Knowledge theory

What is truth and what is knowledge? These are questions philosophers have been busy discussing for thousands of years. Knowledge theory is sometimes called epistemology. It is about the nature of knowledge and deals with concepts like truth, knowledge, belief, and justification (of beliefs). This branch of philosophy aims to answer questions like “What do we know?”, “What does it mean that we know something?”, “What makes beliefs justified?”, and “How do we know that we know?”.

This project comes with bold claims that go beyond the current state of knowledge so it is important to evaluate them and the evidence. This succinct treatise on knowledge theory is an historical account as thoughts are usually built upon previous thoughts. It discusses Western philosophy even though many of the ideas presented here have been invented elsewhere too. The reason is that the scientific revolution took place in the Western world and science is based on thinking but also greatly has influenced thinking so this is easiest way to tackle the most relevant topics.

Classical philosophy

The first ancient Greek philosophers speculated about the nature of reality. This is called metaphysics. Some early Greek philosophers believed that reality consisted of four basic ingredients. These are fire, water, earth and air. Later on a few Greek philosophers argued that the building blocks of reality are small particles called atoms that differ in shape and size and that the objects we see are groups of atoms stuck together. This was already close to the modern understanding of reality.

There were other issues that the ancient Greeks were thinking about. Some of them figured that the Earth could be a sphere. They guessed it by looking at the sea. The sea horizon is slightly curbed while boats disappear in the distance before their sails do. A philosopher named Xenophanes began to doubt religion. He realised that people believed that the gods are like themselves. For instance, black people believed that the gods are black while red-haired people believed them to be red-haired. He then argued that we can’t know what the gods are like. This was an early form of scepticism.

And why would you believe in the Greek gods if the Persians and the Egyptians have different gods? If your place of birth determines what you believe then your beliefs probably are false. The sophists were an early group of philosophers who had come into contact with other cultures. They claimed that absolute knowledge is impossible. Everything is subjective, they argued. This is called relativism. Socrates is known for his dialogues in which he debated the sophists.

Socrates claimed that there is absolute truth even though we may not know it. His pupil Plato claimed that ideas are at the basis of knowledge. He believed that ideas are more real than things. This is called idealism. Plato’s pupil Aristotle on the other hand believed that knowledge comes from observations. This is called empiricism. Both approaches have their problems. If you imagine that unicorns exist, you have the idea of a unicorn. The idealist reasoning could be that therefore unicorns exist. On the other hand, if you see a unicorn after eating some mushrooms, the empiricist reasoning could be that unicorns exist for that reason.

The foundations of knowledge can always be called into question. It is for that reason that scepticism emerged. In ancient times there were two main groups of sceptics. The first group argued that nothing is certain. They aimed at refuting the claims of other philosophers. The second group claimed that it often isn’t possible to prove or refute claims and that it is better to postpone judgement until the matter is sufficiently clarified.

These ideas were revived in Europe during the late Middle Ages after the texts of the classical philosophers were rediscovered in Arab libraries. European philosophers of that time like Thomas Aquinas and William of Ockham were theologians who believed that there is no difference between theology and science. Over time science and religion became separated as they both come from different sources. Science is based on observations and reason while religion was believed to be based on divine revelation.

Ockham is known for his simplicity principle called Ockham’s razor. It means that simple explanations are more likely to be true than complex ones. It is usually phrased as follows: “If there are several hypotheses that can explain a phenomenon equally, the hypothesis that comes with the fewest entities should be selected.” Introducing additional unproven assumptions reduces the likelihood of the conclusion being true. This argues for minimalism in reasoning. If you want to prove a point it is better not to introduce unnecessary assumptions.

Modern philosophy

Around the year 1500 European thinkers began to realise that Christopher Columbus had just discovered a completely new continent. Traditional knowledge had failed dramatically here. At the same time Protestants began to challenge the authority of the Roman Catholic Church. The ensuing religious wars ravaged Europe. They ended without a clear winner. And so the question arose as to how to evaluate the claims of the different branches of Christianity. After all, they can’t all be true.

brain in a vat believing itself to be a person who is walking

These developments spurred a renewed scepticism and a new search for the foundations of knowledge. As our senses can be deceptive, only rational thinking can produce knowledge, philosophers like René Descartes, Gottfried Leibniz and Baruch Spinoza argued. Their view is called rationalism, but it was a new version of idealism. In a thought experiment similar to the brain-in-a-vat scenario Descartes questioned everything the senses register. Your brain could be inside a vat filled with a life supporting liquid and it could be connected to a computer that generates the impression that you are a person who is walking. This is also the theme behind The Matrix. What is beyond doubt, according to Descartes, is that you exist even if you are just a brain-in-a-vat. And you can establish this fact by thinking. “I think, therefore I exist,” he claimed. Other philosophers like Francis Bacon, Thomas Hobbes, John Locke, and David Hume, believed that knowledge comes from observations. This was a renewed empiricism.

At the time there were great advances in the natural sciences driven by thinking but these advances themselves also spurred thinking. The combination of observation and thinking created scientific progress. This worked more or less as follows. Assume you plan to investigate the effect of gravity on the motion of objects. You can do this by dropping an iron ball from a tower from different heights and measure how long it takes for the ball to hit the ground. The table below shows the measurements.

Height (in metres)Time (in seconds)

It takes some thinking to figure out that the relationship between height and fall time is reflected in the following mathematical formula: fall time = 9.81 * √ (2 * height). For instance, 3.19 = 9.81 * √ (2 * 50.0). If the tower is only 50 metres high then it isn’t possible to measure how long it will take for the ball to fall from 100 metres. But if you know the mathematical formula of the relationship then you can calculate the fall time without measuring it, so: 9.81 * √ (2 * 100) = 4.52 seconds. It is observation and thinking combined that made this possible.

Finding the mathematical formula that matches the data is a bit like fitting the pieces of a jig saw puzzle. This type of reasoning is called induction, which usually is formulating a general rule based upon observations. You can never be sure that the outcome is correct. For instance, on the basis of your own observations with the help of induction you might conclude that all swans are white. On the other hand, deduction is logical reasoning from assumptions to conclusions. If all assumptions are true, and the rules of logic are followed correctly, then the conclusion must be true. Deduction usually is about applying general rules to specific situations. An example is: all men are mortal (first premise) and Socrates is a man (second premise) then Socrates is mortal (conclusion). Also, if the relationship between height and fall time is reflected in the mathematical formula: fall time = 9.81 * √ (2 * height) (first premise), and the height is 100 metres (second premise) then the fall time is 4.52 seconds (conclusion).

Immanuel Kant realised that knowledge arises from observation (empiricism) but that it is impossible to have knowledge without thinking (idealism). Observations have to be interpreted. Thinking imposes a structure upon observations. For example, we do not perceive trees or gravity. These are categories of human thought that we attach to the world. We do not know and cannot know what reality is like (relativism). The things themselves remain unknown so metaphysical speculation about the nature of reality is pointless, for instance asking yourself whether or not gravity is real or imagined. This was one of the greatest advances in knowledge theory in 2,000 years. It is a synthesis of previous thoughts that can be seen as a higher level of insight. Such major leaps in philosophy are extremely rare.

Subsequent idealist philosophers argued that absolute knowledge is possible because the mind creates reality. They argued that reality is subject to the mind so reality can be uncovered with reason. For instance, the fall of a ball is subject to mathematical laws invented by the human mind. Georg Wilhelm Friedrich Hegel believed that history is a dialectic process resulting in progress. In science and philosophy a reasoned debate of ideas in the form of argument and counter argument could lead to a higher insight called synthesis. It doesn’t seem an accident that Hegel came up with this just after Kant had upset knowledge theory by coming up with such a synthesis.

Contemporary philosophy

Kant more or less had ended metaphysics or the speculation about the nature of reality. Philosophers became less ambitious. One reaction was pragmatism. Evolution theory suggests that we hold the beliefs that help us to survive and reproduce. American thinkers such as Charles Sanders Peirce and William James viewed thinking as a means of solving problems. They weren’t interested in truth or the nature of reality. Another approach, hermeneutics, with thinkers like Wilhelm Dilthey and Martin Heidegger concerns itself with interpreting human communication. Dilthey argued that natural sciences are about interpreting observations while humanities are about understanding meaning expressed in communication. Heidegger goes a bit further by claiming that the essence of human existence is understanding.

There was also a renewed search for the foundations of knowledge. Analytical philosophers like Bertrand Russell and Ludwig Wittgenstein believed that the main tools of philosophers are language and logic. Their aim was to develop a new method to gather certain knowledge of reality. They assumed that there is an outside world and claimed that language can be used to express facts that correspond to elements of reality. This is called realism. It is related to empiricism. They claimed that there are justified true beliefs. So if Jane believes something to be true, and it is indeed true, her belief is justified. The main problem here is that this doesn’t clarify which facts are true and justified.

Karl Popper then came up the concept of falsification, which was a significant advance in knowledge theory. He believed that ideas can never be proven but that they can be falsified if there is contradicting information. For instance, you may believe that all swans are white until you spot a black swan. From then on, you may believe most swans are white and some are black. This is how knowledge progresses. The belief that most swans are white and some are black is closer to the truth than that all swans are white, even though it may still not be true if there is a red swan somewhere out there no-one has ever seen.

This is also how science progresses. Scientific theories must be falsifiable, meaning that they can be used to do predictions that you can check. For instance, the mathematical formula reflecting relationship between height and fall time can be used to predict the fall time from 100 metres. And if you do an experiment and the outcome is different than the formula indicates, the theory is falsified, unless your measurement is inaccurate, which is probably the case.

Edmund Gettier attacked the notion of justified true beliefs. For instance, if Jane looks at her watch and it says that it is two o’clock she may believe that it is two o’clock. What she doesn’t know is that her watch stopped exactly twelve hours earlier. Her belief is therefore not justified. But because the watch stopped twelve hours ago it accidentally gives the correct time so that her belief is nevertheless true.

As our knowledge increased over time our understanding of reality also changed. These changes are often driven by scientific discoveries. This also applies to science itself. Thomas Kuhn noted that the history of science is characterised by a succession of paradigms. Only 500 years ago most people in Europe believed the Earth is flat, a few thousand years old, and at the centre of the universe. The ancient Greek discovery that the Earth is a sphere was known to educated people. When Columbus set sail to the West, he expected to end up in the Indies (Indonesia). Now most people in Europe believe the Earth is a sphere, billions of years old, and an insignificant spot in the universe.

Post-modernism claims that great stories like religions and ideologies are dead and that there is no absolute knowledge. Words like reality and truth are even seen as totalitarian concepts by post-modernists. There is still room for small stories and fragments of reality but they depend on perspective. A great source of inspiration for postmodernism is Friedrich Nietzsche who proclaimed the death of God and heralded the end of the classic Christian story of God’s people on the road to Paradise that gives meaning to our existence. Postmodernism is just renewed relativism. This view was, not surprisingly, criticised by philosophers who claimed that post-modernism makes it appear that truth is subjective.

And so we are more or less back at the point where Socrates was refuting the sophists. And with the simulation argument the speculation about the nature of reality or metaphysics re-emerged. We could all be living inside a computer programme created by an advanced humanoid civilisation. And so it may seem that knowledge theory has gone nowhere. At least it is obvious that, while our knowledge increased dramatically during the last 2,000 years, knowledge theory didn’t progress accordingly.


There are a few takeaways from what has been discussed so far:

  • The truth or falsity of a statement may depend on whether or not it accurately describes (some part of) reality. With the help of empiricism and induction you may arrive at correct conclusions.
  • The truth or falsity of a system of statements may depend on its logical consistency. Contradictions are evidence of errors. With the help of idealism and deduction you might arrive at correct conclusions.
  • Assertions can always been called into question as the foundations of knowledge itself are questionable. Empiricism and induction as well as idealism and deduction can lead to wrong conclusions.
  • Plausibility can be used to support theories. An assertion is plausible if there is evidence supporting it and there is no evidence contradicting it. In science it often means that the theory hasn’t been falsified.
  • Pragmatism implies that usefulness is more important than truth. For instance, religions make larger scale cooperation possible. Religions allow tribes to grow larger and muster more men for war.
  • Minimalism argues for using as few assumptions as possible to prove a point and not to engage in unnecessary speculation.
  • Finally, there can be progress in thought. Two contradicting arguments can both be correct as there may be a higher level of truth that resolves the contradiction. For instance, the simulation argument can resolve the contradiction between creation and the big bang and evolution theories.

There is difference between proof and evidence. In common language these terms are used interchangeably. Proof is a final verdict that removes all doubt whereas evidence only supports a particular explanation. Proof is usually achieved by deduction while evidence is often used in induction. Proof is an idealist concept. For instance, in mathematics proof is possible as it often comes down to pure deductive reasoning that doesn’t involve an outside reality. Evidence is often related to empiricism. Applying idealist concepts to reality is problematic as general rules like the relationship between height and fall time used in deduction are usually attained through induction.

Featured image: Owl eyes. Brocken Inaglory (2006). Public domain.

Other image: Brain-in-a-vat. Alexander Wivel (2008). Public domain.

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