(I had Jimmy Stephens rewrite this and I think his additions made it better.)

Oftentimes, Christians face questions about skeptical scenarios. These scenarios come in different degrees or strengths or tiers of skepticism. For example, there is skepticism about the external world. There’s skepticism about the reliability of our empirical senses. There’s skepticism about other minds. There’s skepticism about religious language or skepticism about science. There’s skepticism about Christ’s resurrection. There are all different tiers of skeptical scenarios.

The strongest tier of skeptical scenario undermines knowledge. It is skepticism about the possibility of knowledge.

In my experience, there is a debate over the necessary conditions of knowledge. Just what is needed to know something, anything? In response to skeptical scenarios about the possibility of knowledge, some thinkers say you need to rule these out in order to know anything. For them, these scenarios constitute defeaters for entire epistemological systems. Others say you can have knowledge without ruling out these scenarios. They say you can have knowledge without knowing that knowledge is possible.

I have two comments on this topic. First, let’s consider solipsism.

Solipsism is sometimes expressed as the view that “I am the only mind which exists,” or “My mental states are the only mental states.” However, the sole survivor of a nuclear holocaust might truly come to believe in either of these propositions without thereby being a solipsist. Solipsism is therefore more properly regarded as the doctrine that, in principle, “existence” means for me my existence and that of my mental states. Existence is everything that I experience—physical objects, other people, events and processes—anything that would commonly be regarded as a constituent of the space and time in which I coexist with others and is necessarily construed by me as part of the content of my consciousness. For the solipsist, it is not merely the case that he believes that his thoughts, experiences, and emotions are, as a matter of contingent fact, the only thoughts, experiences, and emotions. Rather, the solipsist can attach no meaning to the supposition that there could be thoughts, experiences, and emotions other than his own. In short, the true solipsist understands the word “pain,” for example, to mean “my pain.” He cannot accordingly conceive how this word is to be applied in any sense other than this exclusively egocentric one.

https://iep.utm.edu/solipsis/

My objection to these schemes is that man’s mind is not a se. Man is not self-existent; the human mind is not self-sufficient. The usual motivation for solipsistic notions is that we can’t get outside our own experience to verify that our experiences are veridical. This is sometimes called the egocentric problem of knowledge. One cannot escape the prison of his subject-hood and so cannot, as C.S. Lewis put it, pull his eyes out to then look back in on themselves. But if we should be skeptical about the trustworthiness of our own experiences, then we should doubt for the same reason that a human mind can be trusted to explain all the diversified unity, beauty, and knowability of his own experience in the first place. If humans aren’t trustworthy to get beyond their subjectivity, then humans aren’t trustworthy for knowledge of their subjectivity in the first place. The selfsame skepticism that was supposed to motivate solipsisism undermines itself.

Furthermore, I suppose that a Christian lacks sympathy for solipsistic skeptical scenarios. This lack of sympathy arises because Christians have Someone outside our experience that has designed human experience and reality exhaustively. So solipsism never becomes possible on a Christian worldview.

http://spirited-tech.com/2019/09/01/the-unity-of-knowledge/

http://spirited-tech.com/2019/09/02/hive-mind/

Another series of objections to solipsisism come from the family of objections against unitarianism. Suppose solipisism is true. The universe consists in nothing but your own first-person experience. In this scenario, either you would be a loving being or you would not. If you’re not, then why suppose that you’re the kind of person who can be trusted to tell the truth? An unloving person might lie even to themselves, much less the imaginary minds in their inner world. You would be, to yourself, indistinguishable from an unhinged autotheist bent by delusions of grandeur. But worse, if you claim to be a loving person, that claim is incompatible with solipsism for the same reason that it’s incompatible with unitarianism.

Observe:

http://spirited-tech.com/2020/05/06/unitarianism-and-gods-loving-kindness/

If solipsism is true, and all the universe is reducible to your mind, then you have to wonder why you’re not omniscient. If everything that exists is present to your first-person experience, how could anything fall outside of your conscious awareness? You would not only have to be infallible – you would have to be all-wise, possessing an exhaustive conception of everything in existence. Most solipsists are sane enough to admit they are fallible, let alone not omniscient.

There are also issues with regard to logic and your mind. Hays once said:

But that means logic is just a product of my contingent mental states. In that event, we can rule out the possibility of solipsism because it nullifies logical necessity. On that view, you can’t even affirm or deny solipsism because the law of identity requires logical necessity.

http://triablogue.blogspot.com/2018/07/sye-clones.html

Perhaps the greatest argument against the skeptical scenarios of solipsism comes from Hays’ use of McTaggart:

Another point must be considered in reference to omnipotent personality. Human personality is never found to exist without the recognition of the existence of something not itself. (We may follow Hegel’s example in calling this the Other of the person. Other is a better term than Non-ego, since that may suggest that what is recognized by one person as not himself must not be any other person, but something impersonal, and this suggestion would be wrong, for what I recognize as not myself may quite well be another person.)

We only realize our personality insofar as our consciousness has a content — a manifold to which the centre is formed by that I, awareness of which constitutes personality. And this content of consciousness involves for us the recognition of an Other. This may be direct, as when I know something other than myself, or have some volition regarding it, or some emotion towards it. But even when the Other is not involved directly, it is involved indirectly. It may be that that which directly occupies my consciousness is some part of my own nature, as when I think of past events in my life, or will to correct a fault in my disposition. But when we inquire into the nature of those events, or of that fault, we find that they include, or in the long run involve, the recognition of the existence of an Other.

Nor is this recognition, for finite personality, a limitation or imperfection, which it is impossible to remove altogether, but which hampers the fullness of self-consciousness. On the contrary, the more vivid, definite, and extensive is our recognition of the Other, the more vivid and definite becomes our self-consciousness. As consciousness of an Other becomes vague and indefinite, consciousness of self becomes vague and indefinite too.

Hays’ helpful explanation:

I take McTaggart’s argument to be that a solitary being can’t only be aware of himself because self-awareness is a relation requiring background awareness of whatever else is not oneself, which is lacking under that scenario. An argument ad impossible for a solitary self-conscious being.

So, for instance, while newborn babies have minds, they lack the cognitive development to be self-aware in distinction to their immediate surroundings. The introspective knowledge of my existence as a distinct being. Where that ends and something else begins.

https://triablogue.blogspot.com/2017/11/is-unitarian-theism-impossible.html

The Hays-McTaggart critique would imply that a unitarian being is impossible. For the same reason, solipsism is impossible. For on both views, metaphysics is reducible to a unipersonal mind, and so runs into the problem of the “Other” spelled out above.

We can conclude that Christians have some unique tools to deal with skeptical scenarios.