Solipsism is a philosophical belief that only one's mind is certain to exist.

You, reading this: Think, right now. No, just think. By thinking, you have confirmed Rene Descartes' immortal postulate--"I think, therefore I am"--and proved that you exist. Now, can you prove that anything else around you exists?

Let's start with the digital screen upon which you are probably reading this treatise. Can you prove it exists? You might say, "I am seeing it, therefore it exists..." But what you are seeing is not necessarily what is actually there. Your eyes perceive light and convert that perception into nerve impulses, which are then compiled by your brain into some sort of visual picture. With all these translations going on, are you ''sure'' that what your brain perceives is actually there? It is very accurate to say that the computer screen is projecting something which your brain ''perceives'' to be text, but you cannot, with your eyes alone, prove that the computer screen is ''actually'' projecting text.

And here's the scary thing: ''neither can anybody else''. Even if you ask your friend to come over and confirm the existence of the thing, the problem is that his or her eyes and nerves are just as fallible, just as untrustworthy, as yours. In other words, while the two of you can largely agree on the mass hallucination you call "a computer screen," it still ''is'' a mass hallucination. Maybe the computer screen is projecting something entirely different. Maybe what we call "blue" is actually orange. Maybe the computer screen ''isn't'' there. Something must ''be'' there, to create the physical phenomena we call "computer screen," but there is nothing to guarantee that said thing is anything like what we call a computer screen... or, indeed, is anything like anything at all. Heck, maybe it ''isn't'' there! We still can't verify the thing's qualities; how can we possibly verify its existence?? It may actually exist--it ''probably'' exists; otherwise the fact that we are seeing the contents of a TVTropes UsefulNotes page printed on thin air says something rather unflattering about our SanityMeter--but we cannot '''prove''' it.

And let's take it a step farther: now that you've asked your friend to prove that the computer screen exists, [[MindScrew can you prove that]] ''[[MindScrew s/he]]'' [[MindScrew exists]]? After all, your eyes and nerves are still just as fallible as they were when staring at that alleged computer screen...

Ladies and gentlemen: solipsism.

!!Epistemology, Metaphysics and Methodology - or, "Huh??"

Philosophy is a complicated beast, involving multiple branches, disciplines and areas of study. They include "Epistemology," the ''nature'' of knowledge, and "Metaphysics," contemplation of the fundamental nature of the world and those things in it. Epistemology asks, roughly, "What can we know, and how can we know it," while Metaphysics asks, "What, in the end, actually exists?--and, now that it exists, what is it like?"

This is being brought up because solipsism has application to both branches. You've already seen how in the explanation above; now we'll elaborate a bit more.

!!!Epistomological Solipsism

Solipsism was first proposed by a Greek philosopher, Gorgias, some time during the 400s or 300s BC. He stated, very simply:
#Nothing exists.
#Even if something exists, nothing can be known about it.
#Even if something could be known about it, knowledge about it can't be communicated to others.

What Gorgias had to say concerned TheTreacheryOfImages, writ large: we should be careful about what we (think we) see, and how much we trust our senses. TheOtherWiki has a very useful illustration:

-->If a person sets up a camera to photograph the moon when they are not looking at it, then at best they determine that there is an image of the moon in the camera when they eventually look at it. Logically, this does not assure that the moon itself (or even the camera) existed at the time the photograph is supposed to have been taken.

The end result is '''Epistomological Solipsism''': the belief that the only thing whose existence you can be ''certain'' of is your own mind, and mostly because you are thinking with it. The rest of the world ''may'' exist, but it might not, and even if it did you couldn't prove it. Descending from this is the idea of '''Methodological Solipsism''', the idea that, ''because'' you can only be certain of your own mind, that frame of reference needs to be the basis of all other conclusions.

!!!Metaphysical Solipsism

The most extreme version of solipsism, Metaphysical solipsism goes on to assert that, because we can't prove anything else exists, they therefore do not. Each of us might well be a BrainInAJar for all we can verify about the outside world. We are all living in a mass hallucination--or rather, ''I'' am living in one, since I can't verify your existence and therefore you don't. I am the [[LastOfHisKind last of my kind]].

In addition to being a rather bleak prospect to contemplate, this philosophy lacks evangelical oomph: why, after all, would I try to convince you that you don't exist? In addition to being rather insulting to you, the simple fact is that you ''don't'' exist--you're a figment of the mass ImagineSpot I've dreamed up to distract myself from being a BrainInAJar--and thus whether you believe in your own existence or not is just about the least relevant thing in the world. And even if I ''do'' succeed in converting you, [[ShaggyDogStory you still don't exist]], and my triumph cannot really be called meaningful.

Even worse, there are profound effects on one's view of morality. It doesn't change to [[BlackAndWhiteMorality Black And White]], or even [[BlueAndOrangeMorality Blue And Orange]]: ''it ceases to exist''. Murder, for instance, is typically described as the unlawful killing of another person-- ''What other person''? Surely it is not immoral to kill an ImaginaryFriend, who does not exist (and indeed, never existed) in the first place. The solipsist cannot cross the MoralEventHorizon because there is no one to condemn him or her for doing so. The end result is VideoGameCrueltyPotential played deadly straight.

!History

!Usage in Fiction
* Aten in ''TabletopGame/{{Scion}}'' is thoroughly convinced that nothing else in reality exists but as a fragment of his consciousness. As he's the avatar of a Greater Titan, this means he is effectively indestructible unless convinced he's ''not''. This extends to his goals - he wants everything that exists to worship him, and if that fails, he's willing to have his followers blow themselves up. He's also Akhenaten's only avatar, which helps to reinforce this view - he absorbed all of the others.
** There's also a Knack called Solipsistic Defense; once per scene, you can call on your Legend to render any one attack you didn't see coming harmless, simply by believing as hard as possible that it doesn't exist. As someone with the blood of a god, what you believe goes.
* The Solipsist class in ''TalesOfMajEyal'' is {{Exactly What It Says On The Tin}}, with abilities involving, among other things, creating matter from thoughts, distorting reality and disbelieving damage.
* Richard Ames, the main character of ''Literature/TheCatWhoWalksThroughWalls'' decides one morning to follow solipsism, and refers to other people (including his wife) as a figment of his imagination. Not a wholly straight example, as he's just doing it [[ItAmusedMe for his own amusement]].
* A racial class in the ''{{Tabletop/Rifts}}'' {{Sourcebook}} ''D-Bees of North America'' has metaphysical solipsism as their [[PlanetOfHats hat]]. Strangely, this is presented more of a Role-Playing quirk than anything else, as their philosophy does not turn them into amoral monsters.
* In ''Webcomic/{{Fans}}'', a {{Mad Scientist}}'s ray gun traps Marc in a dimension populated entirely by fractal copies of himself. Over the [[YearInsideHourOutside centuries]] that pass within "Marcworld," the occasional Marc-copy goes mad, believes he's the only one who really exists, and decides the only way to escape the CuckooNest is to kill all the "fake" fractal Marcs. ("Hold still, runts! This won't hurt, 'cause you don't exist!") This happens often enough that one or more Marcs become GenreSavvy and publish a pamphlet which refutes this metaphysical solipsism by pointing out that many others have come to the same conclusion, only to find that going on a "[[AxCrazy psycho rampage]]" doesn't, in fact, cause oneself to "wake up back in reality."
* Claire Stanfield of ''Anime/{{Baccano}}'' is a solipsist who claims that he can't die because everything is just a figment of his imagination and he can't imagine himself dying. Given that he's a both a friendly, likable, occasionally heroic guy and a brutal hitman who's tortured people and caused truly spectacular amounts of carnage, he's probably a prime example of the abovementioned effects that such a belief can have on your morality. He does have emotional attachments to other people but these seem to be somewhat akin to the attachments that people have to fictional characters, albeit somewhat stronger.
* The Party of ''Literature/NineteenEightyFour'' drives metaphysical solipsism to a particularly terrifying logical conclusion. O'Brien boasts that since nothing exists outside the consciousness, and the Party controls all information everywhere, the Party is like a collective RealityWarper that can distort and rewrite the past and even ''material reality itself''. Reality simply ''does not exist'' any more, the closest approximation is whatever the Party says is reality. And if you do not agree to their absurdity, they will use TwoPlusTortureMakesFive and MindRape until you believe it. Why, you ask? [[ForTheEvulz Because the Party wants nothing but power, and there is no greater power than inflicting misery and humiliation on other human beings]].