What is knowledge?

What is knowledge?


AC Grayling on knowledge


The question of ‘what is knowledge’ is fundamental to TOK, but although you’ll see that oft-used definition ‘Justified true knowledge’, AC Grayling shows us that Plato’s words are far more meaningful when they are applied to the question ‘When is it the case that you know something?’ He tells us that three conditions need to be satisfied:
First, that what you know is true. The problem with this is that truth is a very subjective term, and what we think of as being true may not be the same as other perspectives.
Second, you need to believe in what you know. Again, there are problems here, as you can believe that something is true when in fact it is false.
Third, you have to have a justification for knowing something. Grayling argues that this is the key condition to understand, as justification is the connection between your belief, and the knowledge being true.

Bertrand Russell’s way of dividing up knowledge

Drawing on the work by other philosophers, Bertrand Russell argued that knowledge fell into two categories: either knowledge by acquaintance, or, knowledge by description.
Knowledge by acquaintance is knowledge based on personal experience. Examples of this sort of knowledge could be places we have visited, books we have read, and people we have met and spoken to. Knowledge by description, on the other hand, is knowledge that we have not acquired by direct experience. Examples include places that we have only seen photos of, books we have just read reviews of, and people we only know through other people.

Traditional epistemological way of viewing knowledge

In university courses devoted to epistemology (which is anything to do with the nature of knowledge, and how we obtain it), knowledge is often divided up into knowing that and knowing how knowledge. Knowing that is anything based on facts or opinions – anything that can be said to be either true or not true. This is also known as propositional knowledge, and is the type of knowledge that we are concerned with in TOK (and, indeed, epistemology).
Knowing how is skill-based knowledge, or things we know how to do, like playing a sport, programming a computer, painting a picture, and so on. This is not really the type of knowledge we are going to be looking at during this course.

The Empirical/Rational way of approaching knowledge

Imagine this hypothetical scenario (apologies for drawing on a hypothetical example!).
Whilst travelling in South America with a friend, you meet another backpacker in a bar, and swap stories. He tells you about the Darian Gap, the area of road-less territory on the border between Colombia and Panama. He tells you that he travelled across this border, and during the process was robbed on two occasions by bandits, losing most of his stuff. Then he found himself kidnapped by Colombian rebels, and marched towards a jungle camp where he was in danger of being imprisoned. Fortunately, he managed to escape, and make it to the road, from where he hitched a ride to safety. He tells you that it should on no account be attempted, because it is extremely unsafe.
You and your friend were planning to travel up into Central America via the Darian Gap, but on hearing this story, you have decided to change your route. Clearly, it is far too dangerous to be attempted, so it would be much more advisable to catch a plane. However, your friend doubts the story, and wants to experience the Darian Gap for himself. He doesn’t like to believe in something that he hasn’t experienced for himself, and for that reason refuses to change his plan.
For you, the story told by the backpacker, perhaps confirming stories that you have already heard about the region, makes you conclude that it would be too dangerous to travel there. Your friend, however, refuses to make any decision about your holiday destination until he has seen the situation for himself. He needs to experience things for himself, and see them through his own eyes.
In short, your friend and you have two different approaches to reasoning. You build up a picture of the world by using second hand knowledge that fits in with what you already know. This is known as rationalism. Your friend bases his knowledge only on the things that he witnesses and experiences first hand. This is known as empiricism.

The line between these two ‘schools of thought’ can sometimes be hazy, and obviously there are few people who can be described as either 100% rational or 100% empirical. Most of us use both ways to acquire and apply knowledge. But they are quite a useful way of dividing up knowledge, and both have a long philosophical history, which are worth exploring a little.


Rationalism, in its purest sense, is a belief that all knowledge comes to us through our intellect and our powers of reason. We cannot trust knowledge that comes to us through our senses, because our senses are unreliable. Rationalism can be traced back as far as the Greek philosophers, with its founding fathers arguably Socrates (who never wrote anything down) and his pupil Plato (who did).
Socrates and Plato believed that our senses only allow us to view the physical world, which to them was far less important than the internal world of thoughts, feeling, and emotions – in other words, our souls. It is only by knowing your soul that you can know yourself, but to this you have to go beyond conscious knowledge. We’ll come back to the work of Plato when we look at reason, and try to understand more about this with his famous metaphor of the cave.
The more modern figure who is associated with rationalism is the French philosopher Descartes. You probably already know Descartes’ most famous phrase: ‘I think, therefore I am.’ But you may not understand exactly what he meant. Descartes arrived at it by asking himself the question: ‘What can I be sure of?’ He concluded that he could doubt pretty much everything that he had ever been told, seen, heard, or learnt. As he put it:

I realized that it was necessary, once in the course of my life, to demolish everything completely and start again right from the foundations if I wanted to establish anything at all in the sciences that was stable and likely to last.

This meant, above all else, doubting the knowledge provided by the senses. Descartes then set about rebuilding a view of the world that was based on much surer foundations. He set out this process in his Meditations, which describes a number of ‘truths’.
Truth number one: The first thing we can be sure of is that we exist, because are able to ask ourselves that question. This is what gave rise to his famous adage, ‘I think, therefore I am’ – being able to think, and ask the question, proves that we exist.
Truth number two: But what was it that allowed him to know the first truth? Descartes said that he must have had a ‘clear and distinct perception of what I was asserting.’ In other words, for Descartes, whatever is clear and discernible is true.
Truth number three: God, being perfect, could not be imagined or discerned by any other source than a perfect one – or, God himself. Not only that, but this idea must have been implanted within us from the moment we start existing.
Truth number four: All trustworthy knowledge we have, such as truth, mathematical numbers, and geometrical forms, are innate, and given to us by God. This is in contrast to knowledge that is accessed via the senses (such as colour or scent), which is obscure and confused. He didn’t say that we should ignore sensory knowledge, but he believed we should analyse it in as scientific a way as possible, by breaking it down to its constituent parts, and using mathematics to approach it.
To illustrate the dangers of taking a non-scientific approach, he suggests that the reader of Meditations try to conceive of a chiliagon – a geometrical figure with 1000 sides. Logically and mathematically, this is possible to do – we can calculate the number of right angles within it, and distinguish it from a figure with 1001 sides. But to do so via the imagination is impossible. For Descartes, imagination was aligned to sense perception, and should therefore only be used for bodily survival. Knowledge via sense perception is not designed to show us the true nature of the universe. Instead, we should rely on reason to provide us with certain knowledge.


Empiricism, also, can be traced back to the Greeks. We owe a lot to them! It is based on the idea that people’s minds begin like a ‘blank slate’ – or tabula rasa – on which experience is written, to create a picture of the world and how it works. How full this picture is depends on how much experience we gain, and how much we see for ourselves. The person who first expressed the idea that the mind was a tabula rasa was Aristotle, who was actually Plato’s pupil.
Again, there is a more modern philosopher who is linked to this school of thought. His name is John Locke, and he is one of the most influential English philosophers who has ever lived. He came across the ideas of Descartes when he was still a student at Oxford. He then began to construct a theory of knowledge to rival Descartes’.
His Essay Concerning Human Understanding was written in order to ‘search out the bounds between opinion and knowledge.’ In many ways, this was very ahead of its time – he argued, for example, that people whose beliefs and faiths differed from the majority should not be attacked or criticised. Encouraging tolerance was one of his key agendas.
His problem with Descartes’ ideas began with the concept of innate ideas. The rationalists claimed that certain principles were adhered to by all human beings, but Locke disagreed with this. He could not accept that certain truths were ‘imprinted on the soul’, but not always recognised or understood (for example, by children). To access a truth ‘within us’ solely by the use of reason seemed a contradiction, and made no sense to Locke.
Instead, for Locke and his followers – who were known as empiricists – our minds are ‘blank sheets’, and our first ideas come to us via the senses. Knowledge about objects and people is gradually built up as we are exposed to them, and at the same time our mental powers develop allowing us to gain ‘ideas of reflection.’ We therefore have two mechanisms to learn about the world – sensation of external things, and mental reflection.
Locke’s definition of knowledge was ‘the perception of the connection and agreement, or disagreement and repugnancy, of any of our ideas.’ Testing ideas for agreement or disagreement could be done in a number of ways, which Locke called the ‘degrees’ of knowledge:
The most immediate way in which we gain knowledge is intuitive knowledge. This allows us to establish an agreement or disagreement immediately, which we might do if we are presented with a statement such as ‘a circle has no angles’, or ‘a triangle has four sides.’
More difficult is demonstrative knowledge, which requires the help of connecting ideas. We may require this if we are establishing that the angles of a triangle add up to two right angles.
Sensitive knowledge, Locke’s third type of knowledge, deals with experiences and sensations. Sensitive knowledge links our minds to reality, allowing us to be aware of the food we eat, how hot it is, the colour of the shoes we are wearing. This also involves us mentally reflecting, as we unconsciously test whether the feeling we are experiencing matches up to our idea of that feeling.
Whilst Descartes was deeply concerned with certainty, and whether or not we are being misled about the nature of reality, Locke spent little time in pondering this question. Instead, he believed we are ‘invincibly conscious’ of reality, and took a very pragmatic approach to reality: knowledge for him was a tool for the pursuit of happiness. However, he was wary of ‘judgement’, which he believed was distinct, and weaker, from ‘knowledge’.
As Jennifer Nagel points out, given that both men were writing at a similar time, and embraced the new scientific way of thinking, it is perhaps surprising that they arrived at very different theories of knowledge. She suggests that the reason for this is the emphasis Descartes placed on a ‘first-person’ approach to knowledge, asking the question, ‘What can I know for certain?’ This leads him to mistrust the knowledge provided by the senses, and focus on mathematical and abstract ideas. Locke, on the other hand, asks, ‘What do human beings know?’ This observational, third-person approach makes sense perception a more natural foundation for knowledge.
Both these ways of looking at the world help us to make knowledge claims. ‘Knowledge claims’ are statements or propositions that we believe to be true, and it is a phrase used a lot in Theory of Knowledge. But before we go any further, we need to think about a little word that is such an important part of our world: ‘truth’.

Cite this page as: Dunn, Michael. What is knowledge? (8th May 2013). theoryofknowledge.net. http://www.theoryofknowledge.net/knowledge-and-knowers/what-is-knowledge/ Last accessed: 22nd January 2017


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