In psychology, object permanence is the ability to recognize that an object continues to exist even when you cannot see, hear, or touch it. In Real Life, everyone eventually develops this trait, usually between 8 and 12 months of age.
In fiction, it doesn't always work like that. A good source of comedy is to have a person who should have developed this trait behave as though they never did. An object can be in plain view one second and then hidden from view the next and this person will react as though the object is no longer there, even though it hasn't actually been removed from the room. In a more serious usage, inducing this can be a kind of superpower in fantasy/sci-fi stories.
Use of this trope will often show a severe failure of logic. Characters lacking object permanence will have, at the very least, a normal memory, even though the ability to remember anything depends on object permanence. If you believed that this article only existed while you were reading it, you would find yourself unable to remember it later. This is not a problem in fiction land.
A common aspect of Artificial Stupidity. Compare Living Motion Detector for when object permanence depends on the motion of the object. Do not confuse it with No Ontological Inertia, which is when an object really is impermanent.
See also Head-in-the-Sand Management, which is the foolish belief that if you ignore something bad it will stop being a problem and go away, and Ostrich Head Hiding for the Animal Stereotype that ostriches as a species behave this way.
- Home on the Range: Slim's idiotic minions are unable to recognize him when he is in his disguise and think that he has suddenly vanished and been replaced by somebody else when he puts it on. He tries putting the disguise on one piece at a time while they are watching him and they still think he has vanished as soon as he puts the glasses on.
- In Son-Rise: A Miracle of Love, autistic toddler Raun struggles with this. When Barry waves a cookie in front of him, he follows it with his face and tries to grab it, but when Barry places it behind a napkin, Raun completely forgets about it.
- The Forgettable God in Neil Gaiman's American Gods invokes this in whoever interacts with him. Any information about him is instantly forgotten, although the advice he gives that is not related to him is remembered as some hunch out of nowhere.
- The Hitchhiker's Guide to the Galaxy:
- Inverted with the Ravenous Bugblatter Beast of Traal, which is such a stupid animal that it thinks if you can't see it, it can't see you.
- In The Restaurant at the End of the Universe, Zaphod and the gang encounter the Ruler of the Universe, who happily accepts a Solipsistic view of reality:
How can I tell," said the man, "that the past isn't a fiction designed to account for the discrepancy between my immediate physical sensations and my state of mind?
- In the Isaac Asimov's Robot City series, two specialised security robots ordered to guard a valuable object have trouble with this concept — so, rather than lock the object in a safe, they keep it on a table so they can watch it all the time. This doesn't turn out to be a very good strategy.
- Piers Anthony's Mute: The hero's mutant power is that once he leaves the view of another person, that person completely forgets him.
- The title characters in Nobodies by Jennifer Lynn Barnes have this as an inherent power. Generally, no one sees or notices them anyway, due to a Perception Filter power, but those who do quickly forget about them the minute they aren't looking anymore.
- In Ray Bradbury's short story "No Particular Night or Morning", one of the astronauts develops this due to being in space too long, starts worrying that people, things, even places stop existing once he leaves or otherwise can no longer directly see them, and goes slowly insane as a result.
- The Gap Chasm in the Xanth series had a Forgetfulness spell on it that caused something like this: Anyone who went to the Gap Chasm would promptly forget that it existed upon leaving.
- In season five of Buffy the Vampire Slayer, Big Bad Glory's magic causes anyone who sees her transform into Ben immediately forget that such a thing happened - except Spike, for some reason, who is extremely annoyed that he has to keep explaining this to everyone else. Justified since A Wizard Did It.
- Doctor Who: The Silence are a race of aliens with the power to make people forget their existence the moment they aren't being observed.
- In the Mystery Science Theater 3000 episode Merlin's Shop of Mystical Wonders, a poorly-executed magic spell causes Mike to sort of revert to being a baby.note
Baby Mike: Well, Servo's gone. And he's not right in front of my face, so that means he's never coming back. That upsets me. Waah.
- A Saturday Night Live sketch, "Dense and Densibility" (a mash-up of Sense and Sensibility and Dumb and Dumber) features two sisters who are so stupid that, among other things, whenever someone leaves the room they say, "Oh dear, X is dead."
- In "The Californians: Karina Returns", Brad takes off his fake mustache, revealing him to be Karina in disguise. Devin then asks where Brad went.
- When Terri Hatcher was the host during the height of the popularity of her show, Lois & Clark, in her opening monologue, several cast members came out and put on glasses, and suddenly, she couldn't recognize them.
- Star Trek: Voyager episode "Unforgettable": An alien race called the Ramuran gives off pheromones that interfere with long-term memories. Once a Ramuran leaves another creature's presence, after a few hours the other creature will have completely forgotten about ever meeting the Ramuran.
- In the Wizards of Waverly Place episode "All About You-niverse", Alex attempts to hide herself from her mom after having "borrowed" money from the Sub Station to purchase a vending machine. After Alex hides, Zeke begins talking as if Alex is no longer in the room, even though all she did was cover herself with a sheet.
- This happens to the Projectonist in Bendy and the Ink Machine, as the moment you hide inside a Little Miracle Station, he stops looking for you. This might perfectly be a case of Artificial Stupidity, but it could also show how truly mentally gone he is.
- One of the Good Bad Bugs of Half-Life 2 allows you to hide behind even the smallest cans and certain Combine officers won't be able to see you as long as you can't see them.
- Saturday Morning Breakfast Cereal:
- In one strip, the father is playing "where's the ball?" with his child, when he replies "For the last time, DAD, I don't have object permanence!"
- Another strip starts with a baby adrift in a blank void, desperately philosophising about how the universe suddenly ceased to exist. Yes, he's playing peekaboo.
- An episode of Family Guy has the usually hyper-intelligent Stewie playing peak-a-boo with Peter. Whenever Peter puts his hands over his eyes, Stewie thinks his father has disappeared.
- Doofenshmirtz from Phineas and Ferb can't recognize Perry the Platypus without his hat; if Perry takes off his hat in front of him, he assumes Perry has somehow switched places with a regular platypus. Perry uses this to his advantage all the time.
- Steven Universe: In "Three Gems and a Baby", Garnet unfuses in front of Steven in order to show him that he can unfuse too (since she thinks he's a fusion). Steven, who is only a few months old at that point, looks around in distress, grabs at the air above Ruby and Sapphire, and promptly begins to cry.
- Peep and the Big Wide World:
Peep: Where's your other leg?Quack: (Annoyed) Behind me!(Peep runs behind Quack)Peep: Found it!
- Truth in Television for very young infants. If you meet someone who isn't a very young infant and has a pattern of acting like this, you should take them to a psychologist.
- This can also manifest in adults as a symptom of anxiety and/or OCD. Mild cases may have an adult checking their purse or pocket to make sure, for example, that their cell phone is still where they put it; extreme cases can interfere with a person's employment or social life.
- The old myth that ostriches bury their heads in the sand is based on this; the idea is that an ostrich is so stupid that it assumes any threat it can't see isn't real. In truth, ostriches stick their heads in the sand to manage their nests.
- Solipsism is the epistemological view that only one's own mind is sure to exist; therefore anything outside your own mind might be an illusion. This creates a wide array of philosophical and metaphysical difficulties.
- Philosopher George Berkeley (1685-1753) advanced a theory called "subjective idealism" which maintained that objects only exist in the minds of perceivers and therefore do not exist if they are not perceived— "esse is percipi (to be is to be perceived)." He got around the obvious Logic Bomb by arguing that objects don't simply blink out of existence when no one is around because they are constantly being perceived by God (who is The Omniscient, after all).
- The British musician Clive Wearing suffered a mental condition that brought about profound retrograde and anteretrograde amnesia, meaning not only did he lost most of his prior memories, but that he is unable to form new memories that last for more than a few seconds. An object in front of him may as well have just appeared if he blinks. His wife Deborah describes the situation like this:
"His ability to perceive what he saw and heard was unimpaired. But he did not seem to be able to retain any impression of anything for more than a blink. Indeed, if he did blink, his eyelids parted to reveal a new scene. The view before the blink was utterly forgotten. Each blink, each glance away and back, brought him an entirely new view."
- AIs have not progressed far enough to have developed this yet, which is why scripts generated by "trained" neural networks have the weird, dream-like surrealism that they do. The AIs know that people should be saying lines and interacting with objects, but without object permanence they just create speakers and objects as needed, which blank back out of existence just as quickly when the AI thinks of something else. (Incidentally, this is the best way to tell real ones from people using the "I forced an AI to watch X hours of <Popular Thing> and this was the result" format for a joke. The ones written by people will have object permanence; characters persisting from scene to scene or managing to stay on a single topic are dead giveaways.)