The Instigator
Pro (for)
2 Points
The Contender
Con (against)
16 Points

Metaphysical Solipsism is Most Likely True

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Voting Style: Open Point System: 7 Point
Started: 1/10/2015 Category: Philosophy
Updated: 1 year ago Status: Post Voting Period
Viewed: 1,961 times Debate No: 66673
Debate Rounds (4)
Comments (17)
Votes (5)




Let's do it n7.

Pre-Debate Notes:

Note that all arguments made from my side are intended to be read from first-person perspective. As they relate to *Your* mind, indeed it is *You* the voter that I intend to demonstrate solipsism is true for.Thus when I mention 'I' or 'my' etc., it is for the purposes of ease of reading, rather than an acknowledgement of *my* (As in 'Envisage', the debater) mind's existence.

Metaohysical Solipsism: "Metaphysical solipsism is the "strongest" variety of solipsism. Based on a philosophy of subjective idealism, metaphysical solipsists maintain that the self is the only existing reality and that all other reality, including the external world and other persons, are representations of that self, and have no independent existence"

Round 1: Acceptance, Definitions
Round 2: Opening arguments & rebuttals
Round 3: Arguments & Rebuttals
Round 4: Rebuttals & Conclusion (No new arguments)

Message me if you wish for any changes in the format, definitions etc.
Debate Round No. 1


I thank my distinguished mentally constructed opponent n7 for accepting this debate! Alas let me begin.


I will be taking two approaches to this resolution within this debate. The first is to directly affirm solipsism via. epistemological grounds. I.e. We should prefer belief in solipsism to be true outright. Secondly I will argue for solipsism via. idealism. Thus I will establish that physical reality doesn’t exist, and thus only mind exists. Then, via further arguments I will establish that solipsism is the only compatible philosophy assuming idealism.

A1. Epistemologically Preferred Position

We cannot doubt our own mind. Cogito ergo sum (I think therefore I am) establishes that any act of doubting one’s own mind automatically presupposes there is a doubter (you), thus we can have certainty of our own minds existence.

The same however cannot be said for ‘external reality’, external reality is but a conjunct of experiences in the form of various qualia (sensations of colour, sounds, touch, etc.), however there is nothing inherent that ties them to the fact that external reality exists. We can be certain that the qualia exists within our minds, but we cannot justifiably make any claims that these qualia represent anything external to our minds. Thus we should reject this notion purely on Occam’s Razor grounds. Solipsism simply makes fewer assumptions than any other ontology.

A2. Argument From Idealism
Mind does not reduce to non-mind
I will establish idealism is true in two parts. First by establishing that non-mind is not fundamental, and second by establishing a multiplicity of substances is a false ontology, which leaves the conclusion that monistic idealism entails.

Leibniz Law of Identity of Indecernables
This law dictates that for two things to be the same that they must have the same properties. For whatever is true for one must be true for the other. What is metaphysically possible for one must also be metaphysically possible for the other, and so on and so forth. If everything is true for one is also true for another, and vice versa, then both things are the same.

P1) If mind is non-mind, then what is true for mind is true for non-mind
P2) It is true that it is possible for mind to exist in a solipsistic world
P3) It is not true that it’s possible for non-mind to exist in a solipsistic world
C) Thus, mind is not non-mind

Defence of P1
This is true by Leibniz Law of Identity of Indecernables.

Defence of Premise 2
Solipsism is a logically self-contained universe, for it to not be metaphysically possible then it must entail a logical or metaphysical incoherence, yet solipsism remains a stubburn (albeit annoying) philosophy to this day. For virtually any inductive argument given in favour of another ontology such as physicalism is also compatible with solipsism, since the world exists as a perception. Virtually anything said of the physical can be reduced coherently to the mental.

Defence of Premise 3

Premise 3 is true by definition, only a world of idealism is compatible with solipsism, thus it is impossible for a non-mental substance to exist in it.

Should follow deductively if the premises are true. The only premise that can be realistically contested is premise 2, which can only be false if it is metaphysically impossible. A tough burden for Con to overcome!!

Substance Pluralism is false
So far the immaterial nature of mind is established, thus now to address pluralism, the notion there is more than one substance.

Interaction Problem
The most trivial reason to reject poluralism is because, assuming pluralism is true, then the mental must interact with the non-mental. I.e. your mind tells your arm to move, and your arm moves. If pluralism is true, then your mind (which doesn’t reduce to non-mind, or material, etc.) must somehow interact with non-mind. But how is this even possible if they are fundamentally different substances.

It would be akin to a ghost with no physical properties pushing a block across the table, it needs to interact somehow!

Another problem is inductive. IF it was true that the mental interacts with the non-mental, then we would expect evidence of this ‘interaction barrier’, or this ‘third substance’ with the shared properties, such as a substance with both qualia and electric charge which we can detect with both ‘physical’ methods, or ‘mental’methods. Yet evidence for this is absent.

Furthermore, our laws of physics are essentially closed, thus if there existed both non-mind (which is detectable physically) and mind (which is not in pluralism) then we would expect our laws of physics to be causally open. We would not expect the law of thermodynamics to hold, nor any other uniformity laws (such as energy conservation), since there would be the ‘void’ where the open non-mental world would be spilling interaction, energy, etc over to. This is obviously, false.

Thus, monistic idealism entails.

Metaphysical Solipsism is Necessary
This argument is adapted from knownnomore’s refutation of idealism, ironically this refuation only world if solipsism is false, I intend to adapt it to show solipsism is necessary.

P1) Mind is fundamental
P1) If mind is fundamental, then either my mind is fundamental, or another mind is fundemental
P2) Another mind cannot be fundamental
C) My mind is fundamental

P1 I have already justified so far. P2 follows de facto, mind is fundamental, thus some mind must be fundamental, either mine or someone elses. Something must ground reality in some form.

Thus I only really need to justify P2. This rather trivial. IF another mind is fundamental, while all other minds are contingent, then there needs to be a reason for why one mind si fundamental, but my mind is not. This reason cannot be encapsulated within “it’s mind”, because that would entail another substance, thus we cannot have a reason for this difference that is within the ontology of idealism, thus the reason cannot exist and the notion of another mind being fundamental is also incoherent. Otherwise there would be something external to idealism that is fundamental, which I have already proven so far is false. Thus solipsism entails.

Back to Con!


Thanks to my real, existing, sentient opponent Envisage. I would like to remind everyone there is no matrix and to obey their government.

Epistemologically Preferred Position

Here Pro is arguing because we cannot know there is an external world outside our perception that via Occam’s Razor we should reject such a thing. We may prima facie be able to see only our private mental events, but does this really make less assumptions than thinking there exists an external reality? It seems it doesn’t. It seems reasonable to think we are beings inside a world instead of the authors of it. When our apparent eyes are damaged, so is our qualia. When our ears are damaged, so too is the qualia and so on. Solipsism would hold this is an illusion, but now we see solipsism is making the bigger assumptions here. Solipsism would hold fundamentally what happens to the eyes has nothing to do with sight which flies in the face of our reasonable assumption.

So too does solipsism have no reason for the apparent existence of the brain. There isn’t anything about the brain that has any relevance to the mind, even though it appears to be some type of CPU of the mind. Solipsism has to assume our everyday views of cause and effect in respect to our bodies are all wrong along with the radical change of how we think about our brains.

Argument From Idealism

Pro presents an argument for idealism then an argument for solipsism based on idealism. I will focus on attacking his argument for idealism. His defense of it stems from the modal argument. Basically he says if mind=physical then solipsism should be impossible, but solipsism is possible therefore mind isn’t fundamentally physical (or non mind).

A huge problem is that this argument only works within the realm of Kripkeian modal metaphysics. There are alternatives that seem much better, such as David Lewis' counterpart theory. This theory denies transworld identity. Which is the idea that when we're speaking about possibilities we're speaking about the object's identity preserved into the realm of possibility. In other words, its identity is the same throughout possible worlds [1]. However, Lewis' theory “identifies possibly being F with having a counterpart—an appropriately similar object in another possible world” [2].

This model hurts the modal argument because it means a counterpart of the mind can exist alone, not because it's not fundamentally non-mind, but because there exists different counterparts in different contexts. As Dr. Derek Ball puts it

“ ...she succeeds in generating a context in which “possibly, pain =/= c-fiber firing” is true. But this does not entail that pain =/= c-fiber firing; it only entails that pain/c-fiber firing has different counterparts according to different counterpart relations. The worlds that make an utterance of “possibly, pain =/= c-fiber firing” true are not worlds in which pain=/= c-fiber firing, since there are no such worlds; instead they are worlds according to which pain =/= c-fiber firing. So the physicalist can rest easy; the argument is invalid.” [3]

We have good reason to accept this theory, one being from the problem of accidental intrinsics. I have dark hair and it is possible that I have blonde hair. If transworld identity is sound then in a possible world I am the same object, but I have blonde hair. However, since black hair is a part of me, then in order for me to be the same object I would have to also have black hair. This is a contradiction, as I cannot have both black hair and blonde hair. We have to say in this possible world, there exists my counterpart with blonde hair.

Furthermore, this argument would only show the mind doesn’t reduce to non-mind. There are plenty of theories that aren’t substance dualism but still accept the irreducibility of the mind [4][5]

We have good reason for adopting a counterpart theory of modal metaphysics which allows me to resist the argument for idealism. Furthermore, the argument from idealism doesn’t take into account other theories of the mind.

I will now turn my attention to two arguments against the resolution

Testing solipsism

It seems to me that we can actually test solipsism. How? Well, if my mind creates reality then I should be able to control reality? There would exist nothing but my mind, yet there must be a restriction in place that prevents me from being omnipotent. This restriction obviously isn't conscious, nor would it seem to be mental at all. Any meaningful restriction wouldn’t seem to be mental as it must be something that governs the mental.

Solipsism is incoherent

Here I will be arguing that to think the thoughts “Solipsism is true” or to even read this debate you must assume solipsism is false.

Without language, you wouldn’t be able to read this and wouldn’t be able think thoughts about solipsism like the ones above. If solipsism is true, then language would come about in a purely private manner. However, as Ludwig Wittgenstein pointed out, a private language is impossible [6].

Someone who has no language stranded on an island makes a mark “s” whenever he has a certain sensation. This however has no criteria of correctness. It has no rules governing when it’s used correctly, it can be used however one wants in an arbitrary way. Language then is used in a social context. A group of people come up with rules and correct the said behavior so others may learn the language.

So in order for Pro to write an argument for solipsism, believe the statements in solipsism, and understand this debate, he must first assume solipsism is false.

Now to Pro

[1] Chisholm, Roderick. "Identity Through Possible Worlds: Some Questions,"

[2] Sider, Ted. 2006. “Beyond the Humphrey Objection”

[3] Ball, Derek. 2011. “Property Identities and Modal Arguments.”



[6] Wittgenstein, Ludwig. 1974. Philosophical Investigations.

Debate Round No. 2


Envisage forfeited this round.


What did the solipsist say when he broke up with his girlfriend?
It's not you, it's me.
Debate Round No. 3


I am going to have to drop this debate, had a few things happen over the past week which has diverted my time and attention. Voters, please vote for n7, and I am really sorry for wasting his time, and appreciate the commitment he has made to this debate already.

Thank you & I am sorry again to n7, mentally constructed or not.


Pro conceded, he had real, existing, non mental things to attend to.

Thanks anyway.
Debate Round No. 4
17 comments have been posted on this debate. Showing 1 through 10 records.
Posted by Envisage 1 year ago
Posted by Envisage 1 year ago
I am not quite sure about it. But telling you the problems I have with it will be helping you refute my case so I won't go into detail =p. I like him, he's very lucid, I usually disagree on several points with atheists on philosophy but I don't usually find much I disagree with him on much once I wrap my mind around what he says.

Not sure if that's a good thing or not...
Posted by n7 1 year ago
I've forgotten about knownnomore. What do you make of his argument against idealism? I just watched that video, it seems really interesting, but I am not sure about the "Ego Tunnel" rebuttal.
Posted by n7 1 year ago
You could have posted the sources in the comments. In any event, the sources aren't extremely critical because the main content is there and this debate will mostly (if not all) be deductive anyway.
Posted by Envisage 1 year ago
I am sorry about the half-baked arguments. I got locked outside my office for 30 mins and didn't have time to source it etc. The main content is there though.
Posted by Envisage 1 year ago
*cracks knuckles*

Warning... the arguments that follow may contain significant levels of b*llshit, approach with caution.
Posted by Keeyan 1 year ago
Why would you want to debate a projection of your own consciousness? Or why would I want to debate a projection of my own unconsciousness? Or maybe everyone in the comments section are simply projections of whomever reads this comment.
Posted by nSlo 1 year ago
I'd like to accept your debate since it's about a wonderful topic, and it would be the first one for me on this website as well...please do message me if you accept my request.
Posted by UndeniableReality 1 year ago
Is the question of solipsism answerable and does its answer have any impact in reality?
Posted by Wocambs 1 year ago
I think I could put forward some interesting arguments against this.
5 votes have been placed for this debate. Showing 1 through 5 records.
Vote Placed by Zarroette 1 year ago
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Reasons for voting decision: Pro gracefully concedes.
Vote Placed by Paleophyte 1 year ago
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Reasons for voting decision: Pro forfeited
Vote Placed by Ragnar 1 year ago
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Reasons for voting decision: Concession. Hopefully you can have a rematch.
Vote Placed by NoMagic 1 year ago
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Reasons for voting decision: Either Envisage made some internal excuse up to get out of this debate or he had an external excuse that means he is wrong concerning this debate. If I think, I am, this is what Pro argued. I'm pretty sure I'm not Pro. So Pro must be wrong. Con gets the win.
Vote Placed by Lexus 1 year ago
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Reasons for voting decision: I'm giving pro conduct because he gracefully backed out of the debate, but all other points go to con