Short answers, pulled from the story.
Epistemology is the branch of philosophy that examines the nature, origin, and limits of knowledge. Also called the theory of knowledge, it studies concepts like belief, truth, evidence, justification, and reason, and stands alongside ethics, logic, and metaphysics as a main branch of philosophy.
The word epistemology comes from the ancient Greek terms episteme, meaning knowledge or understanding, and logos, meaning study of or reason, so it literally means the study of knowledge. Despite these ancient roots, the term itself was coined only in the 19th century to name the field as a distinct branch of philosophy.
According to the traditional analysis, knowledge has three components: it is a belief that is justified and true. In the second half of the 20th century this view was challenged by thought experiments, including Edmund Gettier's counterexamples, showing that some justified true beliefs do not amount to knowledge.
Empiricism holds that sense experience is the primary source of all knowledge, sometimes describing the mind as a blank slate. Rationalism argues that some knowledge, such as mathematical and logical truths, is accessed directly through reason without sense experience.
The often-discussed sources of justification are perception, introspection, memory, reason, and testimony. Perception uses the sensory organs, introspection focuses on internal mental states, memory recalls information from other sources, reason supports non-empirical and inferential knowledge, and testimony relies on what one person communicates to another.
Philosophical skepticism questions the human ability to attain knowledge, and global skepticism asserts there is no knowledge in any domain. Fallibilism agrees that absolute certainty is impossible but rejects the idea that knowledge requires it, concluding that fallible knowledge still exists.