I found this critique of solipsism insightful and worth sharing. Below is the video's transcript.
A common question I hear from people is concerning solipsism. I've gotten many emails on questions of how to address solipsism and how, under idealism, we can justify the existence of other minds. In this video, I hope to provide a critique of solipsism.
The first thing is to consider what solipsism says. If solipsism is true, then only your mind exists; the world that you experience every day is simply a figment of your imagination. In fact, if solipsism is true, then this video is a figment of your imagination. However, there are, in fact, many reasons why we should reject solipsism. While one cannot completely refute solipsism, one must always remember that just because solipsism is always a possibility, that doesn't make it a probability.
The first problem with solipsism is that we cannot control the external world with our mind. If the world only exists in our mind, then we should be able to control it, yet this is not the case. One response to this objection might be that the external world is simply the uncontrolled part of the mind that the conscious agent is exploring. So, the external world is much like an uncontrollable dream, or the entire external world is within your mind, but you, as a character in the dream, is simply exploring your own mind to learn more about it.
However, this response, while logically consistent, has to make unnecessary assumptions about how nature operates on its own. If we are to accept that we cannot control the external world, and if under solipsism everything is mental, then it must be some more powerful aspect of the mind that the solipsist cannot control. And this would collapse into theistic idealism, in which the godlike aspects of the mind the solipsist cannot control is in control of the actual asserted external reality of the solopsist.
The second problem with solipsism is that it fails to explain basic facts about reality in a way that is not ad hoc. There are three facts that we need to explain: one, that there are tight correlations between a person's reported private experiences and the observed brain activity of the person; two, that we all live in the same shared world; and three, that reality works independent of our personal volition.
Once again, one would have to say that something outside the conscious agent is the uncontrolled reality of the conscious agent. While these facts could technically be explained by solipsism, it would be no more different than saying that these facts were divinely implanted into the universe to only give us the illusion that the person's brain is correlated with mental activity or that we live in a shared world. And so, once again, this becomes an ad hoc explanation.
The third problem with solipsism is that it is anti-intuitive. We should remember that an important concept called epistemic particularism, which is a formal response to skepticism. It implies that if we have good reasons to think that our beliefs are true and no good reason to doubt them, then we should not doubt them. We have good reasons to think other minds exist through our interaction with other human beings, and it's intuitive to think that other people or other human beings have minds of their own. Therefore, since there is no good reason to think that other people don't have minds of their own, then it is epistemically more probable that there are other minds, and therefore, solipsism is false. Again, while this does not disprove solipsism, it shows solipsism to lack explanatory power.
The final argument shows the incoherence of solipsism when it comes to how the mind actually learns language. While solipsism is logically consistent, it actually has trouble explaining the fact that language is largely created in a public fashion. Even when someone does create some kind of what’s called a “private language,” that language was still formed by some previous language. In fact, many of the languages that exist today are really just modified forms of older languages that change over time. So, even if language could be private, that doesn't mean a creation of language isn't borrowed from a previous language that the person used.
This means that if language exists, then it would need to borrow from a public language center. In other words, if someone were to create some private language for themselves, any claims that they create would depend on the much larger public language. Language is an irreducibly public form of life that is accounted for by specific social confluence. Each natural language system contains what’s called “language games,” governed by rules. To question, to argue, or to doubt is to utilize language in a particular way; it is to play a particular public language game.
The proposition that "I am the only mind that exists" makes sense only to the extent that it is expressed in public language, and the existence of such language itself implies the existence of a social context and, therefore, other minds would be involved. Therefore, solipsism presupposes the very thing that it seeks to deny, which is a public forum in order to even have the language to ask questions and say things like "I am the only mind that exists." The only way out of this objection is if the solopsist’s mind was omniscient. However, this is not the case since a solipsist doesn’t know everything about the contents of its own mind; he is simply exploring the uncontrolled, more powerful aspects of his mind.
In fact, in order for the solipsist to have language, the more powerful aspect of his mind would have to be omniscient in order to somehow have the knowledge to create the language for him. And this would once again imply some godlike entity that is truly in control of these solipsistic experiences. Therefore, with all these objections put forth, it is clear that solipsism is an inadequate explanation of reality. With the objections piled up, we see that solipsism is not a good theory in explaining the data. While none of these objections are successful in completely refuting solipsism, they all simply show solipsism to be ad hoc and not parsimonious. So, ultimately, solipsism is unsustainable on its own, and therefore, we have very good reasons to think that there are other minds that exist other than ourselves.
It isn't always necessary to have a defeater for a worldview. Sometimes you just need to show the untenable positions it leads to and that's enough of an argument. Most atheists/agnostics do not take solipsism seriously even though there's no clear defeater for it. They say "it's radical" although that isn't necessarily an argument but just a way of stating "it's uncomfortable ". The same thing can also done for atheism/agnosticism. You don't necessarily need to have a defeater for it. Just show that there are two hills to die on, one that inevitably leads to radical skepticism, and another with an epistemology that is more in line with how human beings normally operate.