Monism and Pluralism in Ontology.

Popper talks about the existence of physical reality (“World 1”), human minds (“World 2”) and our culture (“World 3”) as showing that material monism is incorrect (The Open Universe, vol. III of the Post Scriptum to The Logic of Scientific Discovery). Now, Popper says that it is clear that matter is real, when you interact with it, and that other minds are real when you interact with other people and they react to what you are saying or doing. Culture (World 3) has been created by Homo sapiens since the discovery of agriculture, cities, and the invention of the written language. But coming from Santayanaʼs ontology, I see that Popper does not discriminate between physicalism and broad naturalism.

Without a material world and a material brain you cannot have ideas, nor feelings, nor a culture. Hence, material monism, which is different from physicalism. A physicalist says that only material things exist. A naturalist says that only matter (and material brains) exist but from it arise many other immaterial things, like consciousness, feelings, sensations, perceptions, ideas, concepts, theories, etc.

So, if you take matter out there is nothing more which is able to be. Matter is the efficient base. It is the only existent thing. This is material monism. Now, from that material base (World 1) you have your material mind and other material minds (World 2) creating a culture (World 3). All are able to interact because there is a material, unified world: material nature. But what is the ontological category of a name, a thought, an idea, a feeling? Those are not material things. You do not see a C major chord walking down the street. You feel it when you listen to it in your mind. The idea of a C major chord is an essence. It is that character you feel in your mind but cannot hold materially, as it does not exist, but is.

Naturalism means that mind is part of nature. That mind is not separated from nature, that it is not something supernatural or divine. It is a material brain with many modules created through evolution by natural (and sexual an kin) selection. Dualism or pluralism is not anymore a good perspective to see human minds and human culture, as Evolutionary Psychology shows today. All human conduct and all human artifacts are biological phenomena, created by our interaction with our material environment. 

Popper calls World 3 real. Indeed, it is. The reality is what we create with those ideas and theories. The ideas themselves are real, but non-existent. Have you seen a theory created by a human mind living by itself in the material world? You have not. And will not. Because the theory is entirely non-existent, immaterial. You need a material brain to see its meaning. It is when you apply your ideas to change the world that a material thing is created: a rocket, a computer, a house. Richard Dawkins called culture our extended phenotype over the world, what Popper calls World 3. There is no plurality here: it is monism as to the material reality and our material brains. The ideas and feelings, instincts and adaptations, perceptions and sensations we have come when we have a material brain, which in action turns into a mind. If it could be proved that minds live without a material base, then we would have dualism, or pluralism. As it is today, nature is one unified system, and all culture is part of it. There is no dualism. The question is not nature or nurture. The question is nature and culture. Biology. Which is what Evolutionary Psychology today studies and has not been falsified yet. 

In The Adapted Mind (Oxford University Press, eds. Barkow, Cosmides, and Tooby, 1995, pp. 21-22) we read about this monism:

With the appearance of Darwinism, the full scope of the emerging unified account was, for the first time, apparent. Therefore, much of the opposition has specifically revolved around evolution and its application to humans. Gladstone, for example, in a debate with Huxley, captured in his choice of language the widely shared, visceral sense of revulsion caused by the claim “that natural selection and the survival of the fittest, all in the physical order, exhibit to us the great arcanum of creation, the sun and the center of life, so that mind and spirit are dethroned from their old supremacy, are no longer sovereign by right, but may find somewhere by charity a place assigned them, as appendages, perhaps only as excrescences, of the material creation” (Gladstone, quoted in Gould, 1988, p. 14). The dislocations in world view stemming from this process of conceptual unification led to a growing demand for, and production of, conceptual devices and rationales to divorce the natural sciences from the human social and inner landscape, to blunt the implications of monism and Darwinism, and to restore a comfortable distance between the human sciences and the world of natural causation. To many scholarly communities, conceptual unification became an enemy, and the relevance of other fields a menace to their freedom to interpret human reality in any way they chose.

Naturalism does not mean that only matter is real. Naturalism means that only matter is existent, and efficient. You may contemplate essences in your mind as long as you want, but only your physical action will change the world. It is through material action, physical action, that we interact with the world, that we survive and reproduce. Thanks to culture (World 3) and minds (World 2) we are better adapted to the environment (World 1). There is no plurality here. It is the same unified field of action. Nature. Monism. The material world. Remove the existent World 1 and the non-existent reality of essences and spirit (consciousness) disappears.