What Is Solipsism? Why You Can’t Prove Anyone Else Exists

Last updated: November 4, 2026

Solipsism is the view that only your own mind is sure to exist, and in its strongest form the claim that nothing exists outside it at all: other people, the room you are sitting in and this sentence would then be contents of your consciousness and nothing more. The word comes from the Latin solus, “alone”, and ipse, “self”. Almost no philosopher has defended solipsism as true, yet it keeps coming back, because it is surprisingly hard to refute. Descartes ran into it, Wittgenstein tried to dissolve it, and today it returns as the brain in a vat, the simulation hypothesis and the NPC meme.

The meme above stages the whole debate with two faces. The crying Wojak delivers the solipsist’s argument almost word for word: all your perceptions could be lies, so the only thing you can accept as existing is your own mind. The calm Chad answers with the oldest reply in the book, that this is not how anyone actually sees the world. The joke is that both are partly right, and that the Wojak is, after all, shouting his argument at someone. That small contradiction, doubting that other minds exist and then trying to convince one of them, is exactly where the philosophical trouble with solipsism starts.

What Is Solipsism? The Meaning in One Sentence

Solipsism means that the self is all that can be known to exist, or, in its radical version, all that does exist. Everything else, from your best friend to the Andromeda galaxy, is either a doubtful hypothesis or simply a pattern in your own experience.

The Internet Encyclopedia of Philosophy, in Stephen P. Thornton’s entry, gives the most careful version. Solipsism, he writes, is “the doctrine that, in principle, ‘existence’ means for me my existence and that of my mental states.” The point is not just that you happen to be very self-centred. It is a claim about what words like “exist”, “world” and even “pain” can mean. As Thornton puts it, “the true solipsist understands the word ‘pain,’ for example, to mean ‘my pain.’” If you hear a friend groan after stubbing a toe, the solipsist has no way to treat that groan as evidence of another pain. There is only the sound, and the sound is part of your experience.

This is what separates solipsism from ordinary selfishness. A selfish person believes other people exist and simply does not care much about them. A solipsist, at least on paper, doubts that there is anyone there to care about. It also separates solipsism from the egoism of Max Stirner, which is sometimes confused with it. Stirner wanted to free the individual from what he called spooks, fixed ideas like duty and humanity, but he did not doubt that other people were real; if anything, they were his rivals. If you are curious about that very different kind of self-centredness, our post on Max Stirner’s spooks explains it.

Three Kinds of Solipsism: Metaphysical, Epistemological and Methodological

Philosophers distinguish at least three solipsisms, and most confusion about the word comes from mixing them up. The first is a wild claim about reality, the second a sober claim about knowledge, and the third a working rule in science.

Metaphysical solipsism is the radical version: only my mind exists. Epistemological solipsism is weaker and much harder to dismiss. In the Stanford Encyclopedia of Philosophy, Anita Avramides describes it as the view that “the only mind I can know is my own”, and she adds a conceptual variety, the claim that “the only mind I can think about is my own”. Methodological solipsism, finally, is not a belief about the world at all but a decision about how to study the mind, which we will come back to in the psychology section.

The distinction matters because the second and third kinds are respectable and the first is not. When people say solipsism is “irrefutable”, they usually mean the epistemological version: you cannot prove, with the certainty you have about your own thoughts, that anyone else has thoughts. That is a real problem, and philosophy has spent four centuries working on it. When they say solipsism is “absurd”, they usually mean the metaphysical version, and there they have a point.

Descartes, Berkeley and the Lonely Thinking Thing

Modern solipsism grows out of a method, not a belief. René Descartes did not want to be alone in the universe; he wanted certainty, and his method of doubting everything left him, for a while, with nothing but himself.

In the first of his Meditations, Descartes imagines an evil demon who deceives him about everything he sees and touches. In the second, he finds the one thing the demon cannot fake. In John Veitch’s translation: “I am, I exist, is necessarily true each time it is expressed by me, or conceived in my mind.” This is the famous cogito, which we unpack in I Think Therefore I Honk. The trouble is what the cogito leaves out. It proves that a thinker exists, and only one. Everyone else is still on the far side of the doubt.

Descartes noticed this himself in a striking passage of the same meditation. Looking down at people walking in the street, he asks: “what do I see from the window beyond hats and cloaks that might cover artificial machines, whose motions might be determined by springs?” His answer is that he does not see the people at all; he judges that they are there. “But I judge that there are human beings from these appearances”, he writes, by “the faculty of judgment alone which is in the mind.” It is a seventeenth century version of the question behind every NPC joke: how do you know the figures outside are not just very good machinery? Descartes eventually escapes by proving, to his own satisfaction, that a good God would not let him be deceived so thoroughly. Many readers have not found that exit convincing, which is why the door he opened has stayed open. His split between a thinking mind and an extended body, the subject of our post on Descartes’ mind-body dualism, made the gap between my mind and yours look even wider.

George Berkeley pushed the logic further and is often accused of solipsism as a result. In his Principles of Human Knowledge of 1710 he says of sensible things that “their esse is percipi”, their being is to be perceived, as the Project Gutenberg text renders it. A table exists because it is perceived, “or that some other spirit actually does perceive it”, as the Stanford Encyclopedia quotes him. That last clause is Berkeley’s safety rope. The world is not inside my mind alone; it persists in the mind of God and is shared with other spirits. Critics have objected that this only swaps my private world for God’s, but it shows that even the most radical idealist of the period worked hard not to end up alone. The wider battle between idealists and materialists is the subject of our post on materialism vs idealism.

The worry is not only a Western one. The Daoist classic Zhuangzi contains the story of the philosopher who dreams he is a butterfly and, on waking, cannot tell whether he is a man who dreamed of being a butterfly or a butterfly now dreaming that it is a man; a translation by Patrick Nowlin is online. Strictly speaking this is dream scepticism, not solipsism, since the butterfly and Zhuangzi are both still there. But it raises the same uncomfortable question about how far our ordinary certainty actually reaches.

The Problem of Other Minds: How Do You Know Anyone Is In There?

The serious core of solipsism is the problem of other minds: you experience your own thoughts directly, but you only ever see other people’s behaviour, so how do you know there is a mind behind it?

The classic answer is the argument from analogy, given its best known form by John Stuart Mill in 1865. Other people, Mill reasoned, behave as I do, and “they have bodies like me, which I know in my own case, to be the antecedent condition of feelings”, as Avramides quotes him in the Stanford Encyclopedia. So I infer that their bodies, too, come with feelings. The weakness is easy to spot. Critics found it, in Avramides’ words, “problematic that this way of extending one’s knowledge proceeds from a single case.” You would not conclude that every box in a warehouse contains books because the one box you opened did.

Most philosophers today prefer a different route, inference to the best explanation. Scientists believe in electrons they have never seen because electrons explain what they do see. In the same way, other minds are the best explanation for the astonishingly rich, flexible and surprising behaviour of other people. David Chalmers, quoted in the same entry, calls this “as good a solution to the problem of other minds as we are going to get.” Notice the modesty of that sentence. It does not claim certainty. It claims that believing in other minds is far more reasonable than the alternative, which is about as much as anyone can say about electrons, too.

Chalmers also did more than anyone to popularise the thought experiment that makes the problem vivid: the philosophical zombie. The Stanford Encyclopedia entry on zombies, by Robert Kirk, describes zombies as beings “exactly like us in all physical respects but without conscious experiences.” If such creatures are even conceivable, then nothing in a person’s behaviour logically guarantees that anyone is home. Kirk notes that, on some views, “nothing will enable anyone to establish for certain that anyone else actually has qualia.” C.M. Black’s post on Chalmers’ zombies follows the thought experiment into fiction. The question has also become practical again with chatbots, since a fluent conversation partner is no longer proof of a mind. Our post on AI and responsibility takes up that thread.

Brains in Vats and Simulations: Solipsism’s Modern Costumes

The brain in a vat and the simulation hypothesis are often called modern solipsism, but they are really modern versions of Descartes’ demon: they question the outside world, and they usually leave other minds in place.

The vat scenario imagines a scientist who keeps your brain alive in a laboratory and feeds it a perfect virtual reality. The Internet Encyclopedia of Philosophy, in Lance P. Hickey’s entry, calls it a modern version of Descartes’ argument, which “centers on the possibility of an evil demon who systematically deceives us.” Hilary Putnam’s famous reply, in Reason, Truth and History (1981), is that the sentence “we are brains in a vat” undermines itself. If you really were a brain in a vat, your word “brain” would refer to the images in your simulation, not to real brains, so you could not even state the hypothesis correctly. Hickey compares the claim to “all general statements are false”, a sentence that refutes itself the moment it is uttered. Not everyone accepts Putnam’s argument, but it changed the debate: the sceptic now has to explain how his own words get their meaning.

Nick Bostrom’s simulation argument of 2003 is a different animal. In Are You Living in a Computer Simulation? he argues that at least one of three propositions is true: humanity will almost certainly die out before reaching a “posthuman” stage; posthuman civilisations will almost never run simulations of their ancestors; or “we are almost certainly living in a computer simulation.” Bostrom does not claim to know which. He suggests it seems sensible “to apportion one’s credence roughly evenly between” the three. The important thing for our topic is that a simulation, as he describes it, is full of simulated people “with our kind of experiences”. It is a crowded universe, not a lonely one. If you like the idea anyway, our End of Simulation T-shirt wears it discreetly, and the Brain in a Vat Asking AI T-shirt puts the thought experiment and the chatbot question in one picture.

So where is the solipsism? It appears only in the extreme variant where you are the one real person and everyone else is scenery, the plot of a dozen films and the premise of the internet’s favourite insult, which we come to below. The Agent Smith meme borrows the Matrix for social criticism, and our post on Last Thursdayism shows how far this kind of unfalsifiable scenario can be stretched.

Wittgenstein: The Solipsist Is Right, but Cannot Say It

Ludwig Wittgenstein took solipsism more seriously than almost anyone, and his two great books give two different verdicts on it. The early Wittgenstein thought solipsism contained a truth that cannot be stated; the later Wittgenstein thought it rested on a misunderstanding of language.

In the Tractatus Logico-Philosophicus of 1921, Wittgenstein writes at 5.63, “I am my world.” That sounds like solipsism in its purest form, until 5.64 turns it inside out: “solipsism, when its implications are followed out strictly, coincides with pure realism. The self of solipsism shrinks to a point without extension, and there remains the reality co-ordinated with it.” The idea is that the self is not a thing in the world, like a chair or a brain, but the point from which the world is seen, the way the eye is not part of its own field of vision. Once you see that, “only my world exists” and “the world exists” say the same thing. Bertrand Russell, in his introduction to the book, summed up the paradox: what solipsism intends is quite correct, but it cannot be said, only shown. The famous line about the limits of language, the subject of our post on what Wittgenstein meant by the limits of my world, belongs to the same passage.

The later Wittgenstein attacked the problem from the side of language. In the Philosophical Investigations he asks us to imagine a community in which “everyone had a box with something in it: we call it a ‘beetle’.” Nobody can look into anyone else’s box, and everyone says he knows what a beetle is only by looking at his own. His conclusion is that “the thing in the box has no place in the language-game at all”. The word “beetle” works because of how people use it together, not because of the private object. Applied to pain, this is the private language argument: if “pain” meant only “my pain”, as Thornton’s solipsist says, the word could not be learned or used at all. Our language is public, so the moment you think the solipsist’s thought in words, you are already relying on other people. His idea of language games is explained in our post on linguistic confusion, and if Wittgenstein is your philosopher of choice, the Metal Philosophers Wittgenstein T-shirt gives him a heavy metal makeover.

Why Almost Nobody Admits to Being a Solipsist

Solipsism is rarely refuted in a single blow; it is usually abandoned, because believing it turns out to be impossible in practice and self-defeating in speech.

Bertrand Russell put the practical point bluntly in Human Knowledge (1948): “As against solipsism, it is to be said, in the first place, that it is psychologically impossible to believe”, and it “is rejected in fact even by those who mean to accept it.” He then told the most quoted anecdote in the history of the subject: “I once received a letter from an eminent logician, Mrs. Christine Ladd-Franklin, saying that she was a solipsist, and was surprised that there were no others.” The joke tells on itself. If she was right, there was nobody to write to, and nobody else could have shared her view anyway. An article in the Russell journal has since tried to set the record straight on what the two actually wrote to each other, but as a story it has done its job for generations of students.

The deeper point is what philosophers call a performative contradiction. Raymond Tallis, writing in Philosophy Now, notes that “the very act of my asserting it to you makes sense only if what I assert is untrue.” Arguing for solipsism means trying to persuade someone, and persuading someone presupposes that someone is there. Tallis adds the Wittgensteinian point that we think “in a language that’s shared with others, whose meaning is established by a community”, and the observation, borrowed from Gilbert Ryle, that “illusions count as mere illusions only against the background of things that are accepted as real.” You can only suspect that one coin is counterfeit if there are real coins. Following Heidegger’s idea of being-with-others, Tallis ends with a line that would fit on a T-shirt: “There is no ‘I’ without ‘we’.”

None of this proves, with Cartesian certainty, that other minds exist. What it shows is that the solipsist cannot consistently live, speak or even think his position. That is why the Münchhausen trilemma is a useful companion here: every attempt to justify our most basic beliefs runs out somewhere, and at some point reasonable people simply start from the shared world instead of trying to prove it.

Solipsism in Psychology: Children, Astronauts and Cognitive Science

Psychology meets solipsism in three places: in children, who have to learn that other people have different minds; in isolated environments, where the outside world can start to feel unreal; and in cognitive science, which adopted solipsism as a method.

Small children are not solipsists, but they do take a while to understand that other minds can contain different information. The classic test is the false-belief task of Heinz Wimmer and Josef Perner (1983), described in this lecture unit on the origins of mind. A puppet called Maxi puts his chocolate in one cupboard and leaves; while he is away, his mother moves it. Children are asked where Maxi will look when he comes back. Younger children tend to say he will look where the chocolate really is, as if what they know, he knows. Around the age of four, most children start to answer correctly that Maxi will look where he left it. Psychologists call this capacity theory of mind, and in a sense every child solves the problem of other minds in practice long before any philosopher solves it in theory.

At the other end of the scale is what has been called solipsism syndrome. The Wikipedia article on the term describes it as a state in which a person feels detached from external reality and notes that “extended periods of social isolation and confinement may contribute to the development of this condition.” It has been discussed as a possible challenge for astronauts on long missions and in the design of artificial habitats, including a 1970s NASA design study for space settlements. The same article stresses that it “is not currently recognized as a psychiatric disorder by the American Psychiatric Association”. If a feeling that nothing around you is real becomes persistent or distressing, that is worth talking through with a doctor rather than a philosophy blog.

The most respectable solipsism of all lives in cognitive science. In 1980 Jerry Fodor published “Methodological solipsism considered as a research strategy in cognitive psychology” in Behavioral and Brain Sciences. His proposal was that psychology should explain thinking in terms of what happens inside the head, the formal operations of the mind on its own representations, without asking whether those representations are true of the outside world. Fodor did not doubt that the world exists. He was saying that, for the purposes of explaining how a mind works, you can bracket it. Many philosophers objected, and the debate between “internalist” and “externalist” views of meaning, of which Putnam’s brain in a vat is one part, still runs today.

NPCs and Main Characters: Solipsism as an Internet Mood

On the internet, solipsism survives less as a theory than as a mood: the suspicion that you are the main character and everyone else is a background figure running a script.

The clearest example is the NPC meme, after the “non-player characters” in video games who repeat the same scripted lines. According to Wikipedia’s account of its history, the grey NPC Wojak was first posted on 4chan in 2016, and the meme “represents people deemed to not think for themselves”, people said to lack introspection, whose identity is entirely determined by what they consume. It was mostly aimed at political opponents. Philosophically it is a cartoon of the zombie problem, and the article itself lists philosophical zombies under “see also”. The irony is that calling other people NPCs is the least introspective move available: it treats everyone else’s inner life as fake because you cannot see it, which is precisely the step Mill, Chalmers and Wittgenstein all warn against.

“Main character” culture is the friendlier cousin. Dictionary.com traces the trend to TikTok in 2020, when users began filming themselves as if their lives were movies, and “main character syndrome” has since become the label for people who seem to treat everyone else as extras. Romanticising your own life is not solipsism in any technical sense. But the joke lands because it gestures at the same temptation: the world as a stage built around me. If you prefer your existential jokes with a bit more company, our guide to what existentialism is starts from the opposite assumption, that you are thrown into a world full of others.

That, in the end, is the most useful thing solipsism teaches. It cannot be disproved with the certainty of the cogito, and it cannot be lived for five minutes. Every argument for it is addressed to someone, every word used to state it was learned from someone, and every suspicion that the people around you are scenery reveals more about the suspicious person than about the scenery. Plato’s prisoners at least sat in the cave together, which our Plato’s Cave Search and Rescue Team T-shirt remembers; and if you want the full story of that cave and the screens that replaced it, read our post on Plato’s cave and social media.