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Theory of knowledge


Theory of knowledge or Epistemology discusses properties of the term "knowledge" and how knowledge may be created.

A summary of the discussion is:

• Do we know anything?
• Can we prove that we know anything?

Suggested answers can be found at the bottom of this page.


Three major, intermixed, views exist:

•  Empiricism
•  Rationalism
•  Skepticism

Existence of knowledge is a core question within philosophy. The discussions concern existence of concepts like truth and reliability and at the outmost border if we know that anything exists at all.


At the website more extensive discussions about knowledge can be found.


What is knowledge?


The concept "knowledge" is related to concepts like "know" and "truth".

This concept "knowledge" is used in various meanings. When the term is used within philosophy, at least one factor ought to be considered important:



Define the meaning of the term "knowledge"!


Philosophers' knowledge - "absolute knowledge"


When used by philosophers, the term knowledge often expresses thoughts that are claimed to be founded on logic exclusively. With such a foundation, knowledge would be unchangeable or eternal. At this website such thoughts are called "absolute knowledge" that should be "absolutely certain" and imply something that we "absolutely know ".

In everyday language we experience matters as being certain. We "know" that the world we observe really exists. We can, and we have to without hesitation, trust many of such arguments, because they are the basis of our survival.

But since the Greek Antiquity it is commonly accepted that knowledge about the world is ultimately based on our perceptions and on conclusions drawn from these. It is therefore accepted that statements about worldly matters do not represent "absolute knowledge" and they are therefore termed probability arguments.


Probability is the very guide of life

Joseph Butler (1736) - The Analogy of Religion, Introduction

Conclusions from clear observations, like "a released stone falls to the ground" will probably always be trustworthy, at least for the time when the stone and earth exist. But more complex conclusions, like that the earth is flat, are less probable and may need to be revised. Both conclusions , however, implies probability arguments.

Philosophers that have tried to claim existence of "absolute knowledge" have until now not been successful in providing any trustworthy example of such knowledge. It hence appears to be impossible to prove the existence of knowledge in the meaning of "absolute knowledge".

When discussing knowledge, philosophers often leave out the term "absolute" . They use terms like "knowledge", "know" and "truth" without definition, and then discuss something that probably is non-existent.


Knowledge - personal experience


We all experience that we learn things in life. We have learnt to walk, to use a language, to write, to use social codes, and learnt a lot of other knowledge from parents, our surroundings and from books.


As our lives are slightly different, this form of knowledge is to some extent individual, and differences in what represents knowledge between individuals may exist.


Knowledge - common experience


There are many examples of groups of people claiming that their common opinions represent knowledge. In a group the claims that the knowledge is correct are strengthened, in spite of that other groups may claim other types of knowledge.

A large part of what we call knowledge, e.g. dogmatic doctrines and sciences, belongs to this category.


A major difference between dogmatic doctrines and sciences is that the claimed observations and conclusions that provide the ground for dogmatic systems may not be questioned, while observations and conclusions within science may be continuously questioned and re-evaluated. This possibility of questioning has resulted in a fantastic development of scientific knowledge.


Knowledge - common experience under continuous revisions


Knowledge may also be said to consist of such observations and conclusions that many persons openly investigate, revise, alter and maybe agree about. This type of knowledge is an adaptation to that "eternal truth" cannot be shown to exist.

For this knowledge to be trustworthy, it is important how it is spread and revised:


•  What type of arguments can be used?
•  How can revisions be encouraged?

From the answers to such questions, something that reminds about what we today call scientific method will probably be created.


Knowledge dependent or independent on experience


As discussed above, the term "knowledge" is not easy to define, and within philosophy this invites to speculation.

A question discussed since the Greek antiquity is whether "knowledge" should be based by observations or if we may reach "knowledge" using only logical reasoning, independent of observations.

Plato discussed that our observations cannot be proven to represent some kind of reality and Aristotle stressed the importance of observation together with logical reasoning (deduction). They both actually had about the same opinions.

And so it has continued through history of philosophy.


During the Enlightenment the concepts became more defined and e.g. David Hume called the two groups, from which our reasoning are built, for "matter of fact" and "relations of ideas".

Reasoning based on "matter of fact" was called probability arguments. Western philosophers today agree about that our experience about the world is ultimately based on such arguments.


Knowledge a priori and a posteriori


It is generally agreed that tautologies ("analytic arguments") represent reasoning a priori. But does arguments in addition to these ("synthetic arguments") exist that also can be said to be a priori?

That is: Does arguments a priori about our experienced reality exist? Without such arguments, the relevance of pure analytic philosophy (armchair philosophy) concerning the world can be seriously questioned.

Kant enters the scene

Without defining his use of the term "knowledge", Immanuel Kant discussed these topics in terms of "a priori" ("knowledge" that can be justified without referring to observations) and "a posteriori" ("knowledge" that requires observations for justification). What he claimed to be a priori arguments is at this website called "absolute knowledge"

Immanuel Kant: public domain
Immanuel Kant (public domain)

Kant wished that abstract philosophy should be justified, and with the help of diffuse definitions he claimed existence of "synthetic a priori arguments".

He hence claimed existence of statements about the world that are not ultimately based on experiences or, differently expressed, that combination of "absolute knowledge" about the world is possible.

A quick conclusion learns that in case we cannot claim existence of any "absolute knowledge" about our world, it is of course impossible to claim existence about combinations of such knowledge. Philosophes, however, dislike quick conclusions. Below three example of longer texts with a similar final conclusion:

• Boghossian P, Peacocke C - New Essays on the A Priori, Clarendon Press (2000).

• Kitcher P, "A priori", Ch. 1 in Guyer P (Ed) - Kant and Modern Philosophy, Cambridge Univ. Press (2006).

• Andersson, H - Apriorisk kunskap, en analys av definitioner, C-uppsats, Lunds Univ. (2007).


Induction - to draw conclusions from observations


Definition of induction:

The process of inferring a general law from the observation of particular instances

Oxford English Dictionary

Short version: Inferring from particulars to generals.


A philosophic attitude that argues for the use of induction is called empiricism.

Induction implies that repeated similar observations create expectations of that additional similar observations under similar conditions will yield similar results, and that they therefore represent something general.

Or in everyday language: When we note something several times, we believe that it is true.

We use induction every day, possibly in every conscious moment. Every morning, we expect the world to look similar to what is was in the evening before - induction! We drink a glass of water and expect it to quench our thirst - induction! We drop a heavy stone and expect it to fall - induction!

We believe that we should look approximately the same and that the floor remains. Induction is the base for all our experience.

Another example of induction is that we believe that every human someday, sooner or later, will die.


Neither induction nor any other method will give rise to "absolute knowledge". Regardless of how many observations we have performed that support a hypothesis, we cannot be certain about that the hypothesis is "absolutely true". This was discussed e.g. by Sextus Empiricus about 200 AD and by Isaac Newton 1730:

It is easy, I think, to reject the method of induction.

For since by way of it they want to make universals convincing on the basis of particulars, they will do this by surveying either all the particulars, or some of them. But

- if some, the induction will be infirm, it being possible that some of the particulars omitted in the induction should be contrary to the universal, and

- if all, they will labour at an impossible task, since the particulars are infinite and indeterminate.

Thus in either case it results, I think, that induction totters.

Annas (Ed.) (2007) - Outlines of Scepticism, Book 2, part XV

As Sextus Empiricus was an advocate of empiricism, it is likely that the term "induction totters" for him implied a rejection of that induction could give rise to "absolute knowledge".


And although the arguing from Experiments and Observations by Induction be no Demonstration of general Conclusions; yet it is the best way of arguing which the Nature of Things admits of, and may be looked upon as so much the stronger, by how much the Induction is more general.

Isaac Newton (1730) - Opticks, 4Ed, p.380


The strength of scientific methodology


An illustration of the problem with induction was given by Bertrand Russell:

There was once upon a time a census officer who had to record the names of all householders in a certain Welsh village. The first that he questioned was called William Williams; so were the second, third, fourth, ...

At last he said to himself: "This is tedious; evidently they are all called William Williams. I shall put them down so and take a holiday."

But he was wrong; there was just one whose name was John Jones. This shows that we may go astray if we trust too implicitly in induction by simple enumeration.

Russell (1945) - History of Western Philosophy, in the section about Francis Bacon

Scientific methodology decreases the insecurity inherent in induction. A scientific treatment of Russell´s illustration may look like this:

• The census officer publishes that all were named William Williams and how he reached this conclusion.

• Somebody reads this and notes that the work is not complete. She checks the church books and finds one John Jones. She reports this, how she arrived to this result and also describes the earlier work by the census officer.

• A person in the village reads this second report and knows that the neighbour, a recent immigrant, is called Sven Svensson. This is reported as a "letter" to a journal. This "letter" also contains references to the two previous reports.

In this manner will, by and by, through induction, verification, falsification and publication, a more refined description of the householders in the village be developed.


Deduction - to infer conclusions by logical reasoning


Definition of deduction:

The process of drawing a conclusion from a principle already known or assumed

Oxford English Dictionary

Short version: Inferring from generals to particulars.


A philosophic attitude that argues for the use of deduction is called rationalism. It is popular within philosophy and is sometimes called "armchair philosophy"

A problem with rationalism is that strict deduction, without references to observations, cannot give anything of interest regarding our perceived reality.

Or differently expressed: Arguments that are synthetic a priori have not been demonstrated to exist. This was discussed in detail by David Hume already at the eighteenth century.

A form of rationalism that is possible to apply while describing our perceived reality therefore must include empiricism.


A more illuminating definition about deductive arguments concerning our perceived world accordingly read:

Deductive arguments concerning our perceived reality create relations between conclusions (ultimately based on perceptions) and perceptions, or between conclusions (ultimately based on perceptions) and conclusions (ultimately based on perceptions).

The link to the definition in Oxford English Dictionary is provided by that "a principle known or assumed" is ultimately based on perceptions.

The logical impossibility of strict rationalism was also discussed by Bertrand Russell:

German philosophers, from Kant to Hegel, had not assimilated Hume's arguments.

I say this deliberately, in spite of the belief which many philosophers share with Kant, that his "Critique of Pure Reason" answered Hume.

In fact, these philosophers, at least Kant and Hegel, represent a pre-Humian type of rationalism, and can be refuted by Humian arguments.

Russell (1945) - History of Western Philosophy", in section about David Hume


Skepticism - we cannot know anything


Skepticism (or Scepticism) has been expressed since the antique Greece. When induction cannot result in "absolute knowledge" and still is the only method of acquiring knowledge about the world, an ancient base for general dismissal of knowledge is created.

The word skepticism comes from the Greek word for "to consider". It implies that an issue should be investigated before arguing about it.

Skepticism, like all other philosophies, exists in varying degrees. When drawn to its extremes it is called Pyrrhonism where it is claimed that we should not trust anything.

Academic or mitigated skepticism includes that some arguments are more probable than other. This later skepticism is strongly connected with empircism and rejects dogmatic and false deductive reasoning.

David Hume is considered as a leading mitigated skeptic, He wrote about Pyrrhonism:


These principles may flourish and triumph in the schools where it is, indeed, difficult if not impossible to refute them.

But as soon as they leave the shade, and by the presence of the real objects, which actuate our passions and sentiments, are put in opposition to the more powerful principles of our nature, they vanish like smoke, and leave the most determined skeptic in the same condition as other mortals.

Hume (1777) - Enquiry p.159

The arguments of Pyrrhonism hence rest on an experienced erroneous foundation. If we, for instance, cannot trust that we are thirsty we have no reason to drink and nature will claim its rights.

Another problem with Pyrrhonism is that supposedly skeptic statements like "Knowledge does not exist", "We can never know anything" or "All is relative" represent contradictions as they, in spite of their content, claim to represent some type of knowledge. A Pyrrhonist can hence never claim his or hers opinion.


Science is not the same as "knowledge":


The term "knowledge" may imply various concepts as discussed above.

Science consists of results from an activity, a method of work, during which observations or conclusions from observations are reported in a manner that admits of examination. This adds to the reliability of a scientific proposition, compared to a proposition that is not based on observations.

Science is hence a concept quite different from "knowledge". The two terms are sometimes confused, probably because many scientific publications are regarded as credible descriptions of our perceived world.


Criticism of science using arguments that rightly should be concerned with the concept "knowledge" is, according to my opinion, either deliberately erroneous or a testimony of unawareness about epistemology.

I view the scientific method as a successful attempt to solve our obstacles with the concept "absolute knowledge".


We use induction, deduction and skeptic arguments


As stated above, we cannot prove presence, or absence of anything using logically strict arguments. We cannot logically prove the presence or absence of a stone, nor the existence, or non-existence, of "absolute knowledge".

We use induction

But we do not seriously believe that the world will change during the time it takes to twinkle. We dare to take a step and put down our foot, without fear that the ground have disappeared.

Hence we apply induction in our lives, probably during every conscious moment. We do that in spite of that we know that "absolute knowledge" about the world cannot be proven using strict philosophical arguments.


We use deduction

During every conscious moment we probably also create relations between observations. Similarities and dissimilarities are judged by our thoughts. Does the food smell as it should? Do I have the strength to move the heavy stone? Do I want to talk to this angry person?

We are mitigated Skeptics

If we reflect, we may sense that we are not entirely certain in our beliefs. Some are more certain, others are less. We believe that the world will exist tomorrow, but we are maybe less certain about that all types of meat are only nutritious.

We have to live with our "truths", even when we cannot prove them to represent "absolute knowledge".


Summary of more than 2000 years of epistemology


• Do we know anything?
- Probably.

• Can we prove that we know anything?
- No, not if the term "know" is taken to mean "absolute knowledge" (but this does not imply that we do not know anything).

• Can we live with that we cannot prove that that we know anything?
- Obviously.


After having written this summary, I became aware of that David Hume formulated the last point in a far more poetic manner:

...who must act and reason and believe; though they are not able, by their most diligent enquiry, to satisfy themselves concerning the foundation of these operations, or to remove the objections, which may be raised against them.

Hume (1777) - Enquiry, p.160