Knowledge theory

What is knowledge theory?

What is truth, and what is knowledge? Philosophers have been discussing these questions for thousands of years. Knowledge theory is also called epistemology. It is about the nature of knowledge. It deals with truth, belief, and the justification of beliefs. It aims to answer questions such as: What do we know? What does it mean that we know something? And what makes beliefs justified? We usually acquire knowledge in two ways:

  • by induction, which is using observations to formulate general rules or theories and
  • by deduction, which is applying these general rules and these theories to specific situations.

For instance, after carefully observing the available records of all the people that have lived and still live, you arrive with the help of induction at a general rule that people die before turning 120 years old. Then, using this rule and deduction, you infer that you will die before the age of 120. That seems straightforward, but there are lots of pitfalls. That is why philosophers are still discussing these issues.

There is a difference between rules and theories. A rule is that if A occurs, B happens. A theory is that A causes B. And if we cannot observe A, the theory assumes the existence of A. For instance, an explanation of electricity assumes the existence of electrons. We cannot see electrons, not even with a powerful microscope, so we presume that electricity proves their existence.

This treatise on knowledge theory is a historical account as new ideas usually build upon previous thoughts. It discusses Western philosophy as Western thinkers have been the most inquiring. As a result, the scientific revolution took place in the Western world. Science is the result of thinking but has also greatly influenced thinking. And so, this approach is the easiest way to tackle the most relevant topics.

Classical philosophy

The ancient Greek philosophers already speculated about the nature of reality. Some believed that everything consisted of four ingredients: fire, water, earth and air. Later on, a few philosophers argued that the building blocks of reality are small particles called atoms. These atoms differ in size and shape. The objects we see are groups of atoms stuck together. That was already close to the modern understanding of reality. This kind of speculation is called metaphysics. It is speculation because atoms are invisible, but by assuming that atoms exist and have different shapes and sizes, you can explain the presence of different types of substances.

There were other issues the ancient Greeks were pondering. Some figured that the earth is a sphere. They could infer it by looking at the sea. The sea horizon is slightly curved, while boats disappear in the distance before their sails do. A philosopher named Xenophanes doubted religion. He realised that people believed that the gods were like themselves. For instance, black people thought that the gods were black, while red-haired people believed the gods were red-haired. Xenophanes then claimed it was not possible to know the gods and how they looked. It was an early form of scepticism.

And why would you worship the Greek gods if the Persians and the Egyptians have other gods? If your place of birth determines what you believe, 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 view is called relativism. Socrates is known for his dialogues in which he debated with the sophists.

According to Socrates, there is absolute truth even though we do not know it. His pupil Plato later claimed that ideas are the basis of knowledge and that ideas, not objects, are the building blocks of reality. His view is called idealism. Plato’s pupil Aristotle asserted that knowledge comes from observations. His approach is called empiricism. Both methods come with problems. If you imagine a unicorn, you have the idea of a unicorn, and the idealist could claim that unicorns exist. On the other hand, if you see a unicorn after eating some mushrooms, the empiricist could reason that unicorns exist.

And so, knowledge can always be called into question. If no one has ever seen a unicorn, this still is not definite proof of their non-existence. These creatures could still be hiding deep down in the forests. And perhaps the consumption of mushrooms improves your perception. It is for that reason that scepticism emerged. In ancient times there were two groups of sceptics. The first claimed that nothing is certain. They aimed at refuting the claims of other philosophers. The second argued that it is better to postpone judgement until the matter is sufficiently clarified.

These ideas were revived in Europe in the late Middle Ages after the texts of the classical philosophers had turned up in Arab libraries. European philosophers like Thomas Aquinas and William of Ockham were also theologians. They believed that there is no difference between theology and science. Over time science and religion became separated. Science became based on observations and reason. Religion was a result of divine revelation.

William of Ockham is known for his simplicity principle named Ockam’s Razor. It states that if several hypotheses can explain a phenomenon equally, the one that comes with the fewest entities should be selected. Entities can be assumptions that need to be true. Ockam’s Razor is an argument for minimalism in reasoning or preferring obvious explanations if they suffice. So, if you intend to prove a point, you better use as few unproven assumptions as possible.

Modern philosophy

After 1500 AD, European thinkers realised that Christopher Columbus had discovered an entirely new continent. It became clear that traditional knowledge had failed dramatically. Nothing in the Bible or other ancient sources indicates that America exists. At the same time, Protestants began to challenge the authority of the Roman Catholic Church by making religion a personal matter. The ensuing religious wars ravaged Europe, and they ended without a clear winner. The question arose as to how to evaluate the claims of the different branches of Christianity. After all, they cannot 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. This school is called rationalism, but it was a new branch 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 connected to a computer that generates the impression that you are a person who is walking. What is beyond doubt, according to Descartes, is that you exist, even when you are just a brain-in-a-vat. And you can establish this fact by thinking. ‘I think therefore I exist,’ he concluded. Other philosophers like Francis Bacon, Thomas Hobbes, John Locke, and David Hume argued that knowledge comes from observations. It was a renewed empiricism.

It was an era marked by advances in the natural sciences. These advances were the result of thought, and they, in their turn, spurred further thinking. It was the combination of observation and thought that led to scientific progress. For example, you can investigate the influence of gravity on the motion of objects by dropping an iron ball from a tower. If you release the ball from different heights, you can measure how long it will take for the ball to hit the ground. The table below shows the possible results of these measurements.

Height (in metres)Time (in seconds)

It requires considerable thought to figure out the formula representing the relationship between height and fall time. This formula is: fall time = 9.81 * √ (2 * height). For instance, 3.19 = 9.81 * √ (2 * 50.0). If the tower is only 50 metres high, you cannot measure how long it will take for the ball to fall from 100 metres. With the help of the formula, you can calculate the fall time without the need for 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 like fitting the pieces of a jigsaw puzzle. This way of reasoning is called induction. It is about producing a general rule with the help of observations. You can never be sure that the outcome is correct. For instance, using your sightings and with the help of induction, you might conclude that all swans are white. And if you go to the Moon to drop an iron ball from a tower over there, you will discover that the relationship between height and fall time is different.

Another way of reasoning is deduction. It is working from assumptions to conclusions using logic. If the premises are all true and the rules of logic are correctly applied, then the inference must be correct. Deduction usually is about applying general rules to specific situations. For example, if all humans are mortal (first premise), and Socrates is a human (second premise), then Socrates is mortal (conclusion). Also, if the relationship between height and fall time is: fall time = 9.81 * √ (2 * height) (first premise), and the tower is 100 metres (second premise), then the fall time is 4.52 seconds (conclusion).

Immanuel Kant realised that knowledge arises from observation (empiricism), but it is impossible to know without thinking (idealism). We interpret observations. Our thinking imposes its structure upon these observations. Furthermore, we do not know what reality is (relativism). We do not perceive trees or gravity. These are categories of human thought we attach to the world. The things themselves remain unknown. Hence, metaphysical speculation about the nature of reality is pointless, for instance, asking yourself whether or not gravity or electrons exist. It was a synthesis of previous thoughts and a higher level of insight. Such major leaps in philosophy are rare.

Subsequent idealist philosophers argued that absolute knowledge is possible because the mind creates reality. Reality is subject to our intellect, and reason can uncover it. For instance, the fall of a ball is subject to mathematical laws invented by the human mind. Georg Wilhelm Friedrich Hegel saw Napoleon annihilating the old order and spreading enlightenment ideas all over Europe. Impressed by these events, he claimed that history is a dialectic struggle of ideas resulting in progress. More generally, a reasoned debate using argument and counterargument can lead to a higher insight called synthesis.

Contemporary philosophy

Kant more or less had ended the idea that metaphysics can be a source of knowledge. Philosophers became less ambitious from then on. One reaction was pragmatism. Evolution theory suggests that we hold beliefs to help us survive and reproduce. American thinkers such as Charles Sanders Peirce and William James viewed thinking as a means of solving problems. They were not interested in truth or the nature of reality. Another approach, hermeneutics, with thinkers such as Wilhelm Dilthey and Martin Heidegger, concerns interpreting human communication. Dilthey argued that natural sciences are about interpreting observations while humanities are about understanding meaning.

There was 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. They aimed to develop a new method to gather knowledge. They assumed there is an outside world and claimed that language expresses facts that correspond to elements of reality. This view is called realism, which is related to empiricism. They claimed that there are justified true beliefs. For instance, Jane might think that something is true. If this is indeed the case, then her conviction is justified.

Karl Popper came up with the idea of falsification. You can never prove that a hypothesis is correct, but you can prove it is wrong when you find contradicting evidence. For instance, you might presume that all swans are white. As soon as you spot a black swan, your theory is proven wrong. Subsequently, you assume that most swans are white while some are black. It is the way knowledge progresses. The belief that most swans are white and some are black is closer to the truth than all swans are white. It may still be incorrect as there could still be a red swan somewhere out there no one has ever seen.

Scientific theories are falsifiable. They allow us to make predictions that we can check. For instance, you can go out and look for swans and check their colour. You can use the mathematical formula reflecting the relationship between height and fall time to calculate the fall time from 100 metres. And if you do an experiment and the outcome differs from the calculation with formula, the theory is proven wrong unless your measurement or computation is inaccurate.

Edmund Gettier criticised the notion of justified true beliefs. You can be correct for the wrong reasons. For instance, Jane looks at her watch that says the time is two o’clock. She believes it. She does not know that the timepiece stopped exactly twelve hours earlier. Her belief is therefore not justified. The watch accidentally gives the correct time, so her belief is true.

As our knowledge increases over time, our understanding of reality also changes. Scientific discoveries drive these changes. It also applies to science itself. Thomas Kuhn noted that there is a succession of paradigms in science. A paradigm is a theory or a system of ideas that dominate a field in science. Usually, it is not possible to explain everything. The theories that clarify the most phenomena, and leave the fewest unexplained, are the best and form the paradigm in the field. For instance, the presumption that swans are either black or white is better than the assertion that they are all white, even if red swans exist.

If you compare reality to a jigsaw puzzle, the paradigm is the solution that makes the most pieces fitting. Unexplained phenomena are pieces without a place in the solution, for instance, unexpected readings on instruments. These readings might indicate that the paradigm is incorrect. As long as no better explanation is at hand, most scientists probably attribute them to errors. At some point, the evidence piles up and cannot be ignored any longer. Then, a scientist might come up with a better hypothesis, and out of the confusion, a new paradigm could arise.

Paradigms in science affect the views ordinary people hold. Only 500 years ago, most people in Europe believed that the Earth is flat, a few thousand years old, and at the centre of the universe. The ancient Greek discovery that the Earth could be a sphere was only known to a few educated people. When Columbus set sail to the West, he expected to end up in Indonesia. Nowadays, most people believe the Earth is a sphere, billions of years old, and an insignificant dot in the universe.

The evidence contradicting existing religions and the failure of ideologies gave rise to post-modernist claims that great stories like religions and ideologies are dead and that absolute knowledge is impossible. Words such as reality and truth became seen as totalitarian concepts. In post-modernism, there is only room for small stories and fragments of realness, depending on perspective. A great source of inspiration was Friedrich Nietzsche. He proclaimed the death of God and heralded the end of the Christian story of God’s people on the road to Paradise giving meaning to our existence. Post-modernism is a renewed relativism. This view was, not surprisingly, criticised by philosophers who claimed that the truth is not subjective.

And so we are more or less back at the point where Socrates was refuting the sophists. With the simulation hypothesis, speculation about the nature of reality or metaphysics re-emerged. We could all be living inside a computer simulation run by an advanced post-human civilisation. And so, it appears that knowledge theory has gone nowhere. At least, it is clear that, while our knowledge increased dramatically during the last 2,500 years, knowledge theory did not progress accordingly.

Data, information, knowledge and wisdom

There is a difference between data, information, knowledge and wisdom. Data refers to signals or symbols like letters or numbers. Data does not need to have meaning. A noise you hear is data. The sequence Q&7nn?9Y is also data. Information refers to what data means. If you know that the noise you hear comes from a car engine, this is information. There is a car with a running engine nearby. Characters together can form words and sentences that can have meaning if you know the context. So, if you read sales are up 25% last month, this can be information, but only if you know the corporation it applies to and when it is written, so that you know the month.

To acquire knowledge, you need information, and it needs to be correct. You may read that the sales are up by 25%, but it does not have to be true. And the noise you hear might be a recording. Wisdom refers to understanding. Knowledge itself does not always lead to better insights and decisions. It can be hard to discern between the important and the insignificant. And so, you may become indecisive when information appears to conflict, or you might ignore information to be decisive.

The amount of data used and stored is growing fast. Most data is not information, but entertainment, for instance, cat videos on YouTube. A small portion may be information like sales data. Whether or not data is information depends on your objective. For any investigation, only a fragment of the available data is relevant. It requires wisdom to understand which data is helpful and what it means for the inquiry. The amount of data increases faster than the amount of information. The amount of information increases faster than knowledge. And wisdom cannot be measured.

Proof and evidence

Proof and evidence are not the same, even though we use these words interchangeably. The definition of proof is a final verdict that removes all doubt, whereas evidence only supports a particular explanation. Proving is usually done by deduction, while induction works with evidence. Proof requires the premises to be correct, which is problematic. The premises used in deductive reasoning, for instance, the relationship between height and fall time, are attained by induction. In mathematics, proving is possible. It is pure deductive reasoning without applying it to reality. For instance, 1 + 1 = 2 is always true. But if you think you see two trees, someone else may not agree. Perhaps, the other person sees three trees or only bushes.

Evidence is related to empiricism. Only, you may not have all the information. With a limited sample of swans and induction, you could conclude that all swans are white. We support claims about reality with evidence, for instance, experiments, but we cannot be sure that relationships like those between height and fall time are always the same.

Hence, there is no proof in reality, not even in science, but scientific evidence meets specified quality standards. The scientific method involves careful observation and rigorous scepticism. That is because observations involve our fallible senses. It further includes formulating hypotheses via induction based on the observances, followed by testing deductions made with the theses using experiments and measurements.

The words establish and conclude can bridge the gap between proof and evidence. They denote achieving the best explanation for the observations. The observations need to be reliable. Only, it may be impossible to use a theory like this universe being a simulation to make testable predictions. A hypothesis needs evidence, and must explain the observations better than the alternatives. By assuming that this universe is a simulation, we can explain phenomena that would otherwise remain unexplained.

Something similar happens in science. No one has ever seen electrons, but by postulating their existence and behaviour, we explain electricity. The simulation hypothesis can explain the paranormal in cases where claims of fraud and delusion fail to be convincing. The main difference is that assuming the existence of electrons allows us to make predictions that we can subsequently test in experiments. Paranormal phenomena tend to be unpredictable, so the simulation hypothesis is not scientific.


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

  • We can always debate assertions because the foundations of knowledge themselves are questionable. Empiricism and induction but also idealism and deduction can lead to wrong conclusions.
  • The truth or falsity of a statement depends on whether or not it accurately describes (some part of) reality. With the help of empiricism and induction, you might arrive at better conclusions.
  • The truth or falsity of a system of statements depends on its logical consistency. Contradictions are evidence of errors. With the help of idealism and deduction, you might arrive at better conclusions.
  • An assertion is plausible if there is sufficient evidence supporting it and no evidence contradicting it. In science, it often means that experiments support the theory and no experiments contradict it.
  • Pragmatism implies that usefulness is more important than truth. For instance, religions make large-scale cooperation possible. Religions allowed tribes to grow larger and muster more men for war.
  • Minimalism argues for using as few assumptions as possible to establish a point. It prompts us not to engage in unnecessary speculation or to use irrelevant data.
  • There can be progress in thought. Contradicting arguments can be correct in their own right as there could be a higher level of truth or synthesis resolving the contradiction. For instance, the simulation hypothesis may resolve the contradiction between the religious idea of creation and the big bang and evolution theories.
  • Proof means the absence of doubt, which is not possible when we deal with reality. Evidence can support a particular explanation or theory. In the absence of proof, one can look for the best available explanation for the observations.

Latest revision: 10 May 2022

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

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

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