Okay, so I’ll just make a fairly simplistic objection here. Solipsism as a position is largely supported by arguments from analogy and arguments from possibility; my focus in this quick post will be to question the viability of the latter.
Implicit (perhaps even explicit) in arguing for solipsism on the basis of possibility is that one can cleanly make a transition from epistemic possibility (i.e “as far as I know, X is possible”) to metaphysical possibility (i.e “X is true in some metaphysically possible world”). But there are some problems here, especially where solipsism is concerned. Now, the sort of trick with solipsism is that there is necessarily no observation or empirical evidence which could refute it. From this, it seems to follow that solipsism is compatible with any *perceived* or conceivable state of affairs. But do you see the problem? This makes solipsism unfalsifiable. Not only is there no empirical basis on which to refute solipsism, there is no empirical evidence to *support* it.
So, my admittedly simplistic objection is this: Given solipsism cannot be substantiated, how can one possibly (pun intended) justify solipsism? That is, how can one move from saying “Solipsism is epistemically possible” to saying “Solipsism is metaphysically possible”, when one has embraced a position which lacks any apparent means by which to make the transition from the former to the latter? I’m more or less using a Moorean shift here. Essentially, I’ve got two competing propositions to consider:
“The external world is just an illusion.”
“My mental experience is at least somewhat accurately representing the world as it is.”
The solipsist is attempting to have me put more trust in certain intuitions that the world could be solipsistic than in my continual experience of the world. This move of rejecting one’s pre-theoretical notions of the world itself is not necessarily problematic (cf. Quantum Mechanics and Special Relativity), but for it to be a rational request, there’s going to need to be some pretty persuasive and powerful evidence presented in defense of doing so.And given the lack of support for or against solipsism (because of its inherent unfalsifiability), it seems, on the face of it, that the latter proposition is justified, while the former proposition lacks *any* means of justification. Notice these objections are not just pragmatic in nature, but that they point (so far as I can tell) to a legitimate epistemic problem with the concept of solipsism.