Delimitation problem

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The problem of demarcation , also called the problem of demarcation , asks in Karl Popper's philosophy of science for a criterion according to which claims (sentences, sentence systems) of empirical science can be distinguished from statements of logic , mathematics , metaphysics or myths . Popper suggests choosing the falsifiability of a statement using basic sentences as a delimitation criterion .

According to Popper, David Hume had already worked on the problem, but it was only through Immanuel Kant that the question of the limits of scientific knowledge became the focus: "... what and how much can understanding and reason, free of all experience, know ...". That is why Popper originally proposed the term "Kant's problem". However, he later emphasized that the limit of empirical science does not represent the limit of what can be reasonably and rationally debatable. Already Aristotle , however, had indicated a criterion according to which the empirical science like mathematics, however, treated in time variable, not empirical sciences the unchangeable.

Falsifiability / refutability

Main article: Falsificationism

For Karl Popper, Humean's "problem of induction " is the question of the validity of the laws of nature. It arose from the apparent contradiction between the “basic thesis of empiricism ”: Only experience can teach us about the truth or falsity of a statement about reality.

Popper proposed to solve the question, to drop the implicit requirement that sentences must be fully decidable. Instead, he regards laws of nature and theories as "partially decidable", i. H. Although not verifiable, it can be falsified or criticized by empirical facts. In his early remarks on this he presented a very radical modification of Einstein's dictum (which equated the theoretically describable reality with the falsifiable, a position that he later no longer took):

"Insofar as the propositions of a science relate to reality, they must be falsifiable, and insofar as they are not falsifiable, they do not relate to reality."

For Popper, this results in the falsifiability of an assertion through empirical facts as a delimitation criterion.

"An empirical-scientific system must be able to fail because of experience."

The falsifiability criterion has firstly to do with the logical structure of statements (how they can logically fail) and secondly with their methodological use (how they can be made to fail because of experience).

Popper's problem of demarcation should not be confused with the problem previously discussed in the Vienna Circle , which goes back to Ludwig Wittgenstein , namely: how to distinguish meaningful sentences from nonsense (“ verification criterion of sense ”).

Popper's solution to the questions of induction and delimitation results in the following consequences:

  1. Metaphysical statements are not declared meaningless in advance.
  2. Laws of nature, because they are neither definitively verifiable nor falsifiable, are nothing more than presumptive knowledge: Strictly speaking, they do not form a “system of our knowledge” but a “system of hypotheses”.

The criterion for when a theory is empirical or has empirical content (i.e. when it makes a scientific statement about reality) has also established itself outside of the critical rationalism developed by Popper , albeit only partially and in a more or less modified manner Shape.

In analytic philosophy it appears as a refutability criterion. A thesis that in principle cannot be falsified is considered non-scientific because it does not make any statements that can be verified by empirical observations or makes no falsifiable predictions. Therefore every analytical result and every empirical finding can be taken as evidence to confirm such a thesis.

Establishing falsifiability as a central criterion for scientific research means that hypotheses and theories must always be testable. If falsification is not possible, foreclosure occurs, i. H. Immunization against alternative viewpoints and conflicting facts. However, not every experimental refutation means that a scientific teaching must be given up. For example, the methodological correctness of an experiment can be questionable. It is also possible to introduce supporting hypotheses that back up a theory. Example: To determine the orbit of Uranus, astronomers applied Newton's law of gravity. However, the observations contradicted expectations. Instead of now considering Newton's law refuted, they formed the ad hoc hypothesis that there must be another, as yet unknown planet, which was later confirmed. The introduction of ad hoc hypotheses reduces the degree of falsifiability of an empirical statement. In the logic of research, Popper therefore proposed the rule to completely dispense with ad hoc hypotheses. The scientific theorist Imre Lakatos, on the other hand, took the view that a theory (or a research program) should only be regarded as "degenerate" and thus unscientific if it is refuted in practically every significant test.

Other demarcation criteria

In addition to the criterion of falsifiability in the philosophy of science, other criteria so by the proposed order science from non-science delineate positivism the induction and verification . For Martin Gardner , confirmation of a theory through evidence and the competence of the researcher is crucial. Paul R. Thagard suggests the existence of the factors theorising, research community and historical context as demarcation criteria. The science historian Thomas Samuel Kuhn emphasized progress in terms of a progression of different phases. He rejected Popper's suggestion of falsifiability for demarcation and only took up the demand for concrete predictions. Instead of falsifiability, he suggested the possibility of further development as a delimitation criterion. Within a theory, it must be possible to do normal science , that is, to solve smaller problems within the chosen paradigm ("puzzle solving"). This improvement is precisely not possible with non-scientific teaching. He writes about astrology : They had rules to apply, they had no puzzles to solve and therefore no science to practice. Imre Lakatos sees the progressiveness of a research program as the key criterion.

Martin Mahner advocates a delimitation based on a checklist that can be adapted to specialist areas, but does not constitute a strict criterion. He justified this with the need for the citizens of a civilized and educated society to make scientifically informed decisions. Regardless of where the line of a delimitation criterion is drawn, Mahner considers it important to draw a line in order not to lapse into relativism , arbitrariness and irrationalism .

Requirements for empirical statements

The following criteria (target specifications) that the statements of an empirical science should meet are cited by various currents in the theory of science:

  1. Internal consistency : Hypotheses or theories should not have any logical contradictions in their structure.
  2. External consistency : Hypotheses or theories should be compatible with knowledge that has already been accepted (external consistency ) or indicate where knowledge that was previously assumed to be certain should be corrected in your sense.
  3. Meaningfulness : A theory should be as meaningful as possible and make as many and precise forecasts as possible, i. H. As many logical sentences as possible should contradict the theories or hypotheses, the theory should therefore prohibit as much as possible.
  4. Comprehensibility : Theories and hypotheses should be formulated in as simple and clear language as possible.
  5. Provisionality : The formulation of theories and hypotheses should reveal weaknesses as far as possible and not pretend certainty where there cannot be any.


  1. "The task of finding such a criterion by which we can delimit empirical science from mathematics and logic, but also from 'metaphysical' systems, is what we call the problem of delimitation." (Karl R. Popper: Logic of Research. Vienna 1935 . Chapter 4: The problem of demarcation ) Popper only mentions metaphysics in part (Karl Popper: Zwei Mitteilungen über Induktion und dembegrenzung (1933-1934) . In: Karl R. Popper: Logic of Research. Tübingen 8th verb. And verm. Ed. 1984. ISBN 3-16-944778-5 . P. 255), partly also pseudoscience and myths. (Herbert Keuth, (Ed.): Karl Popper: Logic of Research 3rd, edited edition, 2007. ISBN 978-3-05-004368-5 , p. 43)
  2. ^ Karl R. Popper: Logic of Research. Vienna 1935, Chapter 4: The problem of demarcation
  3. Immanuel Kant: Preface. Critique of Pure Reason. Work edition, ed. by Wilhelm Weischedel, Vol VI, Frankfurt 1st edition 1974. p. 16. ISBN 3-518-27655-7 .
  4. K. Popper: Objective knowledge. Hoffmann and Campe (1993). ISBN 3-455-10306-5 , chapter 2, note 9
  5. ^ John Losee: A historical introduction to philosophy of science. Oxford University Press, 1977. p. 14
  6. ^ A b Karl Popper: Two communications on induction and demarcation (1933-1934). In: Karl R. Popper: Logic of Research. Tübingen 8th verb. u. probably edition 1984. ISBN 3-16-944778-5 . P. 256
  7. ^ Karl R. Popper: Logic of Research , Tübingen 8. verb. u. probably edition 1984. ISBN 3-16-944778-5 . P. 15
  8. Hans Jürgen Wendel: The problem of demarcation (Chapter I., Section 4). In: Herbert Keuth, (ed.): Karl Popper. Logic of research. Akademie Verlag Berlin 1998. ISBN 3-05-003021-6 . P. 46
  9. ^ Karl Popper: Two communications on induction and demarcation (1933-1934). In: Karl R. Popper: Logic of Research. Tübingen 8th verb. u. probably edition 1984. ISBN 3-16-944778-5 . Pp. 254-256; see. P. 15, note * 3
  10. ^ Karl Popper: Two communications on induction and demarcation (1933-1934). In: Karl R. Popper: Logic of Research. Tübingen 8th verb. u. probably edition 1984. ISBN 3-16-944778-5 . P. 258
  11. Wolfgang Balzer: Science and its methods. Basic concepts of the philosophy of science . Alber, 1997, ISBN 3-495-47853-1 .
  12. see z. B. Richard J. McNally: Is the pseudoscience concept useful for clinical psychology? The Scientific Review of Mental Health Practice . Fall / Winter 2003 Vol. 2 No. 2
  13. ^ Gardner: Fads and Fallacies. In the Name of Science . 1957.
  14. ^ Paul R. Thagard: Why Astrology is a Pseudoscience . In: M. Curd, JA Cover (Ed.): Philosophy of Science. The Central Issues . 1998, pp. 27-37.
  15. ^ Thomas Kuhn: Logic of Discovery or Psychology of Research? 1970, p. 8.
  16. Lakatos: Falsification and the Methodology of Scientific Research Programs. In: I. Lakatos, A. Musgrave, (Ed.): Critique and Progress in Knowledge . 1974.
  17. Martin Mahner : Science and Pseudoscience - How to Demarcate after the (Alleged) Demise of the Demarcation Problem . In: Pigliucci, Massimo; Boudry, Maarten (Ed.): Philosophy of pseudoscience: reconsidering the demarcation problem . Chicago, ISBN 978-0-226-05182-6 , pp. 29-43 .
  18. ^ Martin Mahner : Demarcating Science from Non-Science . In: General Philosophy of Science . Elsevier, 2007, ISBN 978-0-444-51548-3 , pp. 516-575; 571 , doi : 10.1016 / b978-044451548-3 / 50011-2 (English, [accessed March 30, 2019]).


  • Imre Lakatos, Alan Musgrave, (eds.): Problems in the Philosophy of Science. Proceedings of the International Colloquium in the Philosophy of Science London 1965, vol. 3, Amsterdam 1968.
  • Imre Lakatos, Alan Musgrave: Criticism and the Growth of Knowledge. Cambridge 1970.
  • Imre Lakatos: Popper on Demarcation and Induction. in: Paul Arthur Schilpp, (ed.): The Philosophy of Karl Popper. Book I, La Salle, Ill. 1974.
  • Imre Lakatos: The Methodology of Scientific Research Programs. Cambridge 1978.