Reading passage
Epistemology, the theory of knowledge, asks what knowledge is, how it is acquired, and whether we possess any at all. For much of the twentieth century the standard answer to the first question was the tripartite analysis inherited from Plato: a person knows a proposition if the proposition is true, the person believes it, and the belief is justified. Knowledge, on this account, is justified true belief, and each condition appears indispensable.
Historically, the discipline was organised around a single great fault line. Rationalists such as Descartes and Leibniz held that the most fundamental truths are known by reason alone, prior to and independently of sensory experience. Empiricists such as Locke, Berkeley, and Hume countered that the mind begins as a blank slate and that all substantive knowledge derives from experience. Immanuel Kant attempted a synthesis, arguing that experience supplies the content of knowledge while the mind's own structures supply its form, so that we can know the world only as it appears to beings constituted as we are, never as it is in itself.
In 1963, Edmund Gettier published a three-page paper that shattered this consensus. He described cases in which all three conditions are satisfied yet the belief is true only by luck. In one famous example, a man has strong evidence that his colleague owns a Ford and reasonably infers that either his colleague owns a Ford or another friend is in Barcelona; unknown to him, the colleague has just sold the Ford, but by sheer coincidence the friend is indeed in Barcelona. The inferred belief is justified and true, yet few would call it knowledge. Gettier problems, as such cases became known, showed that justification, truth, and belief are not jointly sufficient.
Responses to Gettier flooded the journals. Some philosophers proposed a fourth condition, requiring that the justification not depend on any false premise; others demanded that the belief be sensitive to the truth, such that had the proposition been false, the believer would not have held it. Reliabilists, led by Alvin Goldman, shifted attention away from justification altogether, defining knowledge as true belief produced by a reliable cognitive process, much as a well-made thermometer reliably tracks temperature. Each repair, however, generated counterexamples of its own, and some epistemologists concluded that the search for a complete analysis was misconceived.
Beneath these technical disputes lies a darker challenge: scepticism. The ancient sceptic Sextus Empiricus catalogued modes of argument designed to induce suspension of judgment, noting that the same object appears differently to different senses, species, and circumstances, and that any criterion of truth must itself be justified by a further criterion, ad infinitum. Rene Descartes radicalised the doubt by imagining an evil demon of utmost power who might deceive him about everything, including the truths of arithmetic. The modern descendant of the demon is the hypothesis that one might be a brain in a vat, fed experiences by a computer, a scenario popularised by film but sharpened in philosophy by Hilary Putnam.
Anti-sceptical strategies vary in boldness. Descartes himself attempted to found certainty on the indubitable cogito: I think, therefore I am. G. E. Moore simply held up his hand and declared he knew it existed, insisting that common-sense certainties are more secure than any sceptical premise. Ludwig Wittgenstein, in his final notebooks, argued that doubt requires a background of things not doubted, since even the sceptic must rely on the language and practices that make questioning possible. None of these replies has been universally accepted, and scepticism survives less as a position anyone holds than as a permanent audit of epistemic claims.
Recent decades have widened the field's scope. Feminist epistemologists argue that the ideal knower of traditional theory, detached, universal, and disembodied, disguises the situated character of actual inquiry, and that standpoints shape what can be seen. Social epistemology studies knowledge as a collective achievement, examining testimony, trust in experts, and the division of cognitive labour, concerns made urgent by the internet, where anyone may publish and misinformation travels faster than correction. Experimental philosophers have even tested whether intuitions about Gettier cases are universal, finding suggestive cross-cultural variation, though the results remain contested.
The enterprise, then, ends where it began, with questions rather than final definitions. Yet the failure to define knowledge perfectly has not proved paralysing: the long argument has clarified the structure of justification, the ethics of belief, and the conditions under which trust is rational. Epistemology's practitioners increasingly present its problems not as defects to be eliminated but as permanent features of the human cognitive condition, to be understood and managed rather than solved once and for all.