Epistemology — From Greek epistḗmē (demonstrative knowledge) + lógos (discourse). The branch of philosophy investigating the nature, sources, limits, and validity of human knowledge. Although the Greek roots are ancient, the English word “epistemology” was only coined by the Scottish philosopher James Frederick Ferrier in his Institutes of Metaphysic (1854). Its central questions include: what distinguishes knowledge from mere opinion (doxa)? What are the legitimate sources of knowledge — reason, experience, intuition? Is absolute certainty possible? Plato inaugurates the discussion in the Theaetetus, examining (without endorsing) the definition of knowledge as “true opinion accompanied by an account” (logos) — the origin of the traditional analysis of knowledge as justified true belief. In modernity, epistemology polarises between rationalism (Descartes, Leibniz), which grounds knowledge in reason, and empiricism (Locke, Hume), which anchors it in sense experience. Kant effects the critical synthesis: knowledge results from the cooperation between sensory intuitions and categories of the understanding — “thoughts without content are empty; intuitions without concepts are blind”. In the twentieth century, the discipline fragments along several fronts: Popper proposes falsificationism as the criterion of scientific demarcation, Kuhn introduces the theory of paradigms and scientific revolutions, Quine defends epistemological holism, and Gettier (1963) unsettles the classical analysis with counterexamples that exhibit cases of justified true belief that fail to count as knowledge. It is distinguished from ontology (the study of being) and is closely related to gnoseology and the philosophy of science.
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