The Matryoshka Metaphor
What is Knowledge?

People use the word "know" all the time, but what does it mean? Most of us feel that we have an intuitive grasp of the concept, but providing a more rigorous analysis of it is difficult.

Types of Knowledge

Philosophers typically divide knowledge into three types: personal knowledge, procedural knowledge, and propositional knowledge. The primary concern of epistemology is propositional knowledge, but contrasting this with other types of knowledge can help in clarifying precisely what it is that epistemologists are discussing.

Theories of Knowledge

The most popular account of knowledge is the tripartite theory. This theory, which analyses knowledge as justified true belief, is widely used as a working model, even though most philosophers recognise that it has serious difficulties.

The closest thing to a rival to the tripartite theory is infallibilism, which suggests that knowledge requires absolute certainty, as opposed to belief or opinion about which there is more doubt.

Personal Knowledge

The first type of knowledge is personal knowledge, or knowledge by acquaintance.

Knowledge in this sense is to do with being familiar with something. In order to know Amy, one must have met her. In order to know fear, one must have experienced it.

In each of these cases, the word "know" is being use to refer to knowledge by acquaintance.

Personal knowledge does, arguably, involve possessing at least some propositional knowledge. If I have met Amy, but can't remember a single thing about her, then I probably wouldn't claim to know her. In fact, knowing a person (in the sense required for knowledge by acquaintance) does seem to involve knowing a significant number of propositions about them.

What is important is that personal knowledge involves more than knowledge of propositions. No matter how much you tell me about Amy, no matter how many facts about her I learn, if I haven't met her then I can't be said to know her in the sense required for personal knowledge.

Personal knowledge thus seems to involve coming to know a certain number of propositions in a particular way.

Procedural Knowledge

The second kind of knowledge is procedural knowledge, or knowledge how to do something. The claims to know how to juggle and how to drive are claims to have procedural knowledge.

Procedural knowledge clearly differs from propositional knowledge. It is possible to know all of the theory behind driving a car (i.e. to have all of the relevant propositional knowledge) without actually knowing how to drive a car (i.e. without having the procedural knowledge).

You may know which pedal is the accelerator and which is the break. You may know where the handbrake is and what it does. You may know where your blind spots are are when you need to check them. But until you get behind the wheel and learn how to apply all this theory, you do not know how to drive.

Knowing how to drive involves possessing a skill, being able to do something; that is very different to knowing a load of facts.

Propositional Knowledge

Although there are several different types of knowledge, the primary concern of epistemology is propositional knowledge. This is knowledge of facts, knowledge that such and such is the case.

The difference between the three types of knowledge is not as sharp as it might at first appear.

Personal knowledge does seem to involve knowledge of at least some propositions. Simply having met someone is not enough to know them (in the personal knowledge sense); you also have to know a few things about them (in the propositional knowledge sense).

Procedural knowledge also seems to involve some propositional knowledge. If you know how to drive a car (in the procedural knowledge sense) then you presumably know certain facts about driving (e.g. which way the car will go if you turn the steering wheel to the left).

What is important is that propositional knowledge is not enough to give you either personal knowledge or procedural knowledge. Personal knowledge involves acquiring propositional knowledge in a certain way, and procedural knowledge may entail propositional knowledge, but the same propositional knowledge certainly does not entail procedural knowledge.

Whatever the connections between the various types of knowledge may be, however, it is propositional knowledge that is in view in most epistemology.

The Tripartite Theory of Knowledge

There is a tradition that goes back as far as Plato that says that three conditions must be satisfied in order for one to possess knowledge. This account, known as the tripartite theory of knowledge, analyses knowledge as justified true belief. If you believe something, with justification, and it is true, the tripartite theory says, then you know it; otherwise, you do not.


The first condition for knowledge, according to the tripartite theory, is belief. Unless one believes a thing, one cannot know it. Even if something is true, and one has excellent reasons for believing that it is true, one cannot know it without believing it. Knowledge, quite clearly, requires belief.


The second condition for knowledge, according to the tripartite theory, is truth. If one knows a thing then it must be true. No matter how well justified or sincere a belief, if it is not true that it cannot constitute knowledge. If a long-held belief is discovered to be false, then one must concede that what was thought to be known was in fact not known. What is false cannot be known; knowledge must be knowledge of the truth.


The third condition for knowledge is justification. In order to know a thing, it is not enough to merely believe it; one must also have a good reason for doing so. Lucky guesses cannot constitute knowledge; we can only know what we have good reason to believe.

The tripartite theory of knowledge is intuitively very plausible. Since Edmund Gettier’s critique of it in the 60s, however, using thought-experiments now known as Gettier cases, it has been generally rejected. Nevertheless, it is still used as a working model by philosophers most of the time.

Gettier Cases

The tripartite theory of knowledge analyses knowledge as justified true belief. According to this analysis, if something is true, and we believe it to be true, and we are justified in believing it to be true, then we know it.

The tripartite theory, though it has been around since Plato, and though it is still widely used by many philosophers as a working model of knowledge, is false. This was shown to the satisfaction of most philosophers by Edmond Gettier, who developed what are now known as Gettier cases.

Gettier cases are cases in which the tripartite theory’s three conditions for knowledge are satisfied, i.e. in which a person does have a justified true belief, but in which there is no knowledge. The existence of such cases shows that there is something more to knowledge than justified true belief, and so that the tripartite theory of knowledge is false.

Suppose that two students, Mark and Sam, have taken a test. Mark is a straight A student, while Sam consistently fails any work he is set. Mark has attended the lessons in preparation for the test, while Sam has been absent due to illness. Mark revised hard for the test, while Sam stayed out all night at a party. Mark wrote furiously for the full duration of the test, while Sam wrote a few lines and then walked out in disgust. Mark says that the test went well, while Sam says that he didn’t even understand the question.

Reflecting on the test, and on a book that he has recently been reading, Sam forms the following belief: the student that will get the highest grade on the test shares a name with the author of The Adventures of Huckleberry Finn." Sam clearly has excellent evidence for this belief, he is justified in believing it; he has excellent evidence that Mark will get the highest grade on the test, and can see from the cover of his copy of "The Adventures of Huckleberry Finn that it was written by Mark Twain. Furthermore, the belief is true; the student that will get the highest grade on the test does indeed share a name with the author of "The Adventures of Huckleberry Finn." According to the tripartite theory of knowledge, therefore, Sam knows that the student that will get the highest grade on the test shares a name with the author of "The Adventures of Huckleberry Finn."

Sam, however, does not know this. Mark, despite his excellent grades in the past, perfect attendance, hours of revision, furious writing, and confidence, failed the test. He did not appreciate the subtlety of the question, and so missed its point entirely. Sam, on the other hand, despite his previous poor grades, frequent absences, late night partying, and pessimism concerning his performance, did understand the question. In the few lines that he wrote he managed to scrape a passing grade. Sam, therefore, rather than Mark, got the highest grade on the test.

Unknown to Sam, though, he does share a name with the author of The Adventure of Huckleberry Finn." Its author, who used the pseudonym Mark Twain, was in fact called Samuel Clemens. Sam, therefore, the student who will get the highest grade on the test, does share a name with the author of Huckleberry Finn."

Although Sam clearly did have a justified true belief, he equally clearly did not have knowledge. His justification for his belief, far from helping him to discern the truth, threatened to lead him astray. The truth of his belief had nothing to with his reasons for holding it; it was nothing more than good luck that the belief that he formed was true.

This example, and other Gettier cases like it, show that it is possible to have justified true belief without having knowledge; the tripartite theory of knowledge, which holds that justified true belief and knowledge are precisely the same thing, is therefore false.

Knowledge Without Belief?

According to the tripartite theory of knowledge, knowledge is justified true belief. One proposed counter-example to this theory is the case of the nervous student. This is supposedly a case of knowledge without belief, thus showing that it is possible to have knowledge without satisfying all three of the tripartite theory’s conditions for knowledge, that those conditions are not necessary.

The case of the nervous student is as follows: A student in a history class has been taught that the Battle of Hastings took place in 1066. The student, however, lacks confidence, and so when asked in a subsequent class when the Battle of Hastings occurred is convinced that he does not know. The date “1066” comes into his mind, but he does not give it any particular weight. However, absent any alternative ideas, this is the date that he gives in response to the question.

It seems that the student does know that the Battle of Hastings took place in 1066. He gave the correct answer to the question as to when it occurred, and he did so because he had been taught the correct date.

However, it also seems that the student does not believe that it occurred in 1066. If he were asked whether he believes that it occurred in 1066, he would dissent, and he of all people knows best what he believes and what he does not.

The nervous student thus appears to have knowledge without belief. The conditions for knowledge proposed by the tripartite theory therefore do not seem to be necessary; it seems to be possible to have knowledge without satisfying all three conditions.

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