What is Philosophy
What is Philosophy
of Science
Verification and Falsification
about Science
Science according
Paradigm and
paradigm shift
Karl Popper -
Logic and status
Consequences of Popper's theses
Chalmers thing
called Science?
Epistemology -


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?" and "Can we prove that we know anything?".

A summary is given at the bottom of this page.


Three major, intermixed, views exist:

•  Empiricism
•  Rationalism
•  Skepticism

Existence of knowledge is a core question within philosophy. The discussion indirectly concerns existence of concepts like truth and reliability and if we can decide if anything exists at all.


What is knowledge?


The word "knowledge" is related to terms like "know" and "truth".

The term "knowledge" is used in various meanings. When the word is used, at least one factor should be considered to be important:


Define the meaning of the term "knowledge"!


Philosophers' knowledge - "eternal truth" / "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 implying something that we "know absolutely".

Since the Greek Antiquity it is commonly accepted that knowledge about the world ultimately is based on our perceptions and on conclusions drawn from these. At the same time it is accepted that they don't represent "absolute knowledge" and they are referred to as being probable. Conclusions from clear observations, like that a released stone falls to the ground, will by extremely high probability continue to be true as long as 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 are, however, based on probability arguments.

Philosophers that have tried to claim existence of "absolute knowledge" have until now not been successful in giving any today trustworthy example of such knowledge. It hence appears not to be possible to prove the existence, or non-existence, of knowledge in the meaning of "eternal truth" or "absolute knowledge".


More about that "absolute knowledge" cannot be shown to exist


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 different, this form of knowledge is to some extent individual, and differences in what represents knowledge 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 openness 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 a kind of reality, while Aristotle stressed observation together with logical reasoning (deduction). And so it has continued through history of philosophy.


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

Reasoning based on "matter of fact" was called probability arguments. Today western philosophers agree about that our experience about the world is based on probability arguments.


Knowledge" a priori and a posteriori


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"

It is agreed that tautologies and other logical operations ("analytic arguments") are performed a priori. But does arguments in addition to these ("synthetic arguments") exist that also can be said to be a priori, or expressed differently: 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.

Using vague definitions, Kant claimed existence of "synthetic a priori" arguments, i.e. propositions concerning the world that is not based on experience. This has been challenged, and no distinct examples of such arguments have been demonstrated.


... synthetic a priori is now widely regarded as highly questionable

Höffe (2010) - Kants Critique of Pure Reason

Are inherited abilities examples of synthetic a priori "knowledge"


We use logic arguments, or "relations of ideas", at every moment we are awake. But does any experience about the world exist, that could be meaningful to call a priori?

The answer seems to be "No". The closest concept to such knowledge is inherited abilities.


More about inherited abilities


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. When we wake up in the morning, we expect the world to look approximately similar to what is was in the evening before. We believe that we should look approximately the same and that the floor remains. Induction is the base for all our experience.


Philosophical problem


A philosophical problem with induction is that the reasoning (that many similar observations may represent something general) is not logically valid.

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 sure that the hypothesis is "absolutely true". This was discussed e.g. by Sextus Empiricus about 200 AD.


More about induction


An illustration of the term 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", chapter about Francis Bacon

The strength of scientific methodology


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 neighbor, 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, using induction, verification, falsification and publication, a more refined description of the householders in the village is gradually obtained.


Deduction - to infer conclusions by logical reasoning


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"


Philosophical problem


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 more illuminating definition above is illustrated by the by the well-known deduction below:


/premise/ All humans are mortal
/premise/ Socrates is a human,
/conclusion/ Socrates is mortal.


The deduction forms a relation between the premises through the correspondence between properties that form "the concept human" (a compilation of properties, ultimately created from perceptions) and the properties that are shown by Socrates (obtained from perceptions).

It is concluded that because Socrates shares many properties with "the concept human", he may also be suspected to share additional properties contained by this concept.


More about deduction


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", chapter about David Hume

Skepticism - we cannot know anything with "absolute certainty"


Skepticism (or Scepticism) has been expressed since the antique Greece. The relevance of the concept Skepticism is coupled to the definition of the concept of knowledge. When induction cannot result in "absolute knowledge" and still is the only method of acquiring knowledge about the world, and if additionally the claimed deduced descriptions of the world are unfavorable and/or appear to be improbable, a 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 is coupled to empiricism and rejects dogmatic and often deductive reasoning.

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

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

Philosophical problem


The arguments of Pyrrhonism may appear logically irrefutable, but rests 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.


Mitigated Skepticism


During later stages of Plato´s Academy a mitigated, or Academic, Skepticism rose. It argued that some conclusions about reality are more probable than other. This Skepticism was advocated e.g. by David Hume and is the philosophy behind scientific methodology.


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 examinations. 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.

Hence 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" implies to own "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 writing this summary, I became aware of that David Hume formulated the last point in a 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



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