Poppers criticism of materialism

In his famous book written with J. C. Eccles and published in 1977, The Self and Its Brain (Popper & Eccles 1985, 2nd ed.), and in other subsequent essays (see especially Popper 1994) Popper proposes a theory of the mind that aspires to be both naturalistic and anti-materialistic. This theory can be so summarised:

1. Life emerged from matter, consciousness from life, and "objective knowledge" (especially scientific theories) from human consciousness (Popper & Eccles 1985:11). Popper calls the physical and biological world "World 1", the set of all mental states "World 2", and the set of all cultural products of human intelligence - from myths to works of art, scientific theories, other abstract objects, and social institutions - "World 3". Given these definitions he maintains that the second world emerged from the first world and the third world from the second world. In other words, life is the result of physical and chemical processes, consciousness (that Popper seems to identify with 'mentality' at large in an Cartesian vein) emerged from life at a certain point of the evolution of species, and only through the intelligent activity of human beings, that is, by repeated mental acts, all products of human culture were brought about. Therefore, there is no life without matter, no minds without brains, and no culture without human minds (Popper & Eccles 1985:36-39). More in detail, as for the 'mind-body problem' Popper, unlike Eccles, does not believe in "the existence of disembodied minds" (206). Therefore it seems reasonable to conclude that Popper, unlike Descartes, does not believe in the possibility of mental states without any brain correlates and maintains that the 'higher levels' of reality have been produced by lower levels: life from matter, minds from organisms etc. There is a causal relation from lower levels to higher levels.

2. There is not only a causal relation from lower levels to higher levels but also vice versa a 'backward' causal relation from higher levels to lower levels. For example, scientific theories have deeply changed the physical world through their technological applications. Moreover, since science cannot act directly on the physical world such an interaction between the abstract objects of the World 3 and the material objects of the World 1 needs the mediation of the World 2, that is, the mediation of human beings. Therefore there are backward causal relations from the World 3 to the World 2 and from the World 2 to the World 1. For example, through mental processes human beings have conceived scientific theories and devised technological applications that have deeply modified the physical world (Popper & Eccles 1985:47-48). As for the mind-body problem, this means that mental acts can have effects on the physical world. For example, if you go to a dentist's because you have a toothache "the caries in your tooth - a material, physico-chemical process - will thus lead to physical effects [the movements of your legs in order to go to the dentist's etc.]; but it does so by way of your painful sensations, and of your knowledge of existing institutions, such as dentistry" (Popper & Eccles 1985:36).

3. Only two 'things'8 that are ontologically distinct can be connected by a relation between cause and effect. Since minds can cause physical events in bodies, and abstract objects of the World 3 can cause mental acts in the minds of human beings, minds and abstract objects are real: "Besides the physical objects and states, I conjecture that there are mental states, and that these states are real since they interact with our bodies" (Popper & Eccles 1985:36; Popper's italics). In other words, the existence of mental causation is an empirical proof that the mind is an autonomous emergent level of reality. Materialists, denying the existence of minds as an emergent level of reality distinct from matter, cannot explain how mental acts can be the cause of anything. Only 'things' that have an autonomous existence can be the cause of something. Therefore, if materialism were true no backward causation of the mental on the physical would be possible. However, such a mental causation exists, thus materialism is false (Popper & Eccles 1985:14ff.).

4. A materialist could object that, if backward mental causation really implied a violation of the closure of the physical world, then one should reject mental causation since the closure of the physical world is a well established law of physics. However, Popper replies to such an objection that the closure of the physical world, far from being a well established natural law, "is clearly refuted by the technical, scientific, and artistic achievements of mankind", that is, the creativity of mankind proves that the universe is open to novelties (Popper & Eccles 1985:207). 5. The only dualistic theory of mind that can be compatible with the closure of the physical world is epiphenomenalism: consciousness emerged from a biological basis but cannot react on it. However, epiphenomenal-ism is an implausible theory since to explain how consciousness emerged from matter in the course of biological evolution is very difficult if one claims that consciousness has no causal efficacy on the physical world and is completely useless for animals in their struggle for life (Popper & Eccles 1985:74).

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