Knowledge

Knowledge Plot Summary

Introduction

What exactly is knowledge? This question has fascinated philosophers for thousands of years. When you claim to know something—whether it's what you had for breakfast this morning or the capital of France—what are you really asserting? In our digital age, answers to factual questions are more accessible than ever, yet distinguishing genuine knowledge from mere opinion or false information remains challenging. We constantly make judgments about what we and others know, often without reflecting on the nature of knowledge itself. Epistemology, the branch of philosophy dedicated to studying knowledge, tackles fundamental questions about how we know what we know. What separates knowledge from mere belief? How does knowledge relate to truth? Is knowledge objective or subjective? This book explores these questions, tracing the development of epistemological theories from ancient skeptics who questioned the possibility of knowledge to contemporary debates about the social aspects of knowing. Along the way, we'll examine different approaches to knowledge—rationalism versus empiricism, internalism versus externalism—and consider how testimony from others shapes what we can claim to know. By the end, you'll have a clearer understanding of what philosophers mean when they talk about knowledge and why the concept remains central to how we navigate our world.

Chapter 1: The Hunt for Knowledge: Defining What We Can Know

Knowledge might seem straightforward at first glance—we use the word "know" frequently in everyday conversation without much difficulty. Yet philosophers have struggled for centuries to provide a precise definition. One key insight is that knowledge always involves a relationship between a knower and what is known. Unlike physical resources such as water or gold that would exist regardless of whether humans perceived them, knowledge requires a mind to grasp it. Facts only become knowledge when someone has access to them. This connection between knower and known helps explain a fundamental feature of knowledge: it has a special relationship with truth. You can believe something false, but you cannot know something false. Consider the difference between saying "Jill knows her door is locked" versus "Bill thinks his door is locked." If Jill knows her door is locked, then her door must actually be locked—otherwise, we would have to retract our claim that she knew. Philosophers call this feature "factivity"—knowledge can only be of facts or true propositions. By contrast, Bill might think his door is locked even when it isn't. However, truth alone isn't sufficient for knowledge. If you guess the correct answer on a multiple-choice test without studying, you don't really know the answer even though your belief is true. Similarly, if a father believes his daughter is innocent of a crime purely out of parental love rather than based on evidence, his belief might happen to be true but wouldn't count as knowledge. Knowledge seems to require some appropriate connection between the truth and our belief in it. Different philosophical traditions have offered competing accounts of what makes a true belief count as knowledge. Some emphasize the role of justification—having good reasons or evidence for what you believe. Others focus on reliability—whether your belief was formed through processes that typically lead to truth. Still others consider factors like whether your belief tracks the truth across different situations or whether you can rule out relevant alternatives to what you believe. What makes the study of knowledge particularly fascinating is how it connects to broader questions about human nature and our place in the world. Are our minds equipped to grasp reality as it truly is? Can we transcend our limited perspectives to achieve objective knowledge? These questions have practical implications for science, education, law, and everyday decision-making. Understanding what knowledge is helps us better evaluate our own claims to know things and judge when to trust the knowledge claims of others.

Chapter 2: Skepticism: Can We Know Anything at All?

Skepticism represents one of philosophy's oldest and most persistent challenges, questioning whether genuine knowledge is even possible for humans. The skeptic invites us to consider scenarios that seem to undermine our confidence in what we believe we know. Could you be dreaming right now as you read these words? If so, your apparent knowledge about your current state might be illusory. How can you prove conclusively that you're not in a dream? Any test you devise—like pinching yourself—could itself be part of the dream. Ancient Greece produced two distinct skeptical traditions. Academic Skeptics, led by philosophers like Arcesilaus and Carneades, argued positively for the conclusion that knowledge is impossible. They challenged the Stoic view that knowledge comes from accepting only impressions that couldn't possibly be wrong, contending that even our most vivid impressions might be mistaken. Pyrrhonian Skeptics, following Pyrrho of Elis, took an even more radical approach. Rather than asserting that knowledge is impossible, they aimed to suspend judgment on all questions, including whether knowledge is possible. Pyrrhonians developed techniques for balancing opposing arguments, believing this practice led to peace of mind. Throughout history, skepticism has resurfaced during periods of intellectual upheaval. In the 16th century, as new scientific discoveries challenged medieval worldviews, thinkers like Michel de Montaigne embraced skeptical doubt. René Descartes later developed his famous method of systematic doubt, imagining an evil demon dedicated to deceiving him at every turn. While Descartes himself used skepticism as a starting point toward establishing certain knowledge, his vivid skeptical scenarios continue to influence philosophical thought. Modern responses to skepticism take various forms. G.E. Moore famously confronted skepticism about the external world by simply holding up his hands and declaring, "Here is one hand, and here is another." Moore argued that our everyday certainty about such matters is more reasonable than the skeptic's abstract doubts. Other philosophers have suggested that the simplest explanation for our experiences is that they're caused by a real external world, making skeptical scenarios unnecessarily complicated. More recently, some have argued that the skeptic's hypotheses are self-defeating—if we were brains in vats stimulated by computers, our words wouldn't even refer to real brains or vats, making the skeptic's claim unintelligible. What makes skepticism so enduringly powerful is that it begins with the reasonable observation that our beliefs can sometimes be wrong and pushes this insight to its extreme conclusion. Even if we reject total skepticism, engaging with skeptical arguments helps clarify what knowledge requires and how far our claims to know can legitimately extend.

Chapter 3: Rationalism vs Empiricism: Sources of Knowledge

How do we acquire knowledge? Rationalism and empiricism represent two competing answers to this fundamental question, with their roots in the Early Modern period (roughly 1600-1800). This era marked a dramatic shift in humanity's understanding of nature and knowledge itself, as thinkers moved away from medieval approaches that saw reality as a symbolic work centered on human beings toward more mathematical and observational methods of understanding the world. Rationalism, powerfully articulated by René Descartes, places abstract reasoning at the heart of knowledge. Descartes famously began his philosophical project by doubting everything he could possibly doubt, eventually finding certainty in his own existence: "I think, therefore I am." From this foundation, he rebuilt knowledge through clear and distinct ideas that he believed were innate—built into the human mind by a benevolent God. According to Descartes, our most trustworthy knowledge comes not from sensory experience, which can deceive us, but from the rational intellect. Mathematical and geometrical truths exemplify this kind of knowledge—you can know with certainty what a triangle is without ever seeing a perfect triangle in nature. Empiricism, championed by John Locke, takes the opposite approach. Locke rejected the notion of innate ideas, arguing that the mind begins as a "blank slate" (or "white paper") that gains knowledge through experience. "Nothing is in the intellect that was not first in the senses," empiricists maintained. According to Locke, our simple ideas come from two sources: sensation of external objects and reflection on our own mental operations. We then combine these simple ideas to form more complex concepts. While Locke acknowledged that we could gain certain knowledge of mathematical and logical truths, he maintained that such knowledge still ultimately depends on ideas received through experience. The contrast between rationalism and empiricism reflects different perspectives on human knowledge. Descartes approached epistemology from a first-person perspective, asking "What can I know for certain?" and focusing on what can be known through introspection alone. Locke more readily adopted a third-person perspective, examining how humans generally acquire knowledge through interaction with their environment. These different starting points led to different conclusions about what we can know and how we know it. Both approaches contributed important insights to our understanding of knowledge. Rationalism highlights the power of abstract reasoning and mathematical thinking that transcends particular experiences. Empiricism emphasizes the crucial role of observation and sensory data in building our understanding of the world. Modern epistemology has worked to integrate these perspectives, recognizing that knowledge typically involves both rational reflection and empirical observation working together, though debates continue about their relative importance in different domains of knowledge.

Chapter 4: The Gettier Problem: Beyond Justified True Belief

For centuries, philosophers analyzed knowledge as justified true belief. On this view, you know something when: (1) it's true, (2) you believe it, and (3) you have adequate justification for believing it. This seemed to capture our intuitions about knowledge—truth is necessary (you can't know falsehoods), belief is necessary (you can't know something you don't believe), and justification distinguishes knowledge from lucky guesses. This tidy analysis remained largely unchallenged until 1963, when Edmund Gettier published a remarkably short paper that revolutionized epistemology. Gettier presented scenarios where someone has justified true belief but intuitively lacks knowledge. Consider a classic "Gettier case": Smith glances at a station clock that reads 1:17 and forms the belief that it's 1:17. His belief is true (it really is 1:17) and justified (checking reliable clocks is a reasonable way to tell time). However, unknown to Smith, the clock is broken and has been stopped at 1:17 for days. Smith just happened to look at the broken clock at exactly the time it displayed. Does Smith know it's 1:17? Most people intuitively say no—his correct belief seems too accidental to count as knowledge. Philosophers initially thought they could easily fix the justified true belief analysis by adding a fourth condition. Some suggested that knowledge requires that your justification not depend on any false beliefs (Smith falsely believes the clock is working). But counterexamples emerged showing this approach wouldn't work. Sometimes people can have knowledge despite having some false supporting beliefs, and other times people can lack knowledge even without any false beliefs in the picture. The Gettier problem proved surprisingly resistant to simple solutions. Alternative analyses of knowledge were developed in response. Alvin Goldman proposed a causal theory, suggesting that knowledge requires an appropriate causal connection between the fact known and the believer's state of mind. On this view, Smith lacks knowledge because his belief about the time isn't caused by the actual time but by the coincidentally correct broken clock. Goldman later developed this into reliabilism, which holds that knowledge is true belief produced by reliable processes—processes that generally yield true beliefs. Robert Nozick offered a tracking theory, suggesting that knowledge requires beliefs that "track the truth" across different possible situations. After decades of increasingly complex proposals, some philosophers began to wonder whether knowledge could be analyzed at all. Timothy Williamson suggested that knowledge might be a fundamental concept, more basic than belief rather than built from belief plus other factors. On this "knowledge first" approach, we should explain believing as a kind of approximation to knowing, rather than explaining knowing as a special kind of believing. The Gettier problem thus led epistemologists to reconsider basic assumptions about the nature of knowledge itself.

Chapter 5: Internalism and Externalism: Perspectives on Knowledge

Imagine trying to defend your claim that Mount Everest is the tallest mountain in the world. Could you provide compelling evidence or reasons? If pressed, many people would struggle to explain exactly how they know this fact—they might say it feels familiar or that they learned it in school, but they couldn't cite specific measurements or sources. This scenario highlights a fundamental debate in epistemology between internalism and externalism about knowledge. Internalists maintain that knowledge requires having access to adequate justification from your own first-person perspective. According to internalism, if you can't access any reasons supporting your belief about Everest, then you don't really know it—you just have a belief that happens to be true. Knowledge, on this view, involves being able to see for yourself why you should believe something. The justification must be "internal" to your conscious awareness or at least accessible through reflection. This approach emphasizes the knower's rationality and ability to provide reasons for what they believe. Externalists argue that knowledge doesn't always require this kind of first-person access to justification. What matters instead is that your belief is connected to the truth in the right way, even if you can't articulate or access that connection yourself. For example, a reliable memory might give you knowledge even if you can't recall exactly how you learned something. On externalist views, knowledge is a relationship between a person and a fact that can be present even when the person can't explain the relationship. The factors that make a belief knowledge might be "external" to the knower's conscious awareness. These competing perspectives lead to different verdicts about specific cases. Consider Laurence BonJour's example of Samantha, who believes she has clairvoyant powers to detect the U.S. President's location. She has no evidence supporting this belief and even has contrary evidence (news reports showing the President elsewhere). Yet imagine that: (1) the President really is where Samantha believes, (2) the news reports are fabricated, and (3) Samantha actually does have reliable clairvoyant powers. Externalists might say Samantha knows the President's location since her belief is true and formed through a reliable process. Internalists would deny this is knowledge because Samantha lacks good reasons from her perspective. The internalism-externalism debate connects to deeper questions about the nature of rationality and the role of perspective in knowledge. Internalism captures the intuition that knowledge involves seeing the truth for oneself, while externalism captures the intuition that small children and unreflective adults can have knowledge despite being unable to articulate their justifications. The debate continues to be central in epistemology, with many philosophers seeking positions that incorporate insights from both approaches while avoiding their respective weaknesses.

Chapter 6: Testimony: Learning from Others

Much of what we believe to know comes not from direct experience or personal reasoning but from the testimony of others. You likely believe that Antarctica exists, that George Washington was the first U.S. president, and countless other facts that you've never verified personally. Our dependence on testimony raises important philosophical questions: When does hearing something from someone else provide you with knowledge? Do you need special reasons to trust people before you can gain knowledge from them? How should we evaluate sources like textbooks, news reports, or Wikipedia articles? Philosophers have advanced several competing views about testimonial knowledge. At one extreme, John Locke argued that testimony never actually provides knowledge. Locke distinguished between perceptual knowledge (like directly seeing that a voice is hoarse) and what we get through testimony (like being told about an event). He claimed that while testimony might provide highly probable beliefs, it lacks the certainty required for genuine knowledge. On Locke's view, you don't strictly know where you were born if your belief is based solely on what your parents told you—you merely have a highly probable opinion. A more moderate position, reductionism, holds that testimony can provide knowledge, but only when supported by other sources like perception, memory, and inference. Global reductionists claim we have general inductive evidence that testimony is usually reliable, based on our past experiences of verifying what others tell us. Local reductionists maintain that we need specific reasons in each case to trust a particular speaker on a particular topic. Both types of reductionism see testimony as deriving its epistemic force from more basic sources of knowledge. The most generous approach, sometimes called the "direct" or "default" view, treats testimony as a basic source of knowledge in its own right. On this view, understanding what a knowledgeable speaker says is sufficient for gaining knowledge, without needing additional reasons to trust them. This approach, defended by both classical Indian philosophers and many contemporary Western thinkers, emphasizes that trust in testimony is fundamental to human communication and learning. Even children who lack the capacity to evaluate sources can gain knowledge through testimony, as when they learn the meanings of words. All views acknowledge certain conditions on testimonial knowledge: what you're told must be true, and usually the speaker must know it too. A lawyer who convincingly argues his client is innocent without believing it himself typically doesn't transmit knowledge to the jury, even if the client happens to be innocent. However, some philosophers argue that groups working together (like Wikipedia editors) might produce knowledge collectively that no individual member fully possesses. As our information sources become increasingly complex and collaborative, understanding how testimony transmits knowledge becomes ever more important.

Chapter 7: Context and Standards: When Knowledge Shifts

Does the meaning of "know" stay fixed across different conversations, or might it shift depending on context? Consider these scenarios: Lee tells a colleague that he knows the supply room door is locked because he locked it himself half an hour ago. Later, when police ask if he knows the door is locked during an emergency, Lee says he doesn't know—he wasn't watching the door continuously. In both cases, Lee's evidence is identical, yet his knowledge claims differ. What explains this discrepancy? Contextualism in epistemology holds that the word "know" is context-sensitive, similar to words like "tall" or "here" whose meaning varies with context. Just as a six-foot man might be considered tall in everyday contexts but not tall among basketball players, a person might count as knowing something in everyday contexts but not in contexts where more is at stake. According to contextualists, both of Lee's statements can be true because the standards for knowledge rise in the high-stakes police conversation. Contextualism promises to reconcile our everyday confidence in what we know with the skeptic's doubts—both are right in their respective contexts. Not everyone accepts contextualism. Interest-relative invariantism (IRI) agrees that practical stakes affect knowledge, but maintains this happens because knowledge itself varies with practical interests, not because the word "know" changes meaning. On this view, Lee genuinely knows in the low-stakes conversation but genuinely lacks knowledge in the high-stakes situation. What you need to know depends partly on what's at stake for you, with higher stakes requiring stronger evidence. The difference between contextualism and IRI is subtle but significant: contextualism is a theory about language, while IRI is a theory about knowledge itself. Other philosophers defend strict invariantism, maintaining that neither language nor knowledge varies with context. Strict invariantists come in two varieties: skeptics who set the bar for knowledge extremely high (so Lee never truly knows in either case), and moderate invariantists who set it lower (so Lee knows in both cases, despite what he says to the police). Moderate invariantists must explain why people like Lee deny knowledge in high-stakes situations—perhaps due to confusion or a desire to avoid making strong claims when the consequences matter. The debate about context-sensitivity in knowledge claims connects to deeper questions about the purpose of our concept of knowledge. Is knowledge primarily about tracking truth regardless of practical concerns, or does it function partly to mark when we have enough evidence to act? Our shifting intuitions about knowledge cases suggest that practical concerns do matter to our judgments, but philosophers continue to debate whether these shifts reflect features of knowledge itself or merely how we talk about it.

Summary

At its core, knowledge represents a distinctive relationship between minds and reality. Throughout this exploration, we've seen how philosophers have attempted to define this relationship—from the ancient skeptics who questioned its possibility, to rationalists and empiricists who debated its sources, to contemporary thinkers who examine its social dimensions and contextual features. The Gettier problem revealed that knowledge cannot be simply reduced to justified true belief, while debates between internalists and externalists highlighted different perspectives on what makes belief into knowledge. Even as we rely on testimony from others for most of what we claim to know, questions persist about when such reliance is justified. What emerges from these investigations is that knowledge occupies a special place in human understanding—neither a mere subjective opinion nor an impossible ideal of perfect certainty. Rather, knowledge represents our best effort to grasp reality in a way that guides action and supports further inquiry. The philosophical journey through epistemology doesn't end with final answers but opens new questions: How does knowledge function in scientific communities? How should we evaluate competing knowledge claims in a complex information landscape? How do power and privilege affect who gets to claim knowledge? For those intrigued by these questions, the philosophy of knowledge offers not just theoretical interest but practical guidance in navigating an increasingly complex world where distinguishing knowledge from its counterfeits matters more than ever.

About Author

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Jennifer Nagel

Jennifer Nagel (b. 1947), Canadian philosopher.

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