Popper's three worlds

"World 3" redirects here. For the grouping of countries known as the "third world", see Third world. For the Maoist theory, see Three Worlds Theory. For the system dynamics model used in The Limits to Growth, see World3.
Popper in 1990
Popper in 1990. Karl Popper wrote two papers about the three worlds in the late 1960s.

Popper's three worlds is a theory developed by the British philosopher Karl Popper. It involves three interacting worlds. World 1 is the material realm, World 2 is the mental realm, and World 3 is the cultural realm. Popper's main goal was to defend, through World 3, his notion of objective knowledge against the notion of knowledge as Justified True Belief and inductionism, the idea that laws must be logically (formally) assessed using observations. The methodological rules as well as the logical content of science belong to World 3.[1] Popper's theory is evolutionary. Popper was a strong advocate of a theory of emergence in which each world is not predetermined by previous ones.

Scientific knowledge and inductionism

Already at the time of his major work in philosophy of science, Logik der Forschung (1934), Popper rejected that propositional knowledge could be justified by perceptual experience.[2] From the work of Russell in the early 20th century[3] to that of Lakatos in the late 1960s,[4][5] including that of Carnap[6] and many others, empirical truth (valid correspondence with reality) has played a central role in distinguishing science from non-science. These works attempted to use inductive principles to logically evaluate laws or research programs from observations. Many approaches have been tried and then abandoned.[3][4][6]

Popper argued that the role of evidence or direct experience in science lay not in logical justifications or induction, but in methodological tests aimed at assessing the usefulness of propositional knowledge. Popper emphasized the distinction between the logical and methodological aspects of science.[7][8] The methodological aspect consists of rules that guide the overall scientific process, which includes, for example, the introduction of auxiliary hypotheses not considered in the initial condition to justify a claimed falsification. He was aware that that these rules can hardly be rigorous, because they require methodological decisions, which can be problematic because of the Duhem thesis and other practical implementation issues, whereas the logical aspect is rigorous.[8][9]

Popper further argued that even though deductive logic cannot evaluate empirical truth of laws as the inductivist research program attempted to do,[10] it can nevertheless be an important element in the development of scientific knowledge.[11] Already in the 1930s, Popper wrote that the bulk of scientific activity consists of using deductive logic to check the consistency of a theory, compare theories, check their empirical nature (i.e., falsifiability) and, most importantly, test a theory, which is possible only when it is falsifiable. He emphasized that, even when theories are tested against observations, deductive logic is largely used.[12] Thus, even though Popper's theory abandons the direct logical evaluation of empirical truth, it meets an important expectation of those who value rigorous logic in science, and this in the context of usual scientific activities.

Already in the 1930s, Popper discussed the distinction between scientific objectivity and subjective conviction.[13] It was only decades later that Popper would refer to scientific knowledge as objective knowledge in World 3, and describe this scientific activity as an interaction between World 2 and World 3 responsible for the growth of objective knowledge.[14][15]

Objective knowledge and justified true belief

In the 1960s, reinforced by Tarski's semantic theory of truth, which he saws as a way to describe a correspondence theory of truth, he contrasted the subjective or psychological theory of knowledge with an objective theory of knowledge, in which direct correspondence with reality is a "regulative principle".[16] This correspondence was not a tool for justification, but it clarified the notion of objective knowledge. In the same period, especially after Gettier presented two simple counterexamples to the notion of knowledge as justified true belief,[17][18] the problem of the logical validation of our knowledge, then essentially identified with scientific knowledge,[19] shifted to that of the analytical definition of knowledge in terms of its components: beliefs, truth, justification, and, possibly, other requirements.[17] As early as the late 1950s, Popper expressed the idea that the most interesting problems in epistemology concerned scientific knowledge, not knowledge in general or ordinary knowledge, which he considered too narrow.[20] David Miller noted that, for Popper, knowledge is neither justified nor believed, and that, generally, scientific knowledge is not true (in any logical sense).[21][22]

Popper appreciated the scientific value of analyzing mental states from a biological or psychological perspective, but considered it uninteresting in his epistemology. In particular, he was much impressed by Bolzano's view on objective knowledge.[23] The idea of Popper's objective knowledge is based on the fact that, although the notion of "truth" (in the informal sense of correspondence with reality) is a regulative principle, knowledge is at no point evaluated as true or false in this sense, because Popper accepted the theses of Duhem and Hume, who asserted that this was impossible. Rather, knowledge is considered an objective resource for human beings, just as birds' nests, spiders' webs, and so on, are resources for animals.[24] Therefore, the question of how to reject or accept knowledge in this philosophy is not intended to receive a rigorous answer. A methodology is proposed for that purpose and considered part of objective knowledge, but Popper asserts that it can hardly be rigorous.[25] The methodological rules as well as the rigorous logical content of science belong to World 3.[1] This objective knowledge is evaluated for its usefulness in its applications through critical discussions. This contrasts with the notion of belief, which must also be true, even justified, to qualify as knowledge.[24]

The three worlds

The numbering of the three worlds reflects their temporal order of emergence, each realm emerging as a product of the development of previous realms. A one-word description of each realm is that World 1 is the material realm, World 2 is the mental realm, and World 3 is the cultural realm.[14]

Popper's theory is evolutionary. Popper maintains that at the inception of the universe there was only a "World 1", a realm where everything consisted of physical states and processes. A "World 2" of mental life later emerged as a product of biological evolution. Subsequently a "World 3" of cultural objects emerged as a product of evolution of the human "World 2". Popper was a strong advocate of a theory of emergence in which each world is not predetermined by previous ones. Against this, Popper argues that we should instead see the universe as "creative" and non deterministic, and as having given rise to genuinely new levels or realms - like biological life, "World 2" and "World 3".[26] The three worlds may be understood, in terms of this evolutionary framework, as containing three categories of entity:

  • World 1: the realm of states and processes as studied by the natural sciences. These include the states and processes that we seek to explain by physics and by chemistry, and also those states and processes that subsequently emerge with life and which we seek to explain by biology.[14]
  • World 2: the realm of mental states and processes. These include sensations and thoughts, and include both conscious and unconscious mental states and processes. World 2 includes all animal as well as human mental experience. These mental states and processes only emerge as a product of biological activity by living organisms, and so only emerged subsequent to the emergence of living organisms within World 1. Mental states and processes are the products of evolutionary developments in the World 1 of animal brains and nervous systems, but constitute a new realm of World 2 that co-evolved by its interaction with the World 1 of brains and nervous systems.[14]
  • World 3: the realm of the 'products of thought' when considered as objects in their own right. These products emerge from human "World 2" activity, but when considered as World 3 objects in their own right they have rebound effects on human World 2 thought processes. Through these rebound effects, World 3 'objects' may - via World 2-based human action on World 1 - have an indirect but powerful effect on World 1. In Popper's view, World 3 'objects' encompass a very wide range of entities, from scientific theories to works of art, from laws to institutions.[14][27]

More on World 3

Popper says that his World 3 has much in common with Plato's theory of Forms or Ideas.[24] But, World 3 is not to be conceived as a Platonic realm, because unlike the Platonic world of forms, which is non changing and exists independently of human beings, Popper's World 3 is created by human beings and is not fixed.[28] It corresponds to the current state of our knowledge and culture.[29]

Popper makes two key claims regarding the role of World 3 in the known universe. First, Popper argues that, despite the many continuities and correspondences between the human and animal World 2, (1) only humans consider their mental products as objects in their own right in a World 3 sense and (2) only humans have access to World 3 objects.[24] Second, World 3 has no direct effect on World 1 but only affects World 1 as mediated by the human World 2. For example, a theory of nuclear reactions will never of itself cause a nuclear reactor to be built, yet the existence of a nuclear reactor is not the result of a purely World 1 process but is the eventual product of complex interactions between particular World 3 theories and human World 2 mental activity, and also particular World 2 and World 1 mind-brain-body interactions, leading to particular World 1 human actions (to construct a nuclear reactor) only made feasible by this complex set of interactions.[30]

The interaction of World 1 and World 2

The theory of interaction between World 1 and World 2 is an alternative theory to Cartesian dualism, which is based on the theory that the universe is composed of two essential substances: res cogitans and res extensa. Popperian cosmology rejects this essentialism, but maintains the common sense view that physical and mental states exist, and they interact.[31]

The interaction of World 2 and World 3

An example of interaction between World 2 and World 3 is that, through the process of learning, World 3 transforms World 2. In the other direction, through the publication of scientific results, World 2 transforms World 3. Popper wrote "it is through this interaction between ourselves and World 3 that objective knowledge grows."[32] The entire process of science and its use of deductive logic[12] is part of this interaction. Popper argued that it cannot be studied if this interaction is ignored.

The interaction of World 3 and World 1

The World 3 objects are embodied in World 1. For example, the intrinsic value of Hamlet as a World 3 object is embodied many times in World 1. But, this representation of an object of World 3 in World 1[33] is not considered an interaction in Popper's view. Instead, for Popper, because World 3 is a world of abstractions, it can only interact with World 1 through World 2.[29][34]

See also

Citations

  1. ^ a b Skolimowski 1974.
  2. ^ Popper 2002, Sec. 25.
  3. ^ a b Hay 1950.
  4. ^ a b Zahar 1983, p. 167.
  5. ^ Lakatos 1978, Sec. 1.1, 1.2.
  6. ^ a b Leitgeb & Carus 2024, Sec. 1.6.
  7. ^ Thornton 2016, sec. 3.
  8. ^ a b Popper 1983, Introduction 1982.
  9. ^ Popper 2002, Sec. 23, 65, 68.
  10. ^ Anderson 2006.
  11. ^ Thornton 2016, Sec. 4.
  12. ^ a b Popper 2002, pp. 9–10.
  13. ^ Popper 2002, Sec. 8.
  14. ^ a b c d e Eccles 1970, p. 163–169.
  15. ^ Popper 1972.
  16. ^ Popper 2002b, Chap. 10, Sec. 2.
  17. ^ a b Verhaegh 2025.
  18. ^ Le Morvan 2017.
  19. ^ Wagner 2002, pp. 40–45.
  20. ^ Popper 2002, Preface 1959.
  21. ^ Miller 2011.
  22. ^ Miller 1994, Sec. 3.1.
  23. ^ Boyd 2016.
  24. ^ a b c d Popper 1972, Chap. 3.
  25. ^ Popper 2002, Sec. 23.
  26. ^ Freeman & Skolimowski 1974.
  27. ^ Heller 2011, p. 118–120.
  28. ^ Niiniluoto 2006, p. 61.
  29. ^ a b Eccles 1970, p. 165.
  30. ^ Popper 2012, Indeterminism Is Not Enough: An Afterworld.
  31. ^ 1972, Chap. 6, note 31 and Sec. 23.
  32. ^ Popper 1972, Chap. 3, Sec. 1.
  33. ^ Popper 1994, Chap. 1.
  34. ^ Popper 1972, p. 155.

References

  • Anderson, James (2006-02-01). "The Ethics and Science of Placebo-Controlled Trials: Assay Sensitivity and the Duhem–Quine Thesis". The Journal of Medicine and Philosophy. 31 (1): 65–81. doi:10.1080/03605310500499203. ISSN 0360-5310.
  • Boyd, Brian (2016). "Popper's World 3: Origins, Progress, and Import". Philosophy of the Social Sciences. 46 (3): 221–241. doi:10.1177/0048393116640282. ISSN 0048-3931.
  • Eccles, J. C. (1970). Facing Reality: Philosophical Adventures by a Brain Scientist. Springer Science & Business Media. ISBN 978-1-4757-3997-8.
  • Freeman, Eugene; Skolimowski, Henryk (1974). "Peirce and Popper—Similarities and Differences". In Schilpp, Paul Arthur (ed.). The Philosophy of Karl Popper. Vol. II. Illinois: Open Court. pp. 509–519. ISBN 0-87548-142-6. OCLC 2580491.
  • Hay, W. H. (1950). "Bertrand Russell on the Justification of Induction". Philosophy of Science. 17 (3): 266–277. ISSN 0031-8248.
  • Heller, Michael (2011). Philosophy in Science: An Historical Introduction. Springer.
  • Lakatos, Imre (1978). Worrall, John; Curry, Gregory (eds.). The Methodology of Scientific Research Programmes: Volume 1: Philosophical Papers (1980 ed.). Cambridge, UK: Cambridge University Press. ISBN 0-521-28031-1.
  • Le Morvan, Pierre (2017). "Knowledge before Gettier". British Journal for the History of Philosophy. 25 (6): 1216–1238.
  • Leitgeb, Hannes; Carus, André (2024), Zalta, Edward N.; Nodelman, Uri (eds.), "Rudolf Carnap", The Stanford Encyclopedia of Philosophy (Fall 2024 ed.), Metaphysics Research Lab, Stanford University, retrieved 2025-08-06
  • Miller, David (1994). Critical Rationalism: A Restatement and Defence (1st ed.). Chicago and La Salle, Illinois: Open Court. ISBN 0812691989.
  • Miller, David (2011). "Objective Knowledge". philpapers.org.
  • Niiniluoto, Ilkka (2006). "World 3: A Critical Defence". In Jarvie, Ian; Milford, Karl; Miller, David (eds.). Karl Popper: Metaphysics and epistemology. Ashgate.
  • Popper, Karl (1968) [reprinted in Popper 1972, chap. 3.]. Epistemology Without a Knowing Subject. Third International Congress for Logic, Methodology and Philosophy of Science, 25 August 1967. Amsterdam.
  • Popper, Karl (1972). Objective Knowledge: An Evolutionary Approach (2003 ed.). New York: Oxford University Press. ISBN 978-0-19-875024-6.
  • Popper, Karl R. (1994) [Based on his Emory University lectures 1969]. Knowledge and the body-mind problem : in defence of interaction. Mark Amadeus Notturno. London: Routledge. ISBN 0-415-11504-3. OCLC 30318882.
  • Popper, Karl (1983) [Originally written in 1962]. Bartley, III (ed.). Realism and the Aim of Science: From the Postscript to The Logic of Scientific Discovery. London; New York: Routledge. doi:10.4324/9780203713969. ISBN 0-415-08400-8. OCLC 25130665.
  • Popper, Karl (2002) [1959]. The Logic of Scientific Discovery (2002 pbk; 2005 ebook ed.). Routledge. ISBN 978-0-415-27844-7.
  • Popper, Karl (2002b) [1962]. Conjectures and Refutations: The Growth of Scientific Knowledge. London: Routledge. ISBN 978-0-415-28594-0.
  • Popper, Karl (2012-11-12). Bartley, Iii (ed.). The Open Universe. Routledge. doi:10.4324/9780203713907. ISBN 978-0-203-71390-7.
  • Skolimowski, Henryk (1974). "Karl Popper and the Objectivity of Scientific Knowledge". In Schilpp, Paul Arthur (ed.). The Philosophy of Karl Popper. Vol. II. Illinois: Open Court. pp. 483–508. ISBN 0-87548-142-6. OCLC 2580491.
  • Thornton, Stephen (2016) [First published 1997]. "Karl Popper". In Zalta, Edward N. (ed.). Stanford Encyclopedia of Philosophy (Summer 2017 ed.). Archived from the original on 18 March 2019. Retrieved 19 June 2018.
  • Verhaegh, Sander (2025). "Justified True Belief: The Remarkable History of Mainstream Epistemology". Journal of the History of Philosophy. 63 (2): 285–307. doi:10.1353/hph.2025.a958790. ISSN 1538-4586.
  • Wagner, Pierre (2002-09-18). "Introduction". In Gallimard (ed.). Les Philosophes et la science (in French). pp. 9–65. Retrieved 2025-08-05.
  • Zahar, E. G. (1983). "The Popper-Lakatos Controversy in the Light of 'Die Beiden Grundprobleme Der Erkenntnistheorie'". The British Journal for the Philosophy of Science. 34 (2): 149–171. doi:10.1093/bjps/34.2.149. JSTOR 687447.

Further reading

  • Popper, Karl; Eccles, John C. (1977). The Self and Its Brain: An Argument for Interactionism.
  • Popper, Karl (1994b). Knowledge and the Body-Mind Problem.
  • Popper, Karl (April 7, 1978). Three Worlds by Karl Popper (PDF). The Tanner Lecture on Human Values. Talk delivered at The University of Michigan.
  • Popper, Karl (1994c) [1945]. The Open Society and Its Enemies. Routledge 2012, Princeton University Press 2013.
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