Popper's three worlds

Popper's three worlds is a way of looking at reality, described by the British philosopher Karl Popper in a lecture given in August 1967. The concept involves three interacting worlds, called World 1, World 2 and World 3.

Worlds 1, 2 and 3

These three "worlds" are not proposed as isolated universes but rather are realms or levels within the known universe.

Their numbering reflects Popper's view (a) of their temporal order within the known universe, and (b) that the later realms emerged as products of developments within the preceding realm. A one-word description of each realm is that World 1 is the physical realm, World 2 is the mental realm, and World 3 is the cultural realm - though, in the detail of Popper's theory, each "World" or realm transcends what might be typically understood by the respective terms "physical", "mental" and "cultural".

In Popper's theory, there is direct interaction between World 1 and World 2, and between World 2 and World 3, but there is no direct interaction between World 1 and World 3 - World 3 does affect World 1 but only indirectly, through the workings of World 2 with World 3 content and then World 2's subsequent interaction with World 1.

Though it is part of Popper's theory of knowledge, Popper's theory of these three "worlds" is also a cosmological theory. As is consistent with the known universe as presently described by the natural sciences, Popper maintains that the known universe did not contain any World 2 or World 3 from the outset - there was initially only a "World 1", a realm where everything consisted of physical states and processes. Moreover, that "World 1" was for a long time devoid of any living matter and so during that time lacked any biological level. The biological level is a level within World 1 that emerged from its physical-chemical evolution over a vast tract of time, as a lifeless universe eventually gave rise to living organisms, such as those on earth. In a similar sense to this emergence of life within World 1 itself, Popper maintains that a "World 2" of mental life later emerged as a product of biological evolution, and that subsequently "World 3" emerged as a product of evolution within the human "World 2".

This cosmological approach is directly opposed to any form of reductionism which claims that we can fully explain (and perhaps predict) whatever comes later in the known universe from the character of what came before or that we can always completely 'reduce' future characteristics of the universe to its past characteristics. Against such reductionist and deterministic views, Popper argues that we should view our universe as "creative" and indeterministic, especially in that it has given rise to genuinely new levels or realms - like biological life, "World 2" and "World 3" - that were not there from the beginning and which are not 'reducible' to what was there from the beginning.

The three worlds may be understood, within this evolutionary and cosmological framework, as containing three categories of entity:-

• World 1: the realm of states and processes as typically 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.

• 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. Mental states and processes only emerged as a product (or by-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.

• 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-motivated human action on World 1 - have an indirect but powerful affect 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.

Popper recognises that some form of World 1 and of World 2 is accepted by most people, but that his "World 3" goes beyond what is generally accepted as a matter of common sense. But the initial strangeness of World 3, in contrast to World 1 and World 2, may be counterbalanced by understanding that World 1 and World 2 are shown by science to be much stranger and more complex than they might appear to common sense, and shown even to defy common sense e.g. quantum physics within World 1 and perceptual illusions within World 2.

World 1 extends beyond what is testable by science to those aspects of physics, chemistry and biology that remain a matter of philosophical or metaphysical (i.e. untestable) conjecture - so, for example, arguments as to whether there exist any 'laws of physics' pertain to World 1 even though neither the existence nor non-existence of such laws can be tested (i.e. falsified) by observation (only forms of specified law can be falsified or tested, in Popper's view, not the general existence or non-existence of laws). Also pertaining to World 1 are untestable theories as to the origin of World 1 and the origin of life within it. Similarly, a proposition may pertain to World 2 or World 3 whether it is scientifically testable or not. Deeper than this, Popper does not claim our knowledge (whether scientific-testable or not) is, or ever could be, exhaustive of the reality it seeks to comprehend. His position is that even were we to reach apparent 'rock bottom' in our understanding of, say, the physical universe, we could never know for certain that we had reached the actual 'rock bottom'. Moreover, it may be that World 1 has aspects to its reality, including aspects fundamental to its physical nature, that we shall never understand - and perhaps that we are incapable of ever understanding. Equivalent points also hold true for World 2 and World 3.

To appreciate Popper's theory it helps to appreciate that:- (a) fundamental aspects of World 1 and World 2 defy "common sense" and might be regarded as extravagant and fantastical were they not shown by critical arguments, including experiments; (b) the reality of World 1 and World 2 are not themselves straightforwardly testable and their reality is better understood as a conjecture made as part of our metaphysical outlook; (c) we have not got to the bottom of understanding either World 1 or World 2; (d) we do not have any general theory of causation that explains the causal interactions within each realm and between each realm; (e) there are key aspects of human knowledge, including language acquisition and extending to scientific knowledge, that are difficult to explain in terms of subjective mental states and which are much better explained by a theory of World 3 and of "objective knowledge". Viewed in this wider perspective, World 3 may seem much less extravagant and fantastical as a metaphysical theory, and less vulnerable to the objections that it is not part of common sense and is not supported by a clear or testable explanation of how causally it may interact with World 2.

Among the many points and arguments Popper makes using his three worlds' schema, the following may be regarded as key claims regarding the role of World 3 in the known universe.

First, Popper argues that, notwithstanding 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 knowledge of World 3 objects.

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 a nuclear reactor is not the result of a purely World 1 process but is the product of a complex interaction between particular "World 3" theories and human "World 2" mental activity, and then particular human actions in "World 1" made possible by this complex interaction.

Third, Popper argues that one way to bring out the reality of World 3 is to consider how its existence drastically changes the state of World 1. He gives the contrasting examples of a disaster that wiped out civilisation including our stored knowledge (e.g. in libraries and in computers) and a similar disaster which left our stored knowledge substantially intact. In the first example, civilisation as we now know it, including its knowledge-base, would have to be rebuilt from scratch; whereas, in the second case, even if all the relevant experts had died in the disaster, we could avail of the stored knowledge-base to begin rebuilding. Popper argues that the stored knowledge-base is World 3 content in its physically encoded form - "World 3.1" - and its reality becomes clear when we consider how much more difficult the rebuilding of civilisation would likely be in the first example when contrasted with the second.

In contrast to the dominant Western tradition that identifies "knowledge" with special states within World 2 (e.g. with "justified true belief"), in Popper's theory of knowledge there exist forms of knowledge within World 1 as well as within World 2, and additionally there are knowable 'objects' within World 3. Popper's theory of knowledge is very different to the view that identifies knowledge with some form of "justified true belief", and he argues by contrast that:- (a) all knowledge is conjectural, and none is "justified" in the sense philosophers usually mean; (b) knowledge encompasses what is false as well as what is true e.g. Newton's physics, though strictly false, is highly significant knowledge - much more significant than knowledge that is true but trivial; (c) knowledge need not be believed, and the value of human knowledge stands in no strict correlation with our subjective degree of belief in it. According to Popper's views on knowledge:- (1) a tree may have knowledge, such as how to spread its roots to tap water; but this is biological knowledge within World 1 - a tree does not have mental states or World 2 knowledge; (2) in addition to such biological knowledge, explicable in World 1 terms, a dog may have mental states and World 2 knowledge - such as to when its owner is likely to return home; (3) only humans have knowledge that extends beyond World 1 and World 2 states and processes to knowledge of 'objects' or entities in the World 3 sense.

More on world 3

Popper's world 3 contains the products of thought. This includes abstract objects such as scientific theories, stories, myths and works of art. A world 3 object is something along the lines of a meta-object or a form of being. 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. It corresponds to the current state of our knowledge and culture.

The interaction of World 1 and World 2

Popper's theory of interaction between World 1 and World 2 provides an alternative to Cartesian dualism.

Popper's theory of the interaction of World 2 and World 3 may be said to provide a decisive step beyond mere mind-body dualism into a form of 'trialism', yet within that 'trialism' there is a distinctive theory of mind-body dualism. Notwithstanding Popper's World 3 'trialism', it is clear that Popper accepts that there was a time, before World 3 emerged, when there were only World 1 and World 2 entities - and therefore there was at that time only a mind-body dualism. Popper regards Descartes as correct in his recognition that we must take mind (or 'the mental') as being something crucially distinct from body (or 'the physical'), and in that sense Popper's position remains in the tradition of Descartes. But Popper considers that Descartes made two fundamental errors - first, in taking these distinct entities of mind and body to be constituted as "substances", and, second, in applying a restrictive theory of causation by 'push' to both the physical world and to the interaction of that physical world with 'mind'. In contrast to Descartes, Popper also allows that animals other that humans may have mental states and processes (e.g. dogs can be shown experimentally to have dream sleep); and Popper also allows for the existence of unconscious mental states and processes, and for differing degrees of conscious awareness in relation to mental states (e.g. an individual human may experience different degrees of conscious awareness in relation to their mental states in the course of the day, depending on factors like tiredness or whether they are in an emergency or are sleeping). Consequently, Popper's position is very different to that of Cartesian dualism and provides a form of dualism that is not vulnerable to the same criticisms.

Popper describes himself as a dualist in terms of mind and body, and he rejects any form of 'identity theory' whereby mental states are taken to be the same as physical brain states. Nevertheless his approach allows (1) for mental states to be in some sense dependent for their existence on a physical substrata in the brain; (2) for there to be close interconnectivity between mental states and physical brain states; (3) for many, if not most, mental states to be products of World 1 brain states and processes without in turn having any affect on any brain states or processes. Given this interconnectivity and interdependence between World 2 and the World 1 of brain activity, it is clear that when Popper speaks of the "autonomy" of World 2 from World 1 he does not mean complete autonomy in every respect - he means "autonomy" in certain specific instances of mental processing, so that the World 2 of the human mind may be regarded overall as having partial autonomy from its World 1 brain. In Popper's theory, this partial autonomy is then amplified by World 3:- because World 2 thought processes, which are autonomous from World 1, can create autonomous World 3 objects - and World 2's further interaction with those World 3 objects gives World 2 greater scope for the further pursuit of knowledge unbridled by the limitations of World 1 processes.

For Popper, dualism alone is not enough to grant the human mind any creative freedom or autonomy from its World 1 brain - for example, a mind-brain parallelism could be dualistic even if we lacked genuine mental freedom or rationality because our mental states were always mere epiphenomena to World 1 brain activity and so had no causal effect on World 1. It is in defence of human creativity, rationality and freedom that Popper stresses the 'causal openness' of World 1 to World 2 (and of World 2 to World 3) - that is, Popper's position is 'interactionist', not merely 'dualist'. Accordingly, it is a crucial part of Popper's view of World 1 and World 2 interaction that mental states can sometimes causally affect physical brain states i.e. mental states or processes can produce changes in World 1 brain states. For example, a human's deliberate conscious and rational action involves all of the following:- (a) a mental state (or process) that has some form of autonomy from World 1 brain states and processes, including those that may have helped produce it; (b) that mental state (or process) effecting changes to World 1 brain states; (c) the changed World 1 brain states producing World 1 action by the body. Popper argues that critical discussion favours the conclusion that there occurs such 'downward causation', i.e. of mental states/processes changing physical brain states/processes, even though we do not know how it occurs.

Popper argues that some form of mind-body dualist interaction has been the predominant position throughout human history, both philosophically and as a matter of common sense, and as reflected in the law. This dualism was taken as relatively unproblematic until the time of Descartes when it became a pressing concern to explain how something as possibly ethereal and scientifically untestable as 'mind' could fit within the materialistic and mechanistic conceptions of the Scientific Revolution. Popper proposes that mind-body dualism subsequently suffered because it became identified with "Cartesian dualism", which turns out to be an untenable form of dualist interactionism. In Descartes' approach, mind and body must interact by one 'pushing' on the other, as 'push' is the only form of causal connection accepted by Descartes. Yet in Descartes' view both mind and body are substances, the difference between them being that bodies are material substances and the mind consists of an immaterial substance. This proves untenable as a scheme of explanation because it is impossible to see how an immaterial substance (here 'mind') could 'push' on material bodies (say, the brain) when 'push' is conceived in a purely material way.

In opposition to this scheme of explanation, Popper rejects both the view that minds and bodies should be regarded as "substances" and Descartes' view that all causation is some form of 'push'. Popper also rejects those post-Cartesian theories that might appear to circumvent the causal issues, thrown up by interactionism, by denying there is any mind-body interaction - whether the denial takes the form of 'identity theories' that assert mental events are just physical brain events, or takes the form of a mind-body parallelism, such as epiphenomenalism, which denies mental activity has any effect on the physical world. More broadly, Popper also rejects a narrowly materialistic view of the universe, arguing that, since the Scientific Revolution, the programme of explaining everything in terms of matter has been transcended within science itself e.g. by the need to explain matter in terms of non-material forces. Popper's position is readily allied with the view that many intuitions and arguments (a) against the reality of an autonomous, causally affective World 2, and (b) for regarding World 1 as causally closed (i.e. as 'cut off' from World 2), are based on an outdated and overly simplistic view of the character of World 1.

Popper admits that we do not know how such different entities as mind and body could causally interact but argues this should not be regarded as an insuperable difficulty for dualist interactionism - for we do not know how it is possible for an invisible disembodied force like gravity to causally affect huge amounts of embodied matter like stars, but rightly do not regard this as an insuperable objection to a theory of gravitation. In short, we may know (or 'best guess') that certain different entities interact - even though in some fundamental sense we neither know how such interaction is possible nor know precisely how it may happen. We should also avoid prescribing that only a physical model of causality can apply when understanding mind-brain interaction - for we may know that a stock market crash will likely cause a rise in unemployment, or that a conductor dropping a baton may cause the orchestra to falter, while knowing that the model of this causality cannot be a matter of pure physics.

In Popper's version of dualist interactionism, human mental states and processes arise from extremely complex and intensely active World 1 processes in the brain. These World 1 activities may be analysed in terms of physics and chemistry but also biology, as the human brain is a living and highly active organ - the most complex and most intensely active entity within World 1. In many cases of mind-brain liaison, mental events may be mere causal upshots of World 1 brain processes, running parallel to the brain processes without affecting those processes in turn. But Popper argues that it does not fit with an evolutionary view of the mind to consider mental events as never producing any effect on the bodily brain:- for the evolution of greater mental capacity (that we may trace in the 'higher' animals compared to the 'lower') would have no rationale in terms of 'natural selection' if that greater mental capacity had no causal impact on the animal's actions and behaviour. Such evolution is very hard to rationally explain without recourse to 'natural selection' and it is very hard to apply 'natural selection' to the evolution of entities that play no causal role in survival and adaptive behaviour. Therefore there must exist instances of "downward causation", Popper argues, where some mental states or processes somehow sometimes act 'downwards' to alter brain states and thereby action and behaviour, if the evolution of human consciousness is to be understood as conferring any adaptive advantage in terms of 'natural selection'.

Popper's theory of World 3 allows him to take this last argument a step further, by regarding the development of World 3 as also conferring adaptive advantages, and with World 3's continued evolution being at least partly explained by the advantages conferred. Though the World 2 evaluation of World 3 objects is cultural rather than 'natural selection', there are, in Popper's view, many analogies to be drawn between cultural and natural evolution - especially that both work along the lines of non-inductive/Darwinian 'selection between variants' and not by inductive/Lamarckist 'instruction from environment'. The central adaptive advantage of human cultural evolution is that we can let our theories die in our stead, by having our knowledge advanced through non-violent intellectual competition. Human knowledge has advanced in depth and breadth beyond the knowledge attained by other animals, and this is bound up with the existence of World 3 and humans' World 2 access to it. The depth of our cognition and the scope of our error elimination exceeds that of other animals because we are able to articulate our knowledge as World 3 objects (e.g. theories) that have greater range and depth than what is otherwise presented by sensory or subjective experience in World 2, because we are able to investigate these World 3 constructs as "objective knowledge", and because we are able to subject them to much more rigorous and systematic testing and assessment than is otherwise possible with knowledge that merely exists in the form of subjective mental states.

So Popper's theory posits two cases of interaction - World 3 with World 2 and World 2 with World 1. In Popper's view both cases of interaction may be rationally defended even though in both cases we lack a theory of causation that adequately explains how this interaction occurs. Popper argues that, in truth, we lack such a theory of causation in general terms - even, specifically, for the interaction of different kinds of World 1 entity (e.g. the different physical forces with different particles; the effect of structures on their components and vice versa). The advances of science have shown our primitive views of World 1 causation (e.g. as materialistic 'push') to be highly inadequate (what we take as simple push between objects, like the hammer on the nail, is in fact mediated by force fields). But the myriad complexity of interactions within World 1, as revealed by science, is not underpinned by any general theory of causation or explanation of how those interactions are causally possible:- many fundamental interactions, such as forces with particles, are asserted as part of scientific theories but left further unexplained. Scientific theories generally present no testable explanation of how the theorised 'interactions' are causally possible in the sense under discussion e.g. a theory of the interaction of gravity and mass may posit a two-way relationship where gravity affects the behaviour of material mass and material mass affects the operation of gravity, without any testable explanation of how this two-way relationship is causally possible. In this light, Popper argues, we should not regard the absence of an explanation for how a form of interaction is causally possible as anything like a decisive argument against the existence of such interaction.

The interaction of world 2 and world 3

The interaction of world 2 and world 3 is based on the theory that world 3 is partially autonomous. For example, the development of scientific theories in world 3 leads to unintended consequences, in that problems and contradictions are discovered by world 2. Another example is that the process of learning causes world 3 to change world 2.

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 into an object of world 1 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.

See also

• Eccles' philosophy
• Platonic realm
• Third Realm (Frege)
• Trichotomy (philosophy)
• Group mind
• Logical Investigations

References

• Eccles, J. C. (1970). Facing Reality: Philosophical Adventures by a Brain Scientist. Springer Science & Business Media. ISBN 978-1-4757-3997-8.
• Heller, Michael (2011). Philosophy in Science: An Historical Introduction. Springer.
• 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.

Further reading

• Popper, Karl; Eccles, John C. (1977). The Self and Its Brain: An Argument for Interactionism.
• Popper, Karl (7 April 1978). Three Worlds by Karl Popper (PDF). The Tanner Lecture on Human Values. Talk delivered at The University of Michigan.
• Popper, Karl (1982). The Open Universe: An Argument for Indeterminism.
• Popper, Karl (1994). Knowledge and the Body-Mind Problem.
• Popper, Karl (1994) [First edition 1945]. The Open Society and Its Enemies. Routledge 2012, Princeton University Press 2013.{{cite book}}: CS1 maint: date and year (link)