You Cannot Kill an Idea

""Kahless has been dead for a thousand years; but the idea of Kahless is still alive. Have you ever fought an idea, Picard? It has no weapon to destroy, no body to kill.""

- Gowron, Star Trek the Next Generation

What's the most resilient parasite? An idea. A single idea from the human mind can build cities. An idea can transform the world and rewrite all the rules. Armies and dictators have no power over them and while men can die, their ideas are immortal.

In fiction we get heroes dying but hope passed onto the audience by knowing that somehow his idea has lived on. Sometimes the hero is a martyr and his death is a beginning as people use it for inspiration; they are throwing off some kind of mind-breaking torture attempt to show that the forces of fascism can't control them. A book of philosophy or some diary may have survived him or one of his inner circle may tell his tale and so the story ends on a happy note, but not too happy. Our story is sad but the tide of inevitable revolution will come.

Super Trope of Can't Stop the Signal. The characters who pass on the idea are likely Doomed Moral Victors.

Anime

 * In One Piece, both Gold Rodger and Dr Hiriluk die embracing this ideal. Gold Rodger manages to start the Golden Age of Piracy.
 * In the face of a Marine Victory which could have snuffed out the Golden Age of Piracy, . The Marines were not happy with this.
 * Happens in Code Geass. Lelouch's ideals were to fight against injustice and tyranny caused largely by the Britannian Empire. Later, he causes changes in the empire itself, and in the end helps make the world a better place for almost everyone,

Comic Books
""Did you think to kill me? There's no flesh or blood within this cloak to kill. There's only an idea. Ideas are bulletproof.""
 * V for Vendetta: The anarchist title character, to Eric Finch, who's just shot him:

""The world will know that free men stood against a tyrant, that few stood against many and, before this battle is over, that even a god-king can bleed." (The ironic part is that, if Xerxes had followed through on his promised plans, the world wouldn't know of the Spartans last stand)"
 * In 300, Xerxes angrily declares that once he defeats the Spartans, he will completely destroy them and wipe out any trace of them from history. Leonidas coolly responds:

Film

 * In Casablanca, Victor Lazslo tries to assert this about La Résistance against the Nazis. The film itself does a good job of illustrating the concept. Unfortunately Those Wacky Nazis are an also an idea, and one that Victor Lazlo is kinda, you know, trying to kill.
 * Inception addresses this and emphasizes why it is so hard to plant one.
 * V for Vendetta had an epic one near the end. After taking dozens of bullets and killing a dozen men before they could finish reloading (as per his Badass Boast), V approaches The Dragon in Chief, who asks, in disbelief, "Why Won't You Die!" His response? "Beneath this mask is more than flesh; beneath this mask there is an idea, Mister Creedy -- and ideas. Are. Bulletproof."
 * Of course, the metal plate under his shirt helped.
 * Take it literally. The idea is to wear bullet-resistant plate when going to a gunfight.
 * Bruce Wayne uses this sort of reasoning when devising his future role in Batman Begins, as advised by Henri Ducard; a man acting just by himself as a man can be killed, bribed or discouraged, but by becoming a 'symbol' the man becomes "more than just a man"; even if he dies, the symbol lives on to inspire others. Guess what symbol Bruce eventually settles on...
 * Played with in Dogma where Rufus comments that "ideas" are malleable and can change and possibly even die out. "Beliefs," which are strengthened ideas, are much harder to even change, let alone kill. It also places a spin on it in that the fact that a belief is hard to 'kill' is not necessarily a good thing if the belief is not a good one, or if the belief has become an overly rigid dogma

Literature

 * Subverted in Nineteen Eighty Four, in an inversion of the inspirational "the hero lives on" type of endings:

More disturbingly, the entire concept of Newspeak is meant to defy this trope, by systematically eradicating even the words that could express ideas such as liberty, rebellion, or individuality, which run counter to the ideological orthodoxy of the Party.
 * Played for Laughs in Discworld novels on several occasions, frequently with people using rumors that once they get started can not be stopped. In Interesting Times, for instance, Rincewind goes around telling soldiers that in no way are there any invisible vampire ghosts about to attack them in the following battle and there are absolutely not 2,300,009 of them.
 * Of course Discworld takes it literally many times. Witches Abroad introduces the idea that on the Discworld, stories have not only memetic influence, but are a law of nature. In Soul Music and Moving Pictures, the immortal idea (rock music and movies, respectively) is the Big Bad.
 * In Thief of Time the Glass Clock, which destroyed all of history in the past, was removed from any books by the History Monks, but something that strong still seeped through and found its way into children's stories.
 * Belisarius Series: Used first seriously and then humorously. Belisarius starts a rumor about sexual prowess and general horniness of the Kushans in order to get Kungas and his men pulled away from their guard duty of a captured princess. Their incompetent replacements are easily dispatched and allow her to be rescued. Later, once the confused Kushans find out about the origin of the rumor, they then take delight in spreading it themselves.
 * The Dresden Files novella Backup goes into a bit of detail about The Oblivion War, a war waged, essentially, against ideas. Specifically, the memory of some unpleasant old gods who can't do anything if humans remain blissfully unaware of their existence. We don't get a lot of information, but since the antagonist is a cultist of said gods, and Thomas (the novella protagonist) mentioned the war has been ongoing for thousands of years, it fits.
 * In the Eighth Doctor Adventures, a group of Time Lords (the Celestis) take this concept literally, and convert themselves into ideas for this very reason. Unfortunately for them, a later book reveals that the Whoniverse also contains creatures which can kill -- and eat -- ideas.
 * The heavily associated spin-off Faction Paradox basically is this trope.
 * This is the crux of 's Thanatos Gambit in Mistborn. He purports himself as a figure of legend and a symbol of evolution, so that when he is killed, a vengeful religion rises up immediately to complete his work in his name.
 * In Fatherland (rephrased): "Cut a clearing in the forest of your mind, the trees are just waiting to reoccupy it."

Live-Action TV
""Kahless has been dead for a thousand years; but the idea of Kahless is still alive. Have you ever fought an idea, Picard? It has no weapon to destroy, no body to kill.""
 * Star Trek the Next Generation, "Rightful Heir": Chancellor Gowron talks about the symbolic effect of the return of the Klingon God Emperor.

""You can deny me all you want but you can't deny Ben Sisko – He exists! That future, that space station, all those people – they exist in here! In my mind. I created it. And everyone of you knew it, you read it. It's here. Do you hear what I'm telling you? You can pulp a story but you cannot destroy an idea, don't you understand, that's ancient knowledge, you cannot destroy an idea. That future – I created it, and it's real! Don't you understand? It is real. I created it. And it's real! It's real!""
 * Star Trek Deep Space Nine: "Far Beyond The Stars". Benjamin Sisko, dreaming that he's a science fiction writer in the 50s, reacts rather badly to having his story pulped because it has a black Captain.


 * Doctor Who: The Doctor was able to destroy a prime minister with this trope. He only needed to say six words to an aide. He doesn't die , and the PM isn't necessarily evil, but he does use the principle of an idea being unkillable.
 * At the climax of Babylon Five's Vorlon-Shadow War, Delenn and Sheridan point out that, even if they and their coalition are killed, their assertion that the younger races no longer need the First Ones is true. All the First Ones can do is subjugate them, not "teach" them as the two sides insist they want to.

Video Games
"Altaïr Ibn-La'Ahad ...how does one wage war against a concept? It is the perfect weapon. It lacks a physical form yet can alter the world around us in numerous, often violent ways. You cannot kill a creed. Even if you kill all of its adherents, destroy all of its writings – these are a reprieve at best. Some one, some day, will rediscover it. Reinvent it. I believe that even we, the Assassins, have simply re-discovered an Order that predates the Old Man himself..."
 * In Assassin's Creed II, one of the Codex pages reveals that Altaïr mused on this subject more than once, noting that the Templars waged war by seeking to win over the hearts and minds of people with ideas, rather than more conventional weapons. This made it rather difficult for the Assassins to fight back... But it also makes it rather difficult for the Templars to exterminate them.

"Sisteena: If you want to kill me, go ahead. I may die but my ideals will live on!"
 * Invoked in Deus Ex when the terrorist leader says 'You can't fight ideas with bullets'.
 * "A single artist, a single general, a single hero or a single villain may all die, but it is impossible to kill a people, a nation, an idea -- except when that idea has grown weak and is overpowered by one that is stronger." --The Doctrine of the Mighty
 * In Mad World, XIII says that he wants to see an idea die. A culture. A religion. Any idea.
 * The Illusive Man tries to pull this in Mass Effect 3...
 * Knights of the Old Republic: This is one of Kreia's favorite tropes. She points out that killing men is easier than killing belief and that Revan, in the process of fighting the Mandalorians, adopted Mandalorian tactics and their intolerance for the "weak." She also points out that every time the Jedi and Sith fight each other to near-extinction, the ideals of either side still remain as strong as ever, waiting for their chance to strike back in revenge and dooming the galaxy to endless warfare.
 * Tactics Ogre:

Webcomics

 * Remus Shepard had a go at this in Indefensible Positions, then deconstructed it in Genocide Man. The protagonist of the latter argues that an idea can be killed, and that some ideas should be killed--even if the only way to do so is to slaughter every single person who holds the idea.

Real Life
"I know you have come to kill. Kill me if you wish, coward, but know that you can only kill a man."
 * The Trope Namer is American civil rights activist Medgar Evers: "You can kill a man, but you can't kill an idea." He was later shot dead by a Klansman, but the civil rights movement endured.
 * Martyrs, like Jesus, are one of the reasons why Christianity flourished, since while Jesus himself died The Proto-Christian cultists who became The Remnant and the later Early Christians kept the ideology alive using the story of his life and his teachings until Emperor Constantine I attributed his victory in a battle to Christianity, which was the big turning point, albeit at the expense of pre-existing religions.
 * Che Guevara's last words, according to at least one biography:

"Ideas are more powerful than guns. We would not let our enemies have guns, why should we let them have ideas?"
 * There were several sects of early Christians that are only known about by official church writings condemning them. In some cases we only have the names and there must have been others where even that hasn't survived. Of course since we don't know what their ideas were it is impossible to say whether those ideas were killed, absorbed by the Catholic Church or recycled by better known groups.
 * "A man may die, nations may rise and fall, but an idea lives on. Ideas have endurance without death." -- John F Kennedy
 * Josef Stalin had a go:

"Cattle die, kinsmen die, we ourselves also die; but the fair fame never dies of him who has earned it."
 * Government propaganda targeted at an enemy intentionally invokes this trope, especially during wartime.
 * Opponents of the War On Terror and War On Drugs invoke this trope as one of their points. We shall not go any further.
 * Generally, outside attempts to forcibly repress or destroy an idea are doomed to fail, but ideas can destroy themselves if they inspire widespread revulsion and their practitioners are doing horrible things.
 * A legal punishment in ancient Rome was damnatio memoriae, which was an attempt to erase a political figure completely from history after his or her death. Their faces would be removed from portraits, statues damaged, and anything mentioning their name would be destroyed or erased. This is extremely difficult to pull off completely - for instance, we have some surviving busts of Publius Septimius Geta, denarii featuring his image, and a wealth of information about his personality, tastes, family politics and eventual assassination - and obviously it's impossible to know if a complete damnatio memoriae ever occurred.
 * A saying from the Norse Poetic Edda, attributed to Odin:


 * A similar saying is utilized in the Occupy protests, by the slogan "You cannot evict an idea".