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Karl Popper


Karl Popper is often cited in connection with Philosophy of Science. He claimed that he discussed the contents of the term science by using only deductive arguments.

As discussed below, Popper claimed that verifications are not interesting, as they cannot be proven to supply us with absolutely certain truths. Then he claimed that falsifications could provide us with such truth.

He claimed that he discussed the content of arbitrary statements. But will a statement that is not supported by verifications ever be interesting?


His argument is focused around that a statement that is possible to falsify should be more interesting than one that is impossible to falsify, which sounds reasonable when verifications are ignored.

Popper also expressed the remarkable opinion that his discussion about arbitrary statements should be possible to use for a definition of the term science,

This opinion has achieved several followers within parts of the academic world that are not working according to the scientific method.


Popper's "science philosophy"

Below follows a summary of significant statements in the book: Popper (1959) - The Logic of Scientific Discovery:


Knowledge is scientific results

•...the logic of scientific discovery, or the logic of knowledge... (part 1, introduction).
• The theory of knowledge... may accordingly be described as a theory of the empirical method... (part 1.5).
• ...epistemology, or the logic of scientific discovery... (part 2, introduction).


Empirical science consists of theories

• The empirical sciences are systems of theories (part 3, introduction).


Induction does not exist

• ...I reject inductive logic... (part 1.4).
• Theories are, therefore, never empirically verifiable.
(part 1.6).
• ...denying...that there is such a thing as induction in the... inductive sciences... (part 1.6, footnote).


Popper's "fundamental problems"


Denying induction

Popper starts with a discussion about induction. He points out the well-known fact that we cannot acquire "true knowledge" using induction (part 1.1).

Proposes deduction

Then he proceeds with arguing about deductive creation and testing of a hypothesis (part 1.3):

• A tentative statement is created from a new idea and not from observations (" anticipation, a hypothesis, a theoretical system..."). From this statement logical conclusions are drawn. In this manner a hypothesis is created.

• The hypothesis is tested to see if it fulfils criteria of being a new scientific theory.

• The conclusions that can be derived from the theory are finally tested empirically.


Criteria for hypotheses being scientific

Popper then discusses criteria for when a hypothesis should be regarded as scientific (part 1.6). His statements may be summarized in four points:

• A theory must be either verifiable or falsifiable in order to judge its "truth and falsity".

Induction does not exist and hence not verification. We therefore cannot verify if a hypothesis is scientific.

• As we cannot verify whether a hypothesis is scientific it must, from the two statements above, be the possibility to falsify the hypothesis that determines if it should be regarded as scientific.

• Every statement that is possible to falsify is a scientific theory.




Induction does not give "absolute certain truth"


Scientific reports almost exclusively build on observations and induction (verification).

In company with skeptics for more than two thousand years, Popper denied induction as a source for "knowledge" (where he with "knowledge" meant "absolute certain truths").

It is a well-known fact that induction cannot provide us with "absolute certain truths". It even appears impossible to argue that such truths actually exist. Popper erroneously claimed that science is equal to "knowledge" or "absolute certain truth" (see below).


Popper then claimed that as induction cannot give us "knowledge", and "knowledge" is science, induction (verification) cannot be valid in defining what is science.

He then claimed to solve this erroneous conclusion by introducing yet another logically erroneous inference:

As verifications are not valid in order to define science, it must be falsifications that are valid.

At a closer look these illogical inferences lead to various absurd consequences.


Internal logic error


Karl Popper initially rejects verifications. Later, he suggests a definition of the word science based on falsifications.

At Verification and Falsification at this website, it is shown that a falsification of a hypothesis is equal to a verification of the negation to a hypothesis.

Hence Popper initially rejects existence of verifications. He then uses verification (of negations) in order to suggest a meaning of the word Science.


Philosophical systems of theories may concern our reality or some alternative to it. The only general demand to be laid on such systems is that they should be internally logically correct, i.e. that the theories must not be mutually contradicting.

As discussed above, denial of verifications and affirmation of falsifications implies an internal logical error.


Scientific results are not knowledge


Another error in Popper's argumentation is that he confuses scientific results with "knowledge".

The theory of knowledge... may accordingly be described as a theory of the empirical method... (part 1.5).

Use of these two words interchangeably is obviously erroneous.


Science is an existing result from human activity, while the concept "knowledge" in writings of Popper implies "absolutely certain knowledge"; a concept that is hard to define (as it is probably non-existent).

This is discussed at the page Epistemology.


Science is results of a method of work, not a dogmatic hypothesis


Popper claimed that a statement (hypothesis) or an area of interest could be regarded as scientific or not. He promoted a kind of rule (falsifiability) by which the statement or area should be tested for degree of scientific status.

One absurd consequences of this statement is that every statement that is obviously false should be counted as scientific according to Popper. See the page Popper - in reality for more details.

Science has, since the time of Enlightenment, been about something being verified and reported (scientific method). The core in science hence does not consist of unsupported statements or specific areas of interest.


Science is based on reported, carefully described observations that are possible reproduce.

Because Popper discusses hypotheses, i.e. arbitrary statements, it appears suitable to summarize Popper's discussions as a test method to filter off such dogmas that can be immediately rejected.

If Popper's own dogmas should survive such a test may eventually be an interesting evaluation task for students in "scientific method" (they will not).


A hypothesis is nothing but an arbitrary statement


A hypothesis is neither scientific nor not scientific; it consists only of an arbitrary statement.

A hypothesis may, however, be scientifically supported, i.e. expressed as a summary of observations that are reported in a manner that give possibilities to examine the probability of the hypothesis to correspond with our perceived reality.


When Popper discusses if an isolated statement is scientific or not, he misses by far what has been described and shown to work within science during several hundred years.

The unity of all science consists alone in its method, not in its material.

Pearson (1912) - Grammar of Science, p.12.


Popper's status within Swedish universities


Karl Popper's hypotheses are spread within some of the Swedish universities.

One example in Swedish is given by a university home examination in scientific orientation at the institution of Theoretical Philosophy at Lund's University (original address of the document is presently inactive).

Additional examples are given here.

Anti-scientific education at
some Swedish education centers

Update 2018:
During later years, the dominance of Popper at courses and lectures seems to be have faded, and I imagine that the information and the amount of visitors to have contributed to this (although none of the lecturers have yet contacted me and thanked me).

If this assumption is correct it is encouraging that the standard of the university courses is possible to influence by precise information.

The discussions concerning Popper are in spite of this retained on this website as kind of a “guardian against misleading ideology”


Popper's status within professional philosophy of science


Within history of philosophy of science, Popper is placed in the category of verificationists, as is obvious from the discussion above. He himself, however, tried to claim that he did not advocated verificationism.

Within professional philosophical circles, Karl Popper seems to be obsolete:



No discussion of twentieth-century philosophy of science is complete without an account of a variant version of verificationism which, although it has had rather little impact on recent philosophy of science, has had a deep influence on the thinking of many philosophically inclined scientists and other thinkers.
....but despite these technical difficulties, it remains deeply influential outside professional philosophical circles, perhaps because of its apparent commitment to an antidogmatic conception of scientific inquiry.

Boyd, R et al. (1991) - The Philosophy of Science, p.11.


Popper may have realized his mistakes


Because falsification is equal to verification of a negation, the falsification itself must, according to Popper's hypotheses, be tested using the falsification criterion. During this second falsification, falsification is again needed, and the procedure continues in an infinite regression.

Joakim Molander have presumably discussed this. Unfortunately no reference is given.

Molander (2003) - Vetenskapsteoretiska grunder, p.139-140.

Popper later became aware of these problems and claimed that all observations of phenomena that challenges accepted theories should be treated with the same caution and skepticism as the original theories.


The conclusion is that we cannot even trust falsifications, and then the whole falsificationistic basic statement becomes meaningless. Popper tried to save his theory in this respect by claiming that at some moment we just must decide in believing in a falsification.


The problems finally lead to that Popper abandoned the strong falsificationism and instead viewed science as a continuous process of tests and attempts of falsifications.