Skepticism is a recurring theme in philosophy, but Descartes introduced the theme of radical skepticism, doubts concerning all knowledge. Modern philosophy was a war with partisans on all sides: idealism, materialism, spiritualism, rationalism, empiricism, and so on. This war reached the twentieth century with two camps still obsessed with certainty, Truth with a capital T. The Anglo analytics sought Truth in empiricism and rationality; the postmodernists observed the failure of the analytics to attain it and decided that there was no truth. But notice the loss of the capital T. The failure to find Eternal Truth does not mean that there is no truth. There is still truth in the particular sense: the cat really did sit on the mat. This does not mean that all cats sit on mats, but the particular event is still a fact. There is also truth in the provisional sense: this model of reality is, to the best of our knowledge, true, until contrary evidence disproves it and a better model is found.
Pragmatism took the approach that there is no truth, but we adopt what works. The problem with this approach is that the model that works best is also the most accurate, precisely because accuracy lends itself to unintended uses. A model of reality which simply proved useful would be useful only in those areas which had already been explored or exploited. But truth, by this model, should make technological innovation impossible, simply because there is no reason to assume that such pragmatic solutions, found workable in one application, would be applicable in novel situations. Take our model of the shape of the world. Because the curvature of the earth is so slight (about 0.000126 degrees per mile,) a flat earth was a workable model for farmers, or for navigators on the Mediterranean. To travel to the Americas, navigators needed the model of the world as a sphere. Newton predicted that the world would be an oblate spheroid; there is, in fact, a difference of about 44 kilometers difference between the radius at the poles and the equator. Useful for telemetry of orbits, perhaps, but not for navigation on the ocean. It later turned out that the earth is ever so slightly pear shaped, with a slight bulge in the north. Interesting, but not of much use unless you needed precise positioning down to centimeters.
But as Isaac Asimov remarked in The Relativity of Wrong, "...if you think that thinking the earth is spherical is just as wrong as thinking the earth is flat, then your view is wronger than both of them put together." The accuracy of our model of the world lends itself to novel and unintended results and uses. A purely pragmatic idea of knowledge does not provide for that.
We actually do know things. These may not satisfy the expectations of Truth, but they are true. These truths constitute knowledge, and knowledge narrows the possible. You can believe whatever you like, but you cannot know whatever you like; to actually know something, it must be true. The fact that my pen is on this desk means that it is not in the billions of other places that it could be. Indeed, it is the nature of knowledge to do so, to settle conjecture upon a single point. And this distinguishes knowledge from expression, which is the business of art, and which is as varied as individual experience and opinion. But no truth may contradict another truth. There are not many truths in the postmodern sense; you cannot affirm A & ~A without accepting nonsense and the death of knowledge. There are only many truths in the scientific sense, truths which link together to form a coherent model of the world. And while a model of reality is not reality itself, there is an isomorphic relation between the two. The model maps onto reality in a consistent way.
True, knowledge may consist of knowing someone's opinion of something, or of knowing the contents of mythologies. It is true that Tolkien's elves were immortal, which is of great interest to aficiandos of Tokien's mythology (of which I am one.) But this does not mean that elves exist, and one cannot spin this into knowledge of basic reality. Theology is knowledge of opinion and mythology, and a form of expression, but it must never be confused with knowledge of reality. Mythology tells us nothing about the world. But it does tell us a lot about ourselves.
Human beings are not very good at discovering truth, and are utterly incapable of discovering Truth. We are, however, very good at motivated reasoning; starting with a conclusion, we're very good at coming up with reasons to believe it. This comes in handy in convincing ourselves and others, but to actually figure something out, we need to submit ourselves to the discipline of evidence and peer review. That is, we need to be willing to admit it when we are wrong, and this is not something that comes easily to us. The material world, the world that exists independently of us, is not the world we live in. It is a world we visit with great effort and expense, and rarely at that.
We live in a world of ghosts. Memes are not ideas, nor clusters of ideas, for ideas have no emotive value. Memes have personality; we take them on because they fit into who we are. They are ideas or mannerisms that we like, usually fragments of people that we identify with, and we build ourselves out of these fragments. We live in an ocean of social currents, dreams, metaphors, longings, fantasies, and biases. Stories are a remarkably efficient means of compressing general ideas regarding the social sphere, about what it is to be human and to live with other people. But the creatures of myth are hyperbolic representations of ourselves and others. not real beings or events in the world. By confusing mythology with fact, the faithful lose these deeper meanings. The myths are about us. Science is about the material world, and world we visit only rarely and see only dimly.
We have no talent for cosmology. Our minds are adapted for the middle world, and the scales of the very large and very small are intuitively incomprehensible to us, as anything beyond space and time would be. Mathematics gives us some grasp on scales outside of our core competence, but mathematics without evidence is simply conjecture, and we will never have any evidence of something beyond our own universe--not any evidence that we can understand. Any question that includes "why" talks about intentionality, but intentionality is rooted in time, in the linear and temporal form or intent, followed by action, followed by consequence. To ask why there is something rather than nothing is an attempt to impose social explanations upon the material, and worse, to project intentionality beyond space and time itself, where intentionality as we understand it cannot possibly operate. This is both a category error and a colossal failure of imagination.
If we are actually going to know anything, we have to accept our limitations, and be willing to admit that we don't know when we don't know. This is not an open invitation to fill the void of ignorance with assumptions. To say that we don't know only means that we don't know; it doesn't mean that therefore, X could be true. X could be anything, and to say that anything could be true is the same as saying that nothing is true. We have to be content with our ignorance, and not fill that void with conjecture.