What is Philosophy
What is Philosophy
of Science
What is Verification
and Falsification
about Science
Science according to
Scientific method
Paradigm and
paradigm shift
Karl Popper -
Logic and status
Consequences of Popper's theses
Alternative Science
Chalmers: What is this
thing called Science?
Epistemology -
induction deduction


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 eternal truth. Then he claimed that falsifications could provide us such truth.

It is clearly expressed by Popper himself that he discusses the content of arbitrary statements. But, is a statement unsupported by verifications interesting at all? His argument centers on that an arbitrary statement that is possible to falsify is more interesting than a statement that is impossible to falsify, which sounds reasonable when dealing with statements that are not, and cannot be, verified.

Popper also expressed the remarkable opinion that his discussion about arbitrary statements should be possible to use for a definition of the term science, and this statement has achieved many followers within parts of the academic world that are reluctant in accepting the value of verifications and the scientific method.



The contents of Popper's "science philosophy"


A summary of significant statements in the book:
Popper, Karl - The Logic of Scientific Discovery (1959)
ISBN: 978-0-415-27844-7.

Knowledge are science 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 is 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 fulfilsl 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

Later Popper discusses what criteria should be used to judge if a hypothesis is scientific or not (part 1.6):

• 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.




Falsifiability defines a hypothesis as scientific

Comment by

Falsifying a statement is equivalent to verifying the negation of the statement.



Comments about

Induction does not give eternal knowledge

Scientific reports almost exclusively builds 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" likely meant "eternal truth"). It is a well known fact that induction cannot provide us with "eternal truth". It even appears impossible to argue that "eternal truth" actually exists. Popper erroneously claimed that science is equal to "knowledge" or "eternal truth" (see below).

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

Popper then claimed to solve this erroneous conclusion by introducing yet another logically erroneous inference (see below about verification): When verifications are not valid in the definition of science, it must be falsifications that are valid.

Hence he tried to claim his own definition of the term "Science", building on falsifications.


Verification in Popper's science philosophy - logical error

Popper's discussion contains at least one error of logic that renders the reasoning untenable.

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

In the page about falsification of 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.


Scientific results are not knowledge

An error in Poppers logic 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. Scientific results are existing results created by human activity, while the concept "knowledge" is not easy to define, as discussed in the page of Epistemology.



Science is 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 does not consist of unsupported statements or specific areas of interest, but reported, carefully described observations that are possible reproduce.

Because Popper discusses hypotheses, i.e. arbitrary statements, it appears suitable to summarize Popper's discussions, not as a wish to define the term "Science", but as a test method to sift 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" .

A hypothesis is nothing but an arbitrary statement

As it only consists of an arbitrary statement, a hypothesis is neither scientific nor not scientific.

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.

An example of this view was described by Karl Pearson in the book "Grammar of Science" (Adam and Charles Black, London, 2 Ed., 1912, page 12):

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


To discuss if an isolated statement or an area of interest is scientific or not is to miss by far what has been described and shown to work within science during several hundred years.




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).

Additional examples are given at About - Experience.


Popper's status within philosophy of science

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

Within professional philosophical circles, Karl Popper seems to be outdated.


The citations below are taken from the introduction in the book:
Boyd, R et al. - The Philosophy of Science (1991)
ISBN-13: 978-0-262-52156-7


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.


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 probably describes this in the book "Vetenskapsteoretiska grunder" (pages 139-140, Studentlitteratur 2003). Unfortunately no precise source is given.


"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.

                            (translated by



in reality

Some specific examples according to Poppers discussions are found here  

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