Popper's Three Worlds

The concept involves three interacting worlds, called world 1, world 2 and world 3.

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

Their numbering reflects their temporal order within the known universe and the fact the later realms emerged as products of developments within the preceding realms.

Popper's theory of these three "worlds" is crucially 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 at its inception - at its inception there was only a "World 1", a realm where everything consisted of physical states and processes. Moreover, that "World 1" was for a very long time devoid of any living matter and so was for a very long time a World 1 lacking 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 "World 2" 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 strongly opposed to any form of reductionism that might suggest we can ultimately explain whatever comes later in the known universe from what came before - against this, Popper argues that we should see the universe as creative and indeterministic 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, in this evolutionary and cosmological sense, 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.
• 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 emerge subsequent to the emergence of living organisms within World 1.
• 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.

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. 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 we can only understand the existence of a nuclear reactor by understanding it is in reality 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 World 1 actions by humans arising from this complex interaction.

Popper's world 3 contains the products of thought. This includes abstract objects such as scientific theories, stories, myths and works of art. Popper says that his world 3 has much in common with Plato's theory of Forms or Ideas. 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 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.

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 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 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.

• Collective consciousness
• Eccles' philosophy
• George Berkley
• Subjective idealism
• Four worlds
• Logical Investigations
• Platonic realm
• Third Realm (Frege)
• Trichotomy (philosophy)

• 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 (1994b). Knowledge and the Body-Mind Problem.
• Popper, Karl (1994c) [1945]. The Open Society and Its Enemies. Routledge 2012, Princeton University Press 2013.