Epistemology is the school of philosophy containing the theories about the structure of knowledge and reason. As an understated, misrepresented and much misunderstood field, epistemology is actually at the heart of every philosophy and science because it explains how you might come to know anything with any certainty.
Essentially every bit of knowledge or belief is an idea or a concept about “reality.” The materialist interpretation of Rene Descartes led to the “standard scientific method,” the greatest stumbling block of post-modern science like quantum and string theory. Materialist science alludes us to believe that everything is separated (not unified) and that reality is something that exists “out there” completely independent of the observer and yet we find that reality is covertly dependent on personal cognition, “observation,” experience and sensory perception for it to “exist.”
You accept knowledge that you cannot personally verify outside of the conception or paradigm and use of language that was specifically created to identify and prove the very knowledge in question.
French philosopher Rene Descartes (1596-1650) can be credited with offering the most significant modern contributions to epistemology, primarily founded by him as a generalist philosophy of all “modern” scientific thought. In the entirety of his works, only a few simple key tenets stand out distinctly, though thousands of words and multiple essays were composed to offer explanations and clarification to the era he was writing for.
As described in the original essay by Joshua Free:
In “Discourse on the Method of Rightly Conducting the Reason and Seeking Truth in the Sciences” (1637) Descartes describes an intensive process by which the operator must attempt to clean their slate of knowledge of all that can be doubted, which proves to be essentially everything determined through sensory perception and physical experiences. These things can then be added back into a personal paradigm after vigorous scrutiny and in the logical order of certainty. First and foremost is self-knowledge, proved by the self-aware consciousness of an individual; then God, the perfect encompassing generative force in the Universe; and finally mathematics and geometry, the means in which one might measure and quantify existence in the Universe. Mathematics, however, will necessarily loop the seeker back to contemplation on the interpretive use of symbols and language. Descartes even illustrates that as a model of observable (empirical) materialist science, even if we are certain of what our senses tell us about a causal “how,” no absolute knowledge of the “why” can be determined the same way.
Perhaps the least cited, but most concise, discourse from Descartes is “Principles of Philosophy” (1644). The work composes over one hundred propositions, each with an explanation, as well as significant axioms and other clarifications of his unique paradigm. Though the title might suggest some all-encompassing resolution or textbook, this slim volume actually reduces philosophy into two main aspects: the nature of human knowledge (epistemology) and the nature of material existence and reality (metaphysics). The concept is put forth that the senses deceive and all that we can determine of the material world is accessed by material senses and then processed cognitively. Anything beyond the material, or “metaphysical,” which includes our cognitive faculties and the mind-body connection, cannot be determined with the material senses and therefore lies outside of the domains of “empirical” science. Hence, a development in the “meta-sciences” that will take into account the “spiritual” and other alternate levels of existence.