The Validity of Circular Reasoning (incomplete)

As far as I know, no one has yet solved such questions as “how do you derive ought from is,” or “why is there something rather than nothing”, or “how can we be sure we aren’t just living in the matrix?” The difficulty lies in the fact that the best answers we have to these statements (“you can’t”, “no reason”, “you can’t”) aren’t very satisfying, and more importantly, they cannot be used to derive other conclusions, because of the weakness of the solutions to these initial problems. Is there any way around this? Yes. I’ll address solipsism specifically, the technical term for the “how do I know this isn’t the Matrix” question. Let us assume that I have constructed a beautiful and all-encompassing belief system, showing the path to happiness, virtue, and true understanding of the universe. However, it happens to also say that there’s a 95% chance that we’re actually brains floating in a vat dreaming our whole existence. But it’s a beautiful, elegant, totally logically sound system, it makes a handful of quite reasonable assumptions, and aside from the little disembodied brains problem seems pretty good.

Mostly likely, you wouldn’t accept it. After some discussion, we determine that you would be unwilling to accept any philosophical system that didn’t conclude that the world is mostly as it appears to be.
* So my solution is to simply assume that the world is more or less how it is. Assuming I’m not abysmally bad at reasoning, I should end up the other side with a system that still says the world is more or less how it is. Can I do this? Is it logically valid? Sure!

My formal logic is a little rusty, and even if it wasn’t, I’m not sure how to type stuff in HTML, so let’s do it like this. Let b be “we might be floating brains.” For all world views w, if w implies b, I reject w. For any w I accept, ~b. Hmm… then you do something with introducing other conclusions… universal and existential qualifiers….not sure how it works now. Shit.

I swear I had it worked out. Maybe I’ll post the MacGyver principle of unlikely occurrences first, since that ties in pretty well with this.

* A more likely scenario is that you can’t actually conclude anything without assuming solipsism is invalid.
** I leave “mostly as it appears to be” vague, but I don’t see this as a problem because most people have a reasonable flexibility in terms of accepting that the sun and moon are in fact different sizes, or similar things, and I expect that the theories which assume this would be well within this flexibility.