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What is Knowledge?

Grunge Knowledge

The Knowledge Problem

Studying knowledge is something philosophers have been doing for as long as philosophy has been around. It’s one of those perennial topics—like the nature of matter in the hard sciences--that philosophy has been refining since before the time of Plato. The discipline is known as epistemology which comes from two Greek words episteme (episthmh) which means knowledge and logos (logoV) which means a word or reason. Epistemology literally means to reason about knowledge. Epistemologists study what makes up knowledge, what kinds of things can we know, what are the limits to what we can know, and even if it’s possible to actually know anything at all.

At first this might seem like one of those topics that gives philosophy a bad name. After all, it seems kind of silly to ask whether we can know anything since is obvious we do. It's even more silly when you consider that to even ask the question, you must assume you know something! So why have some of the greatest minds the world has ever produced spent such a great deal of time on the subject? In this article I’ll consider this question.

Do We Know Stuff?

In order to answer that question, you probably have to have some idea what the term “know” means. If I asked, “Have you seen the flibbertijibbet at the fair today?” I’d guess  you wouldn’t know how to answer. You’d probably ask me what a flibbertijibbet is. But most adults tend not to ask what knowledge is before they can evaluate whether they have it or not. We just claim to know stuff and most of us, I suspect, are pretty comfortable with that. There are lots of reasons for this but the most likely is that we have picked up a definition over time and have a general sense of what the term means. Many of us would probably say knowledge that something is true involves:

  1. Certainty – it's hard if not impossible to deny
  2. Evidence – it has to based on something
  3. Practicality – it has to actually work in the real world
  4. Broad agreement – lots of people have to agree it's true

But if you think about it, each of these has problems. For example, what would you claim to know that you would also say you are certain of? Let’s suppose you’re not intoxicated, high, or in some other way in your “right” mind and conclude that you know there is a computer in front of you. You might go further and claim that denying it would be crazy. Isn’t it at least possible that you’re dreaming or that you’re in something like the Matrix and everything you see is an illusion? Before you say such a thing is absurd and only those who were unable to make the varsity football team would even consider such questions, can you be sure you’re not being tricked? After all, if you are in the Matrix, the robots that created the Matrix would making be making you believe you are not in the Matrix and that you’re certain you aren’t.

What about the “broad agreement” criterion? The problem with this one is that many things we might claim to know are not, and could not be, broadly agreed upon. Suppose you are experiencing a pain in your arm. The pain is very strong and intense. You might tell your doctor that you know you’re in pain. Unfortunately though, only you can claim to know that (and as an added problem, you don’t appear to have any evidence for it either—you just feel the pain). So at least on the surface, it seems you know things that don’t have broad agreement by others.

These problems and many others are what intrigue philosophers and are what make coming up with a definition of knowledge challenging. Since it’s hard to nail down a definition, it also makes it hard to answer the question that heads this section.

So, What is Knowledge?

Okay, a definition is tough to come by. But philosophers have been attempting to construct one for centuries. Over the years, a trend has developed in the philosophical literature and a definition has emerged that has such wide agreement it has come to be known as the “standard definition.” As with most things in philosophy, the definition is controversial and there are plenty who disagree with it. But as these things go, it serves as at least the starting point for studying knowledge.

The definition involves three conditions and philosophers say that when a person meets these three conditions, she can say she knows something to be true. Take a statement of fact: The Seattle Mariners have never won a world series.  On the standard definition, a person knows this fact if:

  1. The person believes the statement to be true cognitum text
  2. The statement is in fact true
  3. The person is justified in believing the statement to be true

The bolded terms earmark the three conditions that must be met and because of those terms, the definition is also called the “tripartite” (three part) definition or “JTB” for short. Many many books have been written on each of the three terms so I can only briefly summarize here what is going on in each. (I will say up front though that epistemologists spend most of their time on the third condition.)


First, beliefs are things people have. Beliefs aren’t like rocks or rowboats where you come across them while strolling along the beach. They’re in your head and generally are viewed as just the way you hold the world (or some aspect of the world) to be. If you believe that the Mariners never won a world series, you just think that the Mariners really never won a world series. If you read that last sentence carefully, you’ll notice I wrote “you just think.” For many philosophers, this is important. It implies that what you think could be wrong. In other words, it implies that what you think about the world may not match up with the way the world really is and so there is a distinction between belief and the next item in our list, truth. There are some philosophers--notably postmodernists and existentialists--who think such a distinction can’t be made. See the section below on Postmodernism for an overview of this idea. Some philosophers argue that a good test for showing what you really believe is to look at how you behave. People will generally act, they argue, according to what they really believe rather than what they say they believe—despite what Dylan says.


Something is true if the world really is that way. Truth is not in your head but is “out there.” The statement, “The Mariners have never won a world series” is true if the Mariners have never won a world series. No, I didn’t just repeat myself. The first part of that sentence is in quotes on purpose. The phrase in quotes signifies a statement we might make about the world and the second, unquoted phrase is supposed to describe the way the world actually is. The reason philosophers write truth statements this way is to give sense to the idea that a statement about the world could be wrong or, more accurately, false (philosophers refer to the part in quotes as a statement or proposition). Perhaps you can now see why beliefs are different than truth statements. When you believe something, you hold that or accept that a statement or proposition is true. It could be false that’s why your belief may not “match up” with the way the world really is.


If the seed of knowledge is belief, what turns belief into knowledge? This is where justification comes in (some philosophers use the term “warrant” to refer to this element). A person knows something if they’re justified in believing it to be true (and, of course, it actually is true). There are dozens of competing theories of justification and there is little consensus about which is the right one. It’s sometimes easier to describe when a belief isn’t justified than when it is. In general, philosophers agree that a person isn’t justified if their belief is:

  1. a product of wishful thinking (e.g. I really wish you would love me so I believe you love me)
  2. a product of fear or guilt (e.g. you’re terrified of death and so form the belief in an afterlife)
  3. a product of guesswork
  4. formed in the wrong way (e.g. you travel to an area you know nothing about, see a white spot 500 yards away and conclude it’s a sheep)
  5. a product of dumb luck (e.g. you randomly form the belief that the next person you meet will have hazel eyes and it turns out that the next person you meet has hazel eyes)

Justification is hard to pin down because beliefs come in all shapes and sizes and it’s hard to find a single theory that can account for everything we would want to claim to know. You might be justified in believing that the sun is roughly 93 million miles from the earth much differently than you would be justified in believing God exists or that you have a minor back pain. Even so, justification is a critical element in any theory of knowledge and is the focus of many a philosophical thought.

Edmund-Gettier (photo from[Incidentally: while JTB is generally considered a starting point for a definition, it by no means is the final word. Many philosophers reject the JTB formulation altogether and others think that, at the very least, JTB needs to be “fixed up” somehow. Regarding this latter category, a small paper written by a philosopher named Edmund Gettier really kicked off a brouhaha that made philosophers doubt that JTB was sufficient for knowledge. Gettier’s paper was roughly two and a half pages long (almost unheard of in philosophy) but has become so important that the issues he raised are known as The Gettier Problem. I’m writing a series for Philosophy News in which I attempt to tackle some of Gettier’s challenges. You can read those articles here (these are not for the general reader but if you skim the first couple of articles, they may help frame some broader issues in epistemology).]

People at the Center

You might notice that the description above puts the focus of knowing on the individual. Philosophers talk of individual persons being justified and not the ideas or concepts themselves being justified. This means that what may count as knowledge for you may not count as knowledge for me. Suppose you study economics and you learn principles in the field to some depth. Based on what you learn, you come to believe that psychological attitudes have just as much of a role to play in economic flourishing or deprivation as the political environment that creates economic policy. Suppose also that I have not studied economics all that much but I do know that I’d like more money in my pocket. You and I may have very different beliefs about economics and our beliefs might be justified in very different ways. What you know may not be something I know even though we have the same evidence and arguments in front of us.

So the subjective nature of knowledge partly is based on the idea that beliefs are things that individuals have and those beliefs are justified or not justified. When you think about it, that makes sense. You may have more evidence or different experiences than I have and so you may believe things I don’t or may have evidence for something that I don’t have. The bottom line is that “universal knowledge” – something everybody knows—may be very hard to come by. Truth, if it exists, isn’t like this. Truth is universal. It’s our access to it that may differ widely.

Rene Descartes and the Search for Universal Knowledge

A lot of people are uncomfortable with the idea that there isn’t universal knowledge. Philosopher Rene Descartes (pronounced day-cart) was one of them. When he was a young man, he was taught a bunch of stuff by his parents, teachers, priests and other authorities. As he came of age, he, like many of us, started to discover that much of what he was taught either was false or was highly questionable. At the very least, he found he couldn’t have the certainty that many of his educators had. While many of us get that, deal with it, and move on, Descartes was deeply troubled by this.

One day, he decided to tackle the problem. He hid himself away in a cabin and decided to get to the bottom of it. He resolved to doubt everything of which he could not be certain. Since it wasn’t practical to doubt every belief he had, Descartes decided that it would be sufficient to subject the foundations of his belief system to doubt and the rest of the structure will "crumble of its own accord." He first considers the things he came to believe by way of the five senses. For most of us these are pretty stable items but Descartes found that it was rather easy to doubt their truth. The biggest problem is that sometimes the senses can be deceptive. And after all, could he be certain he wasn’t insane or dreaming when he saw that book or tasted that honey? So while they might be fairly reliable, the senses don’t provide us with certainty—which is what Descartes was after.

Rene DescartesNext he looked at mathematics. If certainly is to be found, it must be here. He reasoned that the outcome of mathematical formulas and theorems hold both in dreams and in waking so at the very least, it fares better than the senses. But he developed an argument from which he could not spare math. Suppose there is an evil genius, he thought, that is “supremely powerful and clever” and was bent upon deceiving Descartes and developed mathematics as a device to carry out his evil deceptions (the popular movie, The Matrix should be coming to mind about now). Descartes found there was no way to rule this possibility out. Whether it’s highly unlikely or not isn’t the point. Descartes was looking for certainty and if there is even a slim possibility that he’s being deceived, he had to throw out mathematics too.

Unfortunately, this left Descartes with no where to turn. He found that he could be skeptical about everything and was unable to find a certain foundation for knowledge. But then he hit upon something that changed modern epistemology. He discovered that there was one thing he couldn’t doubt: the fact that he was a thinking thing. In order to doubt it, he would have to think (he reasoned that it’s not possible to doubt something without thinking about the fact that you’re doubting). If he was thinking then he must be a thinking thing and so he found that it was impossible to doubt that he was a thinking being.

This seemingly small but significant truth led to his most famous contribution to Western thought: cogito ergo sum (I think, therefore I am). Some mistakenly think that Descartes was implying with this idea that he thinks himself into existence. But that wasn’t his point at all. He was making a claim about knowledge. Really what Descartes was saying is: I think, therefore I know that I am.

The story doesn’t end here for Descartes but for the rest of it, I refer you to the reading list below to dig deeper. The story of Descartes is meant to illustrate the depth of the problems of epistemology and how difficult and rare certainty is, if certainty is possible—there are plenty of philosophers who think either that Descartes’ project failed or that he created a whole new set of problems that are even more intractable than the one he set out to solve.

Postmodernism and Knowledge

The term "postmodern" has been applied to many things including art, music, and clothing. In this overview, I'm talking only about postmodern epistemology. Postmodern epistemology is difficult to pin down because, almost by definition, it is resistant to being defined. Generally, though, it means taking a specific, skeptical attitude towards certainty, and a relative view of belief and knowledge. Postmodernists see truth as much more fluid than classical (or modernist) epistemologists. Using the terms we learned above, they reject the idea that we can ever be fully justified in holding that our beliefs line up with the way the world actually is. We can't know that we know.

In order to have certainty, postmodernists claim, we would need to be able to "stand outside" our own beliefs and look at our beliefs and the world without any mental lenses or perspective. It's similar to wondering what it would be like to watch ourselves meeting someone for the first time? We can't do it. We can only meet someone for the first time as us so we have that experience only from "inside" our minds and bodies. Since its not possible to stand outside our minds, all the parts that make up our minds influence our view on what is true. Our intellectual and social background, our biases, our moods, our genetics, other beliefs we have, our likes and dislikes, our passions (we can put all these under the label of our "cognitive structure") all influence how we perceive what is true about the world. Further, say the postmodernists, it's not possible to set aside these influences or lenses. We can reduce the intensity here and there and come to recognize biases and adjust for them for sure. But it's not possible to completely shed all our lenses which color our view of things and so it's not possible to be certain that we're getting at some truth "out there."

And now we can see why postmodernists tend to eschew definition. Notice that as soon as a postmodernist makes a claim about the truth and knowledge they seem to be making a truth statement! If all beliefs are seen through a lens, how do we know the postmodernists beliefs are "correct?" That's a good question and the postmodernist might respond by saying, "We don't!" But then, why believe it? Because of this obvious problem, many postmodernists attempt to simply live with postmodernist "attitudes" towards epistemology and avoid making too many truth claims.

To be sure, Postmodernists do tend to act like the rest of us when it comes to interacting with the world. They drive cars, fly in airplanes, make computer programs, and even write books! But how is this possible if they take such a fluid view of truth? Postmodernists don't eschew truth in general. They reject the idea that any one person's beliefs about it can be certain. Rather, they claim that truth emerges through community agreement. Suppose scientists are attempting to determine whether the planet is warming and that humans are the cause. This is a complex question and a postmodernist might say that if the majority of scientists agree that the earth is warming and that humans are the cause, then that's true. Notice that the criteria for "truth" is that scientists agree. To use the taxonomy above, this would be the "justification condition." So we might say that postmodernists accept the first and third conditions of the tripartite view but reject the second condition: the idea that there is a truth that is "out there." Rather, truth is a product of people in a given community meeting the third condition and it is not something separate from that.

When you think about it, a lot of what we would call "facts" are determined in just this way. For many years, scientists believed in a substance called "phlogiston." Phlogiston was stuff that existed in certain substances (like wood and metal) and when those substances were burned, more phlogiston was added to the substance. Phlogiston was believed to have negative weight, that's why things got lighter when they burned. That theory has since been rejected and replace by more sophisticated views involving oxygen and oxidation.

So, was the phlogiston theory true? The modernist would claim it wasn't because it has since been shown to be false. It's false now and was false then even though scientists believed it was true. Beliefs about phlogiston didn't line up with the way the world really is, so it was false. But the postmodernist might say that phlogiston theory was true for the scientists that believed it. We now have other theories that are true. But phlogiston theory was no less true then than oxygen theory is now. Further, they might add, how do we know that oxygen theory is really the truth? Oxygen theory might be supplanted some day as well but that doesn't make it any less true today.

So postmodernism generally adheres to the following:

  1. Everyone comes to belief with a cognitive structure that cannot be set aside.
  2. Our cognitive structure serves as a lens through which we view the world. Because of this, knowledge is said to be perspectival or a product of our perspective.
  3. Since the evaluation of our beliefs is based on our cognitive lens, it's not possible to be certain about any belief we have. This should make us tentative about truth claims and more open to the idea that all of our beliefs could be wrong.
  4. Truth emerges in the context (or relative to) community agreement.

So What, Who Cares?

Well most of us aren’t like Descartes. We actually have lives and don’t want to spend time trying to figure out if we’re the cruel joke of some clandestine mad scientist. We can get by just fine, thank you, without having to think about all this stuff. But we actually do actually care about this topic whether we “know” it or not. A bit of reflection exposes just how important having a solid view of knowledge actually is and spending some focused time thinking more deeply about knowledge can actually help us get better at knowing.

Really, knowledge is a the root of many (dare I say most) challenges we face in a given day. Once you get past basic survival (though even things as basic as finding enough food and shelter involves challenges related to knowledge), we’re confronted with knowledge issues on almost every front. Knowledge questions range from larger, more weighty questions like figuring out who our real friends are, what to do with our career, or how to spend our time, what politician to vote for, how to spend or invest our money, should we be religious or not, to more mundane ones like which gear to buy for our hobby, how to solve a dispute between the kids, where to go for dinner, or which book to read in your free time. We make knowledge decisions all day, every day and some of those decisions deeply impact our lives and the lives of those around us.

So all these decisions we make about factors that effect the way we and others live are grounded in our view of knowledge—our epistemology. Unfortunately few spend enough time thinking about the root of their decisions and many make knowledge choices based on how they were raised (my mom always voted Republican so I will), what’s easiest (if I don’t believe in God, I’ll be shunned by my friends and family), or just good, old fashioned laziness. But of all the things to spend time on, it seems thinking about how we come to know things should be at the top of the list given the central role it plays in just about everything we do.

In Sum

I’ve only been able to scratch the surface on this massive but immensely interesting discipline. Much of what I’ve written in this article just sets up the classical investigation into what knowledge is. I recommend that you pick up one or more of the books in the list below to dig deeper. Who knows, maybe you’ll come to know that what you thought you knew you didn’t really know and, perhaps, come to know some new things.

Updated March, 2014:

  • Removed reference to dated events
  • Removed section on thought experiment
  • Added section on Postmodernism
  • Made minor formatting changes

For Further Reading

Bonjour Epistemology

Epistemology: Classic Problems and Contemporary Responses (Elements of Philosophy)
Laurence BonJour 
One of the better introductions to the theory of knowledge. Written at the college level, this book should be accessible for most readers but have a good philosophical dictionary on hand.


Belief, Justification, and Knowledge: An Introduction to Epistemology (Wadsworth Basic Issues in Philosophy Series)
Robert Audi
This book has been used as a text book in college courses on epistemology so may be a bit out of range for the general reader. However, it gives a good overview of many of the issues in the theory of knowledge and is a fine primer for anyone interested in the subject.

Pojman Theory of Knowledge

The Theory of Knowledge: Classic and Contemporary Readings
Louis Pojman 
Still one of the best books for primary source material. The edited articles have helpful introductions and Pojman covers a range of sources so the reader will get a good overview from many sides of the question. Written mainly as a textbook.

Pinker Stuff of Thought

The Stuff of Thought: Language as a Window into Human Nature
Steven Pinker
While not strictly a book about knowledge per se, Pinker’s book is fun, accessible, and a good resource for getting an overview of some contemporary work being done mainly in the hard sciences.

Descartes Principles

The Selections From the Principles of Philosophy
René Descartes
A good place to start to hear from Descartes himself.

Descartes Bones

Descartes' Bones: A Skeletal History of the Conflict between Faith and Reason
Russell Shorto
I’ve recommended Shorto’s book in other articles. This book is written as a history so it's not strictly a philosophy tome. However, it gives the general reader some insight into what Descartes and his contemporaries were dealing with and is a fun read.

Frankfurt on Knowledge

On Bullshit
Harry Frankfurt
One get’s the sense that Frankfurt was being a bit tongue-in-cheek with the small, engaging tract. It’s more of a commentary on the social aspect of epistemology and worth reading for that reason alone. Makes a great gift!

Frankfurt on Truth

On Truth
Harry Frankfurt 
Like On Bullshit but on truth.

Weston on Arguments

A Rulebook for Arguments
Anthony Weston
A handy reference for constructing logical arguments. This is a fine little book to have on your shelf regardless of what you do for a living.

Duncan Knowledge

The Proof of the External World: Cartesian Theism and the Possibility of Knowledge
Steven M Duncan
Not for the general reader but a solid book on how Descartes epistemology could be applied. Even if you don’t find Duncan’s arguments compelling, his thought will challenge you and isolate some key problems in epistemology.

Plantinga Warrant

Warrant: The Current Debate
Alvin Plantinga
Now close to 20 years old, the “current” in the title is a bit inaccurate. Still, many of the issues Plantinga deals with are with us today and his narrative is sure to enlighten and prime the pump for further study.
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