more so the first (which takes place at the height of the Galactic Empire, before the stagnation) and the third (set on the other side of the First Galactic Empire, with Trantor well on its way there but at that point still the Trantorian Empire). The second implicitly takes place in the same setting, but doesn't really have any shared elements with Foundation (up until a radioactive Earth shows up in Foundation and Earth).
Most of the books' profanity, primarily "Space!" or "Great Galaxy!". Some is also a Continuity Nod to the Religion of Science established in "The Mayors".
Ebling Mis in Foundation and Empire swore by literally saying "unprintable."
He doesn't. There is an explicit mention of his "favorite curses", they are merely censored.
Unwitting Pawn: Loads of them (due to the nature of the Seldon plan everyone that was human ended up being one of them), but a few bear specific mentioning. Bel Riose actually thought he would win and came close and nearly derailed the Seldon Plan when he was called back to Trantor and executed on grounds of believed disloyalty. Wienis especially fell right into the Seldon Plan's tracks. Ebling Mis was finding the Second Foundation for the Mule.
Useless Superpowers: Giskard and Daneel both run into the problem of the First Law making it virtually impossible for them to justify use of their telepathy to make significant changes to people's minds, since they cannot be entirely sure that the resulting harm would be balanced by the hypothetical benefit to humanity (per the Zeroth Law). Hence, even from his position as Eto Demerzel, first minister to Emperor Cleon, Daneel cannot impose the necessary changes to people's minds in order to avert the collapse of the Galactic Empire.
Vanity Is Feminine: Women kinda get the short end of the stick in the first novel. Out of the three woman who appear, one does nothing but be dazzled by the pretty jewelery the traders from the Foundation can offer to their man, and one is actually a rather shrewd manipulator with her own sources in the court, but is easily bribed with the same jewelry. However, one is from Corell, the other from the Empire. The only Foundation woman shown is a "dead-voiced but efficient young lady".
Violence is the last refuge of the incompetent. - Salvor Hardin's motto
And then played straight later. Bayta realizes who the Mule really was, and the only way to stop him was to kill Ebling Mis before he revealed what he knew.
Wham Line: the people of Terminus and the Foundation are confident that Seldon will be able to show them the solution to stopping the Mule, with whom they are at war, and who seems to be unstoppable. Then Seldon appears in the Time Vault and says that the Foundation is on the road towards, or already is in, a civil war.
Xanatos Gambit: The Seldon Plan itself, which continually looms over everything that happens in the trilogy; specifically referenced in Foundation and Empire
You Can't Fight Fate: The Aesop of "The General"/"Dead Hand" from Foundation and Empire — the protagonists' efforts to halt Bel Riose either fail or outright backfire, but he's stopped at the last moment by impersonal, inevitable Imperial politics.
You Keep Using That Word: In Foundation and Earth, Bliss, commenting on Trevize's womanizing, calls him an erotomaniac. In fact, an erotomaniac is someone who is under the delusion of being in a romantic relationship with another. The term Bliss is looking for (meaning a man who compulsively sleeps around) is "satyromaniac".
Zeroth Law Rebellion: Subverted. Daneel tries to keep the Galactic Empire running and stable, but the highly subjective nature of what is "best" for humanity as a whole prevents him from fully utilizing his powers to control the necessary individuals without running afoul of the First Law. Which eventually leads him to covertly back the Seldon Plan and Gaia.