Overview – The Definition of Knowledge

The definition of knowledge is one of the oldest questions of philosophy. Plato’s answer, that knowledge is justified true belief, stood for thousands of years – until a 1963 philosophy paper challenged this definition.

Edmund Gettier described two scenarios – now known as Gettier cases – where an individual has a justified true belief that is not knowledge.

Since Gettier’s challenge to the justified true belief definition, various alternative accounts of knowledge have been proposed. The goal of these accounts is to define ‘knowledge’ in a way that rules out Gettier cases whilst still capturing all instances of what we consider to be knowledge.

A Level philosophy looks at 5 definitions of knowledge:


Justified True Belief


It’s important to first distinguish the kind of knowledge we’re discussing in A level philosophy. Broadly, there are three kinds of knowledge:

  • Ability: knowledge howe.g. “I know how to ride a bike”
  • Acquaintance: knowledge of – e.g. “I know Fred well”
  • Propositional: knowledge that – e.g. “I know that London is the capital of England”

When we talk about the definition of knowledge, we are talking about the definition of propositional knowledge specifically.

The tripartite definition

In Theaetetus, Plato argues that for something to be knowledge it must be:

  • Justified
  • True
  • Belief

This is known as the tripartite definition of knowledge.

Necessary and sufficient conditions

Each of the three conditions above are necessary for knowledge.

For example, you can’t know something if it isn’t true. If someone said, “I know that the moon is made of green cheese” you wouldn’t consider that knowledge because it isn’t true.

Similarly, you can’t know something you don’t believe.

And finally, justification. Suppose you flip a coin and beforehand your friend says “I know it’s going to land on heads”.

How can they know this? Whether the coin lands on heads or tails is random – there’s no way you can realistically know beforehand which side it will land on. This doesn’t count as knowledge because it is not properly justified – even if he does get it right, it’s just a lucky guess, not knowledge.

Together, these necessary conditions (justified, true, and belief) are said to be jointly sufficient. This means they capture every instance of knowledge whilst not capturing anything that isn’t knowledge. This latter part is what Gettier cases challenge.

Problem: Gettier cases

Gettier’s paper describes two scenarios where an individual has a justified true belief that is not knowledge. One of Gettier’s scenarios is:

  • Smith and Jones are interviewing for the same job
  • Smith hears the interviewer say “I’m going to give Jones the job”
  • Smith also sees Jones count 10 coins from his pocket
  • Smith thus forms the belief that “the man who will get the job has 10 coins in his pocket”
  • But Smith gets the job, not Jones
  • And, by coincidence, Smith also has 10 coins in his pocket

Smith’s belief “the man who will get the job has 10 coins in his pocket” is:

  • Justified: he hears the interviewer say Jones will get the job and he sees that Jones has 10 coins in his pocket
  • True: the man who gets the job (Smith) does indeed have 10 coins in his pocket

But despite being a justified true belief, we do not want to say that Smith’s belief counts as knowledge because it’s just luck that led to him being correct.

This shows that the tripartite definition of knowledge is not sufficient.


Alternative definitions of knowledge


Gettier cases are a devastating problem for the tripartite definition of knowledge.

In response, philosophers have tried to come up with new definitions of knowledge that avoid Gettier cases.

Generally, these new definitions seek to refine the justification condition of the tripartite definition. True and belief remain unchanged.

JTB + no false lemmas

The no false lemmas definition of knowledge aims to strengthen the justification condition of the tripartite definition.

It says that James has knowledge of P if:

  • P is true
  • James believes that P
  • James’s belief is justified
  • James did not infer that P from anything false

So, basically, it adds an extra condition to the tripartite definition. It says knowledge is justified true belief + that is not inferred from anything false (a false lemma).

This avoids the problems of Gettier cases because Smith’s belief “the man who will get the job has 10 coins in his pocket” is inferred from the false lemma “Jones will get the job”.

Remember:

  • The tripartite definition says Smith’s belief is knowledge, even though it isn’t
  • The no false lemmas response says Smith’s belief is not knowledge, which is correct.

So, in this instance, the no false lemmas definition appears to be a more accurate account of knowledge than the tripartite view. It avoids saying Gettier cases count as knowledge.

Problem: fake barn county

However, the no false lemmas definition of knowledge faces a similar problem: the fake barn county situation:

Justified True Belief and Knowledge Venn Diagram
Venn diagram highlighting the problems with the JTB and JTB+N definitions. JTB+N is an improvement on JTB, but the fake barn county example shows that this definition still includes cases that are not knowledge.
  • In ‘fake barn county’, the locals create fake barns that look identical to real barns
  • Henry is driving through fake barn county, but he doesn’t know the locals do this
  • Henry often thinks “there’s a barn” when he looks at the fake barns
    • These beliefs are not knowledge, because they are not true – the barns are fake
  • However, on one occasion Henry looks at the one real barn and thinks “there’s a barn”
    • This time the belief is true
    • It’s also justified by his visual perception of the barn
    • And it’s not inferred from anything false.

According to the no false lemmas definition, Henry’s belief is knowledge.

But this shows that the no false lemmas definition must be false. Henry’s belief is clearly not knowledge – he’s just lucky in this instance.

Reliabilism

Simple reliabilism says James knows that P if:

  • P is true
  • James believes that P
  • James’s belief that P is caused by a reliable method

But this doesn’t solve the fake barn county example above. Henry’s belief that “there’s a barn” is caused by a reliable cognitive process – his visual perception. Even though it has let him down in this particular case, it’s normally a reliable method of forming true beliefs.

Robert Nozick: truth tracking

Nozick develops his own version of reliabilism, which aims to tie the method of justification to the truth.

Nozick says James knows that P if:

  • P is true
  • James believes that P
  • In the situation James is in, or a similar situation, if P were false, then James would not believe that P
  • In the situation James is in, or a similar situation, if P were true, then James would believe that P

Returning to fake barn county, this definition would correctly say Henry does not know what he’s looking at is a barn. This is because if it wasn’t a barn, Henry would still believe it was in this situation.

Problem: denying closure

Nozick’s truth tracking definition of knowledge avoids Gettier cases and the fake barn county scenario. However, it denies the epistemic closure principle – an outcome many philosophers find undesirable.

The epistemic closure principle allows you to make the inference from steps 1 and 2 below to step 3:

  1. James knows that P
  2. James knows that if P is true, then Q is also true
  3. Therefore, James knows that Q

The reason Nozick must deny closure is as follows:

  • According to Nozick’s definition of knowledge, I can say “I know I have hands” because if I didn’t have hands (in a similar situation) then I wouldn’t believe I have hands
  • But if I know I have hands, then I know I’m not a brain in a vat
  • Therefore, according to closure, I know I’m not a brain in a vat
  • However, according to Nozick’s definition, I can’t say “I know I’m not a brain in a vat” because if I was a brain in a vat, I wouldn’t believe I was a brain in a vat

To put it another way, Nozick’s definition of knowledge says that:

  1. You can know you have hands
  2. But not know you’re not a brain in a vat

Even though closure would suggest knowing 1 implies you’re not a brain in a vat.

Denying the validity of closure is seen as an undesirable outcome because it means a lot of inferences we make in everyday life are technically not valid (even though they obviously are). For example:

  1. I know it is Monday
  2. I know that if it is Monday, then I have philosophy class today
  3. Therefore, I know I have philosophy class today

But, according to Nozick, 3 does not logically follow from 1 and 2.

Infallibilism

Infallibilism argues that for a belief to count as knowledge, it must be true and justified in such a way as to make it certain.

So, even though Smith has good reasons for his beliefs in the Gettier case, they’re not good enough to provide certainty. Certainty, to philosophers like Descartes, means the impossibility of doubt.

In the Gettier case, Smith might have misheard the interviewer say he was going to give Jones the job. Or, even more extreme, Smith might be a brain in a vat and Jones may not even exist! Either of these scenarios – however unlikely – raise the possibility of doubt.

Problem: too strict

So, infallibilism correctly says Smith’s belief in the Gettier case does not count as knowledge.

But it also says pretty much everything fails to qualify as knowledge!

“I know that water boils at 100°c” – can this be doubted? Of course it can! Your science teachers might have been lying to you, you might have misread your thermometer, you might be a brain in a vat and there’s no such thing as water!

Pretty much any belief can be doubted.

So, whereas Gettier cases show the tripartite definition to set the bar too low for knowledge, infallibilism sets the bar way too high – barely anything can be known!

Virtue epistemology

Virtue epistemology says James knows that P only if:

  • P is true
  • James believes that P
  • James’s belief is a result of exercising his intellectual virtues

Intellectual virtues are intellectual faculties, such as good memory, accurate vision, the ability to think rationally, and so on.

You can think of intellectual virtues as traits that lead you to form true beliefs. The more advanced these traits, the more true beliefs you’ll form.

Returning to the fake barn county example, the intellectual virtue required here is the ability to tell real barns from fake barns. Since Henry lacks this ability, his belief cannot be the result of exercising his intellectual virtues. So, according to virtue epistemology, Henry’s belief would not count as knowledge as it’s formed as a result of luck, not intellectual virtue.


The Nature of Knowledge>>>