foreign [Music] pause for a moment and conjure up in your mind something that you know for certain, an indisputable fact: rain comes from clouds, your mother's first name, swans are white, God is real. Then consider, how is it that I know this fact? Am I depending on my senses to confirm something is true? Are they completely trustworthy? Did I rely on someone else to tell me this information? Who told the person who told me? Ask yourself, what does it mean to really know something? How can I know that I know it? When can I be completely confident that my beliefs about the world are justified? Is seeing the same thing as believing? Suppose there's a vase on a table, and I look in the direction of the vase, but interposed between me and the vase is a very, very well-drawn picture of a vase or a hologram of a vase. And what I actually see is that picture or the hologram. So I look in that direction, there's a vase in that direction, and I come to believe on the basis of looking

at the picture that there is a vase. My belief that there's a vase in that direction is true because there is one, and I certainly believe it strongly enough. And I think if you ask me, do I know that there's a vase there, I'd say yes. On the other hand, it's quite clear I'd be wrong in saying that. What can be said about a vase can be said about virtually every other aspect of the world we live in. The philosophical study of the nature and the scope of what we can know is called epistemology. [Music] There are two primary questions that epistemology addresses. First, what, if anything, do instances of knowledge have in common? In other words, what is the nature of knowledge? And second, what is its scope? The answer to these questions has tremendous social implications. [Music] How can we know for certain someone is guilty before we send them to prison or even to their deaths? Do scientists push the envelope of knowledge, or are they fabricating it as they go? [Music] We rely on knowledge to weave the

tapestry of our daily lives, but how dependable is what we take to be knowledge? We rely on newspapers, we rely on the internet, we rely on all of these things, but how are these things organized, and how do people get the sources of information that they get? Now, we all know that in totalitarian situations, people are exposed only to sources of public information that have been approved of by dictators who choose those and restrict these sources to serve their own ends. The first question that epistemology must confront is what we mean when we claim to know something. I think we would say that the automatic door opener at a grocery store knows when somebody is approaching because it opens. I think we might even say that one animal knows when another animal has been there by a sense of smell. On the other hand, we want to say Newton knew the law of gravitation, and one of the questions is, is there any common notion of knowledge that would cover all of those cases? The human quest to define what we know.

and how we know it begins at the beginning with the classical Greek philosophers. [Music] Public Plato examined the very pragmatic issue of how it is that people could lead good lives, and it is this seemingly straightforward question that led him to explore the very headwaters of knowledge. [Music] To emphasize that what we know must not be acquired by mere accident, Plato gave an analogy in which he compares knowledge to the work of a highly skilled artist. Daedalus was a sculptor who could make semi-magical statues. When you approach them, they would run away, and what Plato asks is this: why do we so highly prize knowledge? What is it about knowledge that is so desirable? It's much more desirable than just mere true opinion or true belief. Now, why is that? And out comes the analogy. The analogy is knowledge is tethered true belief. We want the statues not to run away. We want our true beliefs not to want to run away. We want them to be founded upon something permanent. [Music]

public also contains Plato's famous allegory of the line. He asserted that knowledge can be understood as a vertical line divided into two unequal segments, each of which is itself made up of two unequal parts. The lower portion of the vertical line represents knowledge received through the senses, that is, opinions or beliefs. The realm of the senses is further divided into perceptions of visible objects in this world on the one hand, and images and reflections of those objects on the other. As mere copies of what exists, images and perceptions are the lowest forms of knowledge. The upper portion of the vertical line represents the intelligible world, the world of what Plato called the ideas or forms, the true essence of reality. This world can't be reached by the senses; it is only accessible to reason. Here, there is another division between provisional or incomplete knowledge on the one hand, and the complete knowledge of the forms on the other. Episteme, true knowledge, only comes at this highest level, where what is true and what is real become one. Much of what we now deal with under the

concept of Truth Versus Falsehood. Plato will deal with under the rubric of authentic versus fake, and that that is a serious difference in a way in both metaphysics and philosophy or language and epistemology. In his allegory of the cave, Plato gave one of the most compelling accounts of the relationship between truth and authenticity. Plato said, Imagine a cave in which people are tied down so that they can't see behind them. They can only look ahead at the back wall of the cave. Behind them are others standing behind a ledge. These people hold puppets over the ledge, find the puppeteers. There is a fire whose light is projected onto the back wall of the cave. The prisoners see the shadows of the puppets, but since that's all they know, they think these shadows are reality, the essence of the world. In fact, not only are the shadows not real, but the puppets themselves are not real. [Music] Our own account signifies that the soul of every man does possess the power of

learning the truth and the organ to see it with. And that just as one might have to turn the whole body around in order that the eye should see light instead of darkness, so the entire soul must be turned away from this changing world until its eye can bear to contemplate reality and that supreme splendor which we have called the good. Aristotle was Plato's main student and often his most penetrating critic. He came to reject Plato's forms, which he felt were nothing more than abstractions of actual things. For Aristotle, individual and particular entities are the only concrete reality, and true knowledge is gained through intuition and experience. We know the idea of a triangle by abstracting common characteristics from the triangles we have seen in our daily lives. Aristotle claimed that what ultimately is real is not ideas or forms, but rather individuals. Aristotle believes that human beings are generally endowed with the abilities to understand the world around them more or less completely. Some of us are better at it than others, but where Plato would see

people are divided into different classes according to their abilities. Thinks it's only a matter of degree, rather a matter almost like the kind of person. Actual knowledge is identical with its object in the individual. Potential knowledge is in time prior to actual knowledge, but in the universe as a whole, it is not prior even in time. [Music] One attribute that the epistemologies of Aristotle and Plato have in common is that they both seek out the bedrock upon which knowledge can be built. In their view, reasons for believing something to be true rest on a structure of basic beliefs known as foundational propositions, which do not derive their justification from other propositions. This view is called foundationalism. The main challenge to foundationalism, first articulated by the Greek philosopher Pyrrho of Elis, is how do you know when you've struck bedrock? At what point does the chain of reasons stop? Which reasons are true in and of themselves? [Music] Brilliance thought, Okay, we get back to this foundational proposition, and then I ask you, why do you think that one's true?

and you say, Well, I don't have any reason for that one. Uh, and in fact, you go even further and you say, I don't need a reason for that one. Don't you see this is foundational? And then the interlocutor can say, Okay, I see you think this proposition is true, but you don't need a reason for it. Is there something about this proposition which is such that propositions of that sort are true even though you don't have a reason for them, that you're entitled to assert them even though you don't have a reason? And you'll probably say, Well, yes, they're describing my sense experience, you might say, or you might say, 'Yes, they're describing mental states to which I have access, like pain.' And what the Peronian will do is to say, Well, do you think that you have infallible access to your mental states or to your sensations? And either you can say yes or you can say no. [Music] If you say yes, then the chain of reasons stops, but this stopping point is itself

arbitrary and can't support any subsequent links. If you say no, then your chain of reasons is infinitely long, in which case you have an infinite regress, and your belief isn't justified by a foundational proposition. [Music] If the chain goes in a loop, then you have a circular argument. Anywhere you go, you hit a brick wall. You are stuck in epistemic regress, and the view that this stuckness is unavoidable is called skepticism. The most fundamental problem about knowledge we can raise is where does the buck stop, or does it just keep going? [Music] Skeptics saw that opposing arguments often seem to carry equal weight and believe that the search for truth was an unending process. While this may seem a distressing conclusion, their goal was actually to achieve Tranquility of Mind by suspending judgment altogether. They rejected Dogma in all its forms, and Skeptics since the time of Pyrrho have believed that all philosophical systems are suspect because they far exceeded the limits of what can be known.

the main basic principle of the skeptic system is that of opposing to every proposition an equal proposition, for we believe that as a consequence of this, we end by ceasing to dogmatize. Despite the power of their arguments, the Skeptics fail to wipe out foundationalism, and it continues to be the most commonly held epistemological view. Foundationalism can take many forms, such as empiricism, the belief that knowledge is gained through the senses, or rationalism, which holds that some kinds of knowledge are innate. The French philosopher René Descartes, founder of the rationalist school, believed that certain fundamental ideas reside within our souls from birth, such as the first principles of mathematics. The world, for Descartes, begins with the self; all else is subject to doubt. The self, now in Descartes' philosophy, is going to be the beginning of an entire reconstruction of the world. Of course, we know where it's going; it's going toward this mechanistic view of the world. Descartes believes that everything can

be explained in terms of side shape and motion and in terms of the Soul, which is the self, the beginning place of the reconstruction. Um, this was philosophically, of course, an important Revolution, and Descartes had many, many followers. Thank you, though. Descartes is renowned for doubting things, from sensory experiences to his own existence. His form of Doubt was different in kind from classical skepticism. A way to think of the difference between the Pyrrhonian and Cartesian skeptic with regard to the claim we do have knowledge is the Cartesian skeptic denies it, says we don't have knowledge. The Pyrrhonian says it's not clear to me whether we do have knowledge or we don't have knowledge, and so the Pyrrhonian would not consider the Cartesian skeptic a skeptic at all. According to Descartes, something known by the natural light of Reason cannot be false. [Music] What leads to error is not a lack of reason but rather a lack of method. If mathematics has made great progress, if logic is beyond reproach, if physics has exposed the mysteries of

the universe. Then it is because human reason is capable of knowing the world around us. The Skeptics were wrong; with a good method and enough time, there can be no secrets kept from rational inquiry. But among these ideas, some appear to me to be innate, others advantageous, and others to be made by myself, factitious. For as I have the power of conceiving what is called a thing or a truth or a thought, it seems to me that I hold this bar from no other source than my own nature. Descartes places a great deal of emphasis upon abstract reasoning abilities and little emphasis on the role of the senses or even denigrates the role of the senses, whereas Francis Bacon and many who followed him in Great Britain place much more emphasis upon the role of the human senses as the fundamental source of input and treat reason as a subsidiary faculty that largely just organizes the material of the senses. Francis Bacon was an early champion of empiricism, putting his faith in the

senses as a solid foundation for knowledge. The three major empiricists were all English: John Locke, George Berkeley, and David Hume. Though their views diverged greatly, they each emphasized the fundamental comprehensibility of the world. They thought of the senses as yielding impressions or ideas in the mind, where these were what we would know, like visual appearances, something looking a certain color and looking to be a certain shape. And they conceived of these data of sense to be states of the mind or objects that are before the mind and in the mind. John Locke was an enemy of tyranny in all its forms and vehemently opposed Descartes' notion of innate ideas. Locke argued that if general truths such as logical and mathematical principles were intrinsic, then a child would know them without needing to be taught. Because it is devoid of innate ideas, the human mind is like a blank sheet of paper that is written upon by experience. According to Locke, an idea is any representation we have in our minds. What we have to do is work with experience and generalize from

experience, and because of that, there are things that we can never know, and there are other things that we can know only imperfectly, only to the extent to which experience reveals them to us. Follow a child from its birth and observe the alterations that time makes, and you shall find, as the mind by the senses comes more and more to be furnished with ideas, it comes to be more and more awake, thinks more the more it has matter to think on. If it shall be demanded then when a man begins to have any ideas, I think the true answer is when he first has any sensation. The Irish clergyman George Berkeley was the next in line of the great English empiricists. Like Locke before him and Hume after him, Berkeley put his faith in the experience of the senses, but then they faced also the problem of how can I go from what is in the mind to what is out there outside the mind in the physical world, and they saw there was a problem, and especially Berkeley saw there was a problem, and his

move was very radical, so he saw no way of making an inference from the ideas in the mind to something completely different from ideas. So, he said, actually, what other people call the physical world, that extra, that's external to the mind. He said that all of it really resides in the mind, that chairs and tables and all those things that we think of as physical are really things that exist in the mind. [Music] The Scottish philosopher David Hume took empiricism to its logical extreme. According to Hume, perception is any representation we may have in our minds. [Music] There are two kinds of perceptions: Impressions, which are strong and clear, and ideas, which are weak copies of impressions. For example, seeing the color red is an impression, and remembering or imagining it is an idea. Every impression leaves its trace in the form of an idea, and every idea can be traced back to an impression. So, one kind of impression are sensations, and Hume would take those to be basic trace your justification back to impressions. And once you've done so, you

can't go any further, and so you've completed this kind of regress, so you're back to the foundational proposition. Um, another source of impressions for Hume, not impressions of the external world, but impressions of my own state. So, I feel a pain, for example, or I'm feeling happy. Those are impressions, but internal impressions, impressions of myself, so to speak, so impressions of the mind itself. And again, so you could trace your justifications back to impressions of that sort, and then it's not, there's no point in going further, Hume would say. You couldn't go further. The mind is a kind of theater, wrote Hume, where several perceptions successively make their appearance. [Music] Hume believed that impressions can be either simple or complex. A color, for example, is a simple impression, but an object such as an apple produces a complex impression because it involves other dimensions of experience as well, such as shape, taste, and so on. An idea may also be either simple or complex. Many complex ideas don't begin with experience but rather are the result of

combining together in the imagination simple or complex ideas which do come from experience. Hume called the relating of ideas in the mind Association. Association may be of three kinds: resemblance, contiguity, and causality. When we look at somebody's picture and think of the person in that picture, that is resemblance. If we see a roof from a window and assume there is a house there, not just a roof, that is contiguity. Our expectation that certain events will always follow other events is causality. So suppose I take this pen out of my pocket, and I open my fingers, and it drops, and I do that over and over and over again, and I come to believe that opening my fingers is a sufficient cause, given the way the world is, for the pen to drop. So I come to believe not only um has it dropped in the past, it's going to drop in the future. The human will say, Look, is it conceivable that the pen not drop? Could you imagine the pen not dropping? And yes, I could. I could imagine it not

dropping, so it isn't a priori that the pen is going to drop. It's certainly true you anticipate the pen dropping, but Hume will say, Do I have any reason for thinking that if I open my fingers, the pen will drop? Hume held that the idea of causation boils down to the impression of anticipation that we have after repeatedly experiencing the succession of one type of event following another. While we may conjoin everyday occurrences in our minds—lightning causes thunder, viruses cause disease—the necessary connection between cause and effect can't be established. Come on. [Music] When we look about us towards external objects and consider the operation of causes, we are never able in a single instance to discover any power or necessary connection, an equality which binds the effect to the cause and renders the one an infallible consequence of the other. We only find that the one does actually, in fact, follow the other. [Music] While we may anticipate events to follow in a sequence, we can have no knowledge of a necessary

connection between them that we can't relate effects to causes in creating theories about the world. If so, then what becomes of science, one of our most impressive forays into epistemology? [Music] The task of reconciling human skepticism with Cartesian subjectivity and, in effect, making the world safe for knowing again, fell to an unassuming Prussian philosopher named Emmanuel Kant. He believed that we all share certain frameworks for understanding the world, which are real in that they exist in the context of our minds. Kant put the mind in a different relation to reality than any of his predecessors. This is um. His predecessors had uh thought of the mind as a passive observer of reality and had sort of looked around for some kind of guarantee that it was a good passive observer of reality. Prided himself on what he called the Copernican revolution in philosophy, the idea that uh that actually the mind structures the way reality can appear to us, and then in the sense reality has to conform to the laws of the mind rather than the mind trying to

to discover what reality laws of reality are, which are completely external to it. Unlike Hume, can't believe that scientific knowledge is universal and necessary, not simply probable, but it is a kind of universality and necessity that lies within the world of phenomena. Whether it exists in the world in itself doesn't matter because we can't truly know anything besides the contents of our own minds. Human reason has this peculiar fate that in one species of its knowledge, it is burdened by questions which, as prescribed by the very nature of Reason itself, it is not able to ignore, but which, as transcending all its powers, it is also not able to answer. At the beginning of the 20th century, there began a revolution in philosophy that became what is now known as analytic philosophy. The English philosopher Bertrand Russell was at the forefront of this revolution. Russell claimed that knowledge is an overly vague term since it must include both human and animal knowledge, and within human knowledge, it must include both everyday and scientific knowledge. Russell's colleague G.E. Moore held a

common sense view of knowledge. He believed that the being of a thing is independent from the knowledge we may have of it. Consciousness only reflects what is real. Cartesian skepticism about the external world simply isn't justified. So, elemental proofs that were monumentally difficult for Descartes, proving that your hands exist, for example, were for more simplicity itself. So, how do I prove that there are hands according to Moore? This way: here's one hand, here's another. I just proved that there were two hands. What more do you want? Um, this is a view in philosophy called direct realism. Direct realism, in this sense, Moore thinks that I can know things through perception without being able to prove them. In other words, I don't need an argument to know everything. It is a kind of foundationalism, foundationalism that says, Look, you want to know whether there are hands? How do you do that? You open your eyes and you look. You don't give an argument for the claim that there are hands. The Austrian philosopher Ludwig Wittgenstein was an early pioneer in the

rigorous analysis of language in philosophy. He attempted to move the concept of meaning from the fact or object represented by words to the use given to those words by a particular community. As language only acquires meaning when employed by people, any link between a given word and its object depends on the rules set by those who use that word. These rules define what Wittgenstein called language games. He believed that all of us who engage in the same language game employ hears a hand as a bedrock proposition, one which cannot under ordinary circumstances be doubted because that is a fact about the language game itself. Wittgenstein and other philosophers whom he influenced felt that philosophical questions are a matter of language, and it's a matter of understanding our language better or our language games that philosophical puzzles arise because something has gone wrong in our language or maybe because philosophers have started misusing our language. G.E. Moore's common sense epistemology was a form of foundationalism, the proposition that beliefs are ultimately justified by

irrefutable foundational beliefs. Coherentism rejects this view entirely. A belief, say coherentists, can be called knowledge when it fits together with the rest of your beliefs. They believe that justification is not a linear process but rather a collection of criteria that come together to justify a system of beliefs. The American philosopher Willard van Orman Quine described this as the web of belief, a kind of seamless whole that is never immune from revision. In 1969, Quine wrote an article entitled Epistemology Naturalized, in which he put forth a radical new vision of epistemology. How did it transpire that the senses were bombarded by light waves and the like, and sound waves, and ultimately they, uh, these same people who were bombarded by light and by sound, issued forth in various sentences that formulated scientific theories, or if we can talk about beliefs, that they came to believe certain scientific theories about the beginning of the cosmos, the universe, or about what happened to the dinosaurs, and so on. How did that all happen? Well, that's a question for basically how the

mind works. Uh, how do beliefs form and theories form? So, that's a question for psychology. And Quine said in a very radical way, uh, well, so epistemology should be part of psychology. The totality of our so-called knowledge or beliefs, from the most casual matters of geography and history to the profoundest laws of atomic physics or even pure mathematics and logic, is a man-made fabric which impinges upon experience only along the edges. [Music] Another major challenge to traditional notions of epistemology came in the form of a brief but penetrating article written by the American philosopher Edmund Gettier. Gettier assaulted the idea of justified belief with the following scenario: suppose two people, Smith and Jones, went in for a job interview. They're sitting next to each other outside the boss's office, and as they're waiting, Smith watches as Jones counts the coins in her pocket. She has 10 coins. Jones goes into the interview, and just then the boss walks by and tells Smith that Jones is an old family friend, and

there's no way she's not getting the job. Smith is disappointed, to be sure, and he mumbles disconsolately to himself. The person who is getting the job has 10 coins in their pocket. But now suppose the boss was just kidding, and in fact, Smith was going to be offered the job instead. And suppose unbeknownst to Smith, he himself has 10 coins in his pocket. While it's clear that Smith's statement that the person who is getting the job has 10 coins in their pocket is in fact true, it's equally clear that Smith does not know that it is true. He had a justified true belief, but he didn't have knowledge. The unavoidable conclusion said Gettier was that knowledge must be something more than justified true belief. After Gettier, philosophers struggled to find a new condition of knowledge. Traditionally, epistemology had taken the internalist view that everything necessary to provide justification is available to consciousness. Descartes and Locke, worlds apart in many ways, were both internalists in that

for them, justification had to do with internal states of conscious awareness. Externalism, by contrast, involves factors external to the person. One of the externalist theories that arose after Gettier was the causal theory of knowledge. I propose the rather radical way to solve the problem, but not to solve the Gettier problem, but it was radical because of other differences in the approach that I put forward and what was popular at the time. So, I propose the causal theory of knowing, the idea, the rough idea being that if your belief in your mind is causally connected up in the appropriate way with the fact that makes what you believe true, then you know it. But if it's not connected up in the right way, then you don't know it. Suppose I'm driving through the countryside with my son and pointing out different things. I said, There is a cow, and there is a silo, there's a farmhouse, and there's a barn. And, um, you know, these are ordinary things. So, what I point out is a cow.

It is a horse and uh is a farmhouse and so on and is a barn okay but suppose that although the barn I point out is a regular old barn unbeknownst to me in that very neighborhood are lots and lots of other things which look like barns but are actually mirror facades say made of paper mache and if you went up close and walked around them you'd find they're not real barns at all but mere paper mache facades that from the road look exactly like a barn [Music] if what he saw really was an ordinary barn then when he said there's a barn he spoke the truth and not knowing there was anything odd about this District he was justified in his belief however in this District just looking out the window is not enough to know there is a barn out there in these particular circumstances looking out the window is an unreliable way of acquiring a belief about the barns that dot the countryside reliableism is the view that knowledge

is true belief that is justified in the circumstances. For example, Smith didn't know that the person with 10 coins in their pocket was going to get the job because his conclusion linking the coins to the job was not reliable in these circumstances. [Music] Reliableism is a form of externalism, the main form of externalism, which says that the reliability of a process or a method can contribute to its justification, conferring power, even if you don't know that it's reliable. Whereas other people say, Well, if you don't know that it's reliable, then it can't be relevant. Perhaps no other area of philosophy has inspired the creative imaginations of philosophers as much as the quest to understand knowledge. Somehow, this project brings out the storyteller in them, eliciting tales as varied as the sublime allegory of the cave to the serene tableau of barns dotting the countryside. And yet, epistemology must also contend with the powerful legacy of skepticism, with all the tales that have been told.

and theories put forth. We have to ask ourselves, what do we know about knowing now that wasn't known in ancient Greece? How dreadful knowledge of the truth can be, as Sophocles said, when there's no help in the truth.

A Brief History of Epistemology

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