Solipsism is an extreme extrapolation of subjectivism. It arises as a result of an epistemological problem: everything we know is the result of internal thought. It is possible that everything we see, the entirety of what we consider "reality" is an illusion or a trick. Any one of us could be completely insane, suffering from grand delusions, where nothing that is experienced corresponds to reality. Some people involuntarily live long periods of their lives in such a state, hallucinating their lives away1. Metaphysical solipsism is the belief that "your own mental states are the only states": Only your self exists, nothing else2. All is a creation of your imagination, including other beings. Those other beings may appear to be alive but they are actually projections of your own subconscious being - their subconscious is your subconscious, and your limited view of their lives derives from your deeper mind playfully denying your conscious self full knowledge of what is really going on. The whole world plays out in your imagination. Although it is impossible to disprove solipsism, there are some strong arguments against it.
“He who sees everything as nothing but the Self, and the Self in everything he sees, such a seer withdraws from nothing. For the enlightened, all that exists is nothing but the Self, so how could any suffering or delusion continue for those who know this oneness?”
Isha Upanishad, sloka 6
“A man cannot pretend to know what he is in himself from the knowledge he has by internal sensation. For as he does not as it were create himself, and does not come by the conception of himself a priori but empirically, it naturally follows that he can obtain his knowledge even of himself only by the inner sense and, consequently, only through the appearances of his nature and the way in which his consciousness is affected.”
"Fundamental Principles of the Metaphysic of Morals" by Immanuel Kant (1785)3
After much deliberation I seriously entertained the possibility of solipsism, but, abandoned it in 2002. This page presents some arguments that solipsism is not true although this is clearly a very difficult belief to refute as it is impossible to validate any experiences other than your own and therefore impossible to prove the existence of an external world. Nonetheless, solipsism has some problems.
Problems with solipsism:
If the self created all of the universe and all of history as a feat of the imagination, it seems quite odd that we do not have an inherent understanding that this is the case. It is odd that we do not have immense superpowers. If all beings are the result of private reflection, and the universe is a game, created to entertain ourselves, it seems that the rules of physics and the limits of time and space could all be abandoned on a whim. Does anyone have these powers? Apparently not. The solipsist belief system must therefore explain why the ultimate truth of reality is so damn well hidden!
The best explanation is that the godly solipsist self creates the universe as required as part of a game in order to pass time, interest itself, and avoid boredom. But the best way to do this, as an omnipotent being, is to play an active part in the game. This requires severely limiting one's own power. So, the solipsist's subconscious created the universe, but hides this state of affairs from its own consciousness. Therefore, solipsism is arrived at through philosophy, not through instinctive belief or through the self demonstrating creative powers to itself. Only by dividing itself into an ignorant conscious self, ruled by an omnipotent subconscious self, could true boredom-averting procrastination be achieved.
Our subconscious, for want of something to do, created a Universe and created lots of people and created our conscious self also, as the only valid individual in this world. This actually makes solipsism a similar belief system to that of some Buddhists, mystics and pantheists, but merely looking at reality from a different perspective.
The problem is that this is a highly convoluted situation, verging on being simply unbelievable. Although this in itself isn't evidence of its falsity. The final straw for me was this: what is the point of the entire escapade wherein ultimate truth is hidden from the conscious self, when in reality, the solipsist is claiming to actually know that they've created all of reality in their heads? It seems that once a solipsist has realized what the game is, then, the purpose of the illusion has ended. But life goes on as if the solipsist is not the sole reality, after all.
As a solipsist you face a serious problem when you try to explain the belief to someone else. It is nearly impossible to convince anyone that it could be true. There are only two ways to convince someone that solipsism is true:
You have to convince them that they are the valid being, and that you yourself are a projection of their own self. However they'll know you can't possibly believe this yourself and will therefore believe sternly that it is not true.
You have to convince them that they are a projection of your imagination. Which they simply will never believe, because they are conscious themselves.
It appears that it is impossible to state that you yourself are the only valid consciousness in a meaningful way, because anyone who you tell it to will automatically disbelieve you. That is a major problem, it makes solipsism workable only as a completely private belief. It doesn't necessarily mean it isn't true, if you do honestly believe that all the people around you are automatons of your own creation, and do not possess independent consciousness. But it means the belief has no practical consequences, and as it would be ironic indeed to have any pro-solipsism clubs or societies, it seems it also has no social significance as a belief.
Solipsism cannot be tested as a belief; there is no way to confirm or disconfirm it, and it has no practical effect on the world. In science, the inability to test something makes it instantly rejected as a theory. It is as if it wasn't a true belief system. It is a highly abstract solution to a technical epistemological problem that results mostly from philosophical issues that are hard to verify in the real world. Solipsism can be 'safely ignored' without actually being directly refuted. As a belief, it simply doesn't matter. This is the hallmark of something that simply isn't true.
Only one person in the world can be a solipsist and be correct in their belief. If two solipsists ever meet, one of them is deluded. If ten solipsists attend a meeting (I doubt that many more have ever congregated - it is a rare belief!), then nine of them at least must be deluded into thinking that they are the only true conscious being, and only one of them could possibly be the true cause of all existence. Now, if you meet an increasing number of believers and it seems that the vast majority of them must be wrong in their belief, it begins to become a problem for that belief system in general: It might not actually be true for anyone.
Where do the fake experiences come from? They come from the self, generated through imagination. The self makes the conscious self believe these imagined experiences. How did the self come into existence? Why did the self create existence in the way that it did, why does it create experiences? These unanswered questions are no different to the unanswered questions of theism: Where did God come from? Where did the Universe come from? Where did the solipsist self come from? These appear to me to be the same question expressed in different words, but answered internally by no belief system. Its formal name in theological is the first cause dilemma. It seems that any causal explanation that attempts to account for reality itself creates one further question: what was the cause of that cause?
“All causal explanations must have an arbitrary beginning”
This highlights another problem. Solipsism is a belief system that largely exists to answer the epistemological problem of how we verify the world's existence. Solipsism doesn't actually answer this, but merely, like saying 'god did it', creates another question: What created that cause of reality? Solipsism therefore contains the same first-cause problem as other belief systems. This wouldn't matter if only solipsism wasn't based on its ability to answer the hard problem of epistemology. Therefore the belief system as a whole fails.
Consciousness is a product of the Universe, and not the other way round. Biology as the cause of life is also the cause of consciousness. There is simply no reason to presume that simply because you can't validate other life that biology does not create valid consciousness other than your own self. If you yourself logically exist, then there is therefore basis for stating that logic alone can create life aside from your own.
Our 'minds', 'souls', 'spirit' and consciousness are all physical in nature5. Thousands of years of investigation has shown us that our brains comprise and produce our true selves, although because that for most of human history we have had no understanding of how our brains work most Humans have falsely believed inferred that we have souls6 and this idea has infused our folklore, cultures, myths, religions and has instructed our interpretation of dreams7. Souls and spirits do not exist. Our bodies run themselves. We know from cases of brain damage and the effects of psychoactive drugs, that our experiences are caused by physical chemistry acting on our physical neurones in our brains. Our innermost self is our biochemical self.”
You might think that it is a circular argument: If neurology accounts for consciousness, then this could simply be the state of affairs imagined by myself. But it isn't just that: If it is possible at all for biological mechanisms to create consciousness, as it does, then there is simply no need for a roundabout way of explaining that this mechanism is itself the creation of a conscious being. Why bother with the added complications of solipsism? If you abandon solipsism, then, the world (and its many consciousnesses) makes just as much sense from a materialist point of view. For all intents and purposes I became ready to declare solipsism dead, which was a shame because it was real fun while I believed it!
For an interesting discussion on the ability for life to arise given a 'random' universe, see: The Inevitability of Life: The Universe is Fine-Tuned for No-one!.
(2004) Descartes' Baby: How the Science of Child Development Explains what Makes Us Human. Published by Basic Books, New York, USA. In Clarke (2011) p311-312. Bloom is a professor of psychology and cognitive science at Yale University, USA.
Davison & Neale
(1997) Abnormal Psychology. Hardback 7th edition. Published by John Wiley & Sons, Inc. Amazon link points to a newer edition than the one I've used here.
Kaku, Michio. Professor of theoretical physics.
(2014) The Future of the Mind. subtitled "The Scientific Quest To Understand, Enhance and Empower the Mind". Published by Penguin Books Ltd, London, UK. Quotes taken from Amazon e-book.
Kant, Immanuel. (1724-1804) German philosopher.
(1785) Fundamental Principles of the Metaphysic of Morals. Translated by Thomas Kingsmill Abbott (1829-1913). eBook was prepared by Matthew Stapleton. Amazon digital edition.
Russell, Bertrand. (1872-1970)
(1946) History of Western Philosophy. Quotes from 2000 edition published by Routledge, London, UK.