The medieval Christians and Muslims tried to systematize the world metaphysically through foundationalist epistemology, and insofar as you can assume properly basic beliefs hold, you can actually take that pretty far. Until you get a David Hume, who attacks the foundations of proof, what it even constitutes, how you can even go about justifying your most basic assumptions, and then the entire method eats itself. Modern philosophy like Nietzsche is more like psychology than it is classical philosophy.
Discussion
#[0] Yeah the impression I got was that old philosophy was sort of a precursor to science.
The truth is I have no way to prove that the things I believe are real, I simply know they are because I have witnessed them. One of the most common methods of sharing knowledge is the reference to a shared experience. I may describe something, and others will say "Yes that makes sense," have they had the chance to witness the same thing I have witnessed. Although sometimes it gets lost in a difference of how one would use language to describe something. And oftentimes people simply have not witnessed the world around them. Part of why fiction is powerful because unlike philosophy, it does not merely reference a perspective, or crudely recreate the context and then reference it. It can truly recreate what is required for someone to witness something, should that person be perceptive enough to have the ability to witness it in the first place.