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THBT: Metaphysical Solipsism is Likely Correct


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THBT: Metaphysical Solipsism is Likely Correct

Bones: Metaphysical Solipsism is Likely Correct
Contender: Metaphysical Solipsism is Likely Incorrect

Metaphysical Solipsism: The philosophy of subjective idealism that asserts that nothing exists externally to the mind and that the external, physical world and other people are representatives of the mind and have no independent existence.

1. No Kritik.
2. No new arguments are to be made in the final round.
3. The Burden of Proof is shared.
4. Definitions are agreed upon and are not to be contested.
5. Rules are agreed upon and are not to be contested.
6. Sources can be hyperlinked or provided in the comment section.
7. A breach of the rules should result in a conduct point deduction for the offender.

Round 1
Thx Sum1hugme for accepting this debate. 

Contention IEpistemological Parsimony

The Munchhausen trilemma is a thought experiment used to demonstrate the theoretical impossibility of justifying any truth without unjustifiably accepting certain axioms. The trilemma posits that there are only three ways of completing a proof: 

  1. Circular argument 
  2. Regressive argument
  3. Axiomatic argument
The first involves using the conclusion of an argument as a premise. An example of this is: “1+1=2 because 1+1=2”. Clearly, this is unsatisfying as the contrapositive would dictate that this method of reasoning can support any imaginable proposition. The second, regressive arguments, is also unsatisfying, as it results in an infinite regress, where each proof would require further proof, ad infinitum. The third option is most commonly used, yet it assumes the veracity of certain axioms. Instead of defending the precepts, an axiomatic argument merely asserts them to be true. Though Hume's guillotine was initially presented as an argument against moral truths, it can be used here to demonstrate why the axiomatic argument is not satisfying. Seemingly factual statements such as water consists of two parts hydrogen and one part oxygen are established under the assumption that people ought to value things such as evidence, rationality and reason, thus they cannot be objective truth claims.

This invites the search for an indisputable fact which presupposes all knowledge. As Descartes famously declared, cogito ergo sum. The only certain and irrefutable fact is that one’s mind exists, as it is impossible to doubt the mind’s existence, because doing so would entitle that there is a host for the doubter i.e. yourself. This level of certainty, however, does not extend to the external reality. Humans perceive (or so we think) reality through some form of qualia, however there is no reason to believe that they are indicators of an external reality. Whilst we can be certain that our qualia exists within our mind, there is no reason to believe that they provide any insightful tellings of the “real world”. 

Thus, the existence of the physical world can be discarded purely on the basis of Occam's razor, which asserts that a theory is more likely if it has lesser ontological commitments than a competing theory. As metaphysical solipsism posits fewers ontological assumptions than any competing theory, it ought to be deemed as that which is most likely to be true. 


Contention II: Monistic Idealism

Monistic Idealism is the position that all of reality consists of a single substance, being the mind. Such idealists hold that nothing outside the mind is true, and that the external reality does not exist. The position is defended by the following.

p1. The mind and the non mind are distinct entities. 
p2. The mind cannot interact with the non-mind 
p3. If p2, it is likely that the non-mind does not exist. 
c1. Therefore, it is likely that metaphysical solipsism is true. 
The first premise is contingent upon Identity of Indiscernibles, which dictates that no two things have exactly the same properties. As the mind and non-mind are distinct entities, they must also be distinct in terms of their properties. 
The cogency of the second premise is affirmed on the grounds of what is known as the Princess Elisabeth attack on Decartes' dualistic theory. The attack dictates that given the mind and non-mind are polar opposites in terms of composition, it is impossible for the two to interact with each other. In particular, Elizabeth employs the following principle:
  • When A causes B, there must be some connection by means of which this causal relation occurs.
To assert that the mind and non-mind can communicate would be like declaring that an invisible, intangible, inaudible and undetectable fairy can make changes to the physical world. Clearly, there requires a third substance of which ties the physical and non-physical together, however, there is an absence of evidence for such a substance. 
Premise 3 is valid as it has already been demonstrated that the existence of the mind is certain, whilst the non-mind is not. As premise two dictates that the non-mind and mind cannot communicate in any known way and it is known for certain that the mind exists for certain, the non-mind therefore does not exist. Moreover, if the non-mind were to exist, it would not be perceivable by the mind, as this would be analogous to fairies interacting with the physical world. 
Thus the conclusion is valid if premise 3 is true. As it has been shown that it is indubitable that the mind exists, whilst it is uncertain that the non-mind exists, the likelihood of metaphysical solipsism logically follows. 


Whilst the notion that our qualias can be trusted in constructing an objective reality is often thought of as a plain fact, Descartes dive into skepticism finds that this concept is supported by faulty reasoning. To support this notion, I postulated that metaphysical solipsism is the most preferable ontology in regards to epistemology – this is true due to Occam’s Razor – solipsism is simply the least ontologically committed ontology. Secondly, I imposed the argument from monistic idealism which stipulates that reality consists only of a single substance, being the mind. I professed that it would be logically incoherent for the two to interact with each other and would logically require a third substance to act as a medium for interaction; yet evidence of such doesn’t exist. As such, the likelihood of metaphysical solipsism is entailed from both arguments.

  Thank you Bones for this debate. This has been a crazy week for me, so I apologize, but this will not be a long opening.

  Solipsism is untenable. Firstly, Descartes was not arguing for solipsism. He was trying to deduce down a single irrefutable logical fact, that we can build from. Solipsism defeats this endeavor by making it impossible to build up from there. 

  The concept of "I" that is central to the solipsist argument is incoherent under solipsism. In order for the concept of "I" to be coherent, there must necessarily be a "Not-I" to be able to separate the concepts. I can know that the not-mind exists with the same certainty that the mind exists, because they're logically necessitated by the language. Additionally, the act of having a thought necessarily entails time within which that thought can take place, and space within which the mind may exist. Therefore, the existence of the external world is equally as likely as the existence of my mind within it.

  Furthermore, solipsism cannot account for the problem of other minds. It would require a great deal of evidence denial, possibly a denial of all non-purely-rational epistemology in order to preserve a belief in solipsism. There are a plethora of minds that appear independent of my own. They know things I don't know. They have plans I'm not aware of, and they can beat me in mental competitions. If their minds are my mind, the fact that I cannot know the thoughts of these apparent other minds stands out as an argument against that statement.

  Finally, solipsism rejects the existence of the physical world, therefore it must reject the wealth of scientific knowledge that has been a acquired and applied by other minds, and the power of these explanations to predict phenomena that I and my opponent cannot predict.

  In conclusion, all evidence indicates that solipsism is likely false. In order to preserve solipsism, my opponent must reject science. He must rationalize why other minds appear to exist and have knowledge I or He doesn't have. And finally, my opponent cannot articulate "I think, therefore I am," without conceding certainty of the non-mind by logical necessity
Round 2
Thx Sum1HugMe. 



Due to my opponents IRL commitments, they have not responded to either of my 2 arguments. Hence, I extend them.  



CON alludes to multiple arguments to affirm his position. To steel man them, they are as follows. 

  • 1. The concept of I suggest that there is a not-I
  • 2. The problem of other minds
  • 3. Solipsism rejects the physical world and therefore it rejects science. 

This is a purely semantic point. CON admits this and asserts that "[not-I is] logically necessitated by language", however my argument dictates that everything is a product of the mind, including language. Furthermore, the fundamentals of this argument is also flawed. Consider the following syllogistic rendition of CON's argument. 

p1. The concept of I exists. 
p2. The concept I necessitates not I. 
c1. Not I exists. 

Which if valid, can be used in the following 

p1. The concept of not God exists
p2. The concept of not God necessitates God. 
C1. God exists. 


This point can be refuted by the existence of the subconscious state, which is a part of the mind which is not focally aware, yet influences one’s actions and feelings. It can be argued that all of the imaginative capacity that one doesn’t “recollect” doing are done subconsciously. Take dreaming as an example. I cannot “recall” creating or imagining the dreams, but it is my mind that does all of the “creative work” for them. Why is it that when I am dreaming I have the capacity to recreate a full reality, but somehow my mind would be incapable of imagining all of reality as a whole?


My opponent asserts "solipsism rejects the existence of the physical world, therefore it must reject the wealth of scientific knowledge that has been a acquired and applied by other minds". This claim can be refuted with an analogy. Imagine yourself to be playing GTA V. Within the game, you can survive situations which are impossible in the real world. There are scenarios in the game which are only possible in the game, and never in real life. The game file can be analogous to the physical world. Though both follow strict rules, these rules only apply in particular circumstances - the rules of GTA only apply to the game and the laws of science only apply to the physical world. However, notice how these rules can never be used as evidence for objective the existence of this subject. One cannot say "denying the world of GTA would mean you must deny the strict, unchanging rule within the game, this is absurd!", as the rules only dictate things within the game, and not outside of it. Though science can make observations of the "material world", it cannot prove that this entire world isn't inside the mind. 

Back to you. 
I'm not going to be able to post an argument in time, so consider this a formal concession. Sorry Bones.
Round 3
Thx sum1hugme. Completely understandable, perhaps we can run this back some time. 
Yeah absolutely. FIN