—On the surface level, science doesn’t really answer anything.—
But I would mark that as a great advantage of the process of science: it can have a limited and specific scope. This limited scope means that its hypotheses are falsifiable, and essentially, all parties can know what we are talking about, and the limits to what we are trying to explain. It only tries to answer questions one at a time. This allows us to build our knowledge little by little, instead of trying to take on reality all in one fell (and probably wildly inaccurate) swoop.
—But what about people who are mentally ill? Are their warped (or however you choose to express it) thoughts also real?—
Yes, their thoughts are indeed as “real” as anyone elses. But do not confuse the realness of thoughts themselves with the realness of to what they refer (i.e. truth claims about the state of the world). My thoughts about unicorns are real. But as far as I know, no unicorns actually exist. My belief that unicorns exist can be wrong. That’s the very fundamental of objective exploration: that hypothesises and beliefs can be wrong, thus requiring us to have various measures by which we can correct error. If we were infaliable, unable to think anything other than the truth, then we would never have any need for things like science and logic.
—I mean the simple fact of assuming something to be true. For instance, you assume that you are alive (in the typical sense) this minute, but how do you know? Maybe you are a supernatural entity dreaming about being human. Instead of messing around with such silliness, however, you take it on faith that you are as you seem to be.—
While one certainly could take it on faith, it is not necessary to do so. When we agree on certain basic axioms, we essentially are agreeing not to challenge their truth for the sake of discussion: i.e. we hold them to be true for the sake of the sort of discussion they allow us to have. Almost every single discussion one can have, for instance, requires simply taking for granted the axiom that “things can exist.” This axiom is completely unprovable (any evidence brought forth to prove it would beg the question), but even having a discussion at all about the world around us requires it. I personally don’t take it on faith that we exist: but I’m hard pressed as to what I could possibly talk about if we didn’t. Almost every discussion about truth is premised on the idea, and so I take it for granted for the purposes of exploring what it allows me to explore.
Indeed, a person who believes that we DON’T exist (despite the self-defeating nature of that assertion) can still have a meaningful discussion about existence by simply presuming it for the sake of discussion.
One major line of evidence in science is induction. Induction is never 100% proof, and it would be wrong to think that just because I have not passed right through my chair as I sit down it, that it could never happen. However, I do have strong inferential experience from myself and others that this doesn’t happen. I shouldn’t, however, start taking it on faith that it could never happen. Instead, I can just say only as much as I really know: that we’ve never encountered an instance in which it has happened, and IF reality has any consistent regularity (an assumption!), then it is not likely that it will happen either. That way I avoidthe complete ingorance as to the normal behavior of chairs that I would otherwise be stuck with, but without turning it into a matter of faith.
—Of course, you do trust your senses. Everyone does. But the question is one of whether or not you are justified in trusting those senses, or if you are experiencing an illusion.—
But this, ultimately, is not a question that can really be answered. If our senses are not at all reliable, then we’re sort of stuck, and we can discuss very little about the world around us. We presume that our senses give at least a moderately accurate picture of the world in order to discuss what everyone seems to sense being a common part of. If what we are discussing is just a collective illusion, so be it, but it hardly makes any difference to the discussions we have when we sit down to discuss things based upon the premise that our senses are somewhat reliable as means of gathering evidence.