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Biological naturalism is a monist theory about the relationship between mind and body (i.e. brain), and hence an approach to the mind-body problem. It was first proposed by the philosopher John Searle in 1980 and is defined by two main theses: 1) all mental phenomena from pains, tickles, and itches to the most abstruse thoughts are caused by lower-level neurobiological processes in the brain; and 2) mental phenomena are higher level features of the brain.
These theses imply that conscious states and intentionality can be reduced to natural brain processes -- they are caused by and realized in the brain. This entails that the brain has the right causal powers to produce intentionality. However, it should be noted that Searle's biological naturalism does not entail that brains and only brains can cause consciousness. Searle is careful to point out that while it appears to be the case that certain brain functions are sufficient for producing conscious states, our current state of neurobiological knowledge prevents us from concluding that they are necessary for producing consciousness.
Searle denies Cartesian dualism, the idea that the mind is a separate kind of substance to the body, as this contradicts our entire understanding of physics, and unlike Descartes, he does not bring God into the problem. Indeed, Searle denies any kind of dualism, the traditional alternative to monism, claiming the distinction is a mistake. He rejects the idea that because the mind is not objectively viewable, then it does not comprise part of physics.
Searle believes that consciousness "is a real part of the real world and it cannot be eliminated in favor of, or reduced to, something else" whether that something else is a neurological state of the brain or a software program. He contends, for example, that the software known as Deep Blue knows nothing about chess. He also believes that consciousness is both a cause of events in the body and a response to events in the body.
On the other hand, Searle doesn't treat consciousness as a ghost in the machine. He treats it, rather, as an emergent property of the brain as a whole (See holism). The causal interaction of mind and brain can be described thus in naturalistic terms: Events at the micro-level (perhaps at that of individual neurons) cause consciousness. Changes at the macro-level (the whole brain) constitute consciousness. Micro-changes cause and then are impacted by holistic changes, in much the same way that individual football players cause a team (as a whole) to win games, causing the individuals to gain confidence from the knowledge that they are part of a winning team.
The theory is sometimes mistakenly viewed as a kind of property dualism, since, in Searle's view, a person's mental properties are categorically different from his or her micro-physical properties. The latter have "third-person ontology" whereas the former have "first-person ontology." Micro-structure is accessible objectively by any number of people, as when several brain surgeons inspect a patient's cerebral hemispheres. But pain or desire or belief are accessible subjectively by the person who has the pain or desire or belief, and no one else has that mode of access. However, Searle understands mental properties to be a species of physical property -- ones with first-person ontology. So this sets his view apart from a dualism of physical and non-physical properties. His mental properties are putatively physical.
There have been several important criticisms of Searle's idea of biological naturalism. Jerry Fodor suggests that Searle gives us no account at all of exactly why he believes that a biochemistry like, or similar to, that of the human brain is indispensable for intentionality. It seems much more plausible to suppose, Fodor thinks, that it is the way in which an organism (or any other system for that matter) is connected to its environment that is indispensable in the explanation of intentionality. It is easier to see how the fact that my thought about a desk is causally related with a desk can bear on the fact that my thought is about a desk than it is to see how the fact that my thought is made up of hydrocarbons can bear on the fact that my thought about a desk is about a desk.
John Haugeland takes on the central notion of some set of special "right causal powers" that Searle attributes to the biochemistry of the human brain. He asks us to imagine a concrete situation in which the "right" causal powers are those that our neurons have to reciprically stimulate one another. In this case, silicon-based alien life forms can be intelligent just in case they have these "right" causal powers; i.e they possess neurons with synaptics connetions that have the power to reciprocally stimulate each other. Then we can take any speaker of the Chinese langauge and cover his neurons in some sort of wrapper which prevents them from being influenced by neurotransmitters and, hence, from having the right causal powers. At this point, "Searle's demon" (an English speaking nanobot, perhaps) sees what is happening and intervenes: he sees through the covering and determines which neurons would have been stimulated and which not and proceeds to stimulate the appropriate neurons and shut down the others himself.
The experimental subject's behavior is unaffected. He continues to speak perfect Chinese as before the operation but now the causal powers of his neurotransmietters have been replaced by someone who does not understand the Chinese language. The point is generalizable: for any causal powers, it will always be possible to hypothetcially replace them with some sort of Searlian demon which will carry out the operations mechanically. The conclusion is that Searle's is necessarily a dualistic view of the nature of causal powers, "not intrinsically connected with the actual powers of physical objects."
- John R. Searle, Biological Naturalism.
- John R. Searle, The Mystery of Consciousness (London: Granta Publications, 1998).
- John R. Searle, The Rediscovery of the Mind (Massachusetts: MIT Press, 1994).
- John R. Searle, Mind: A Brief Introduction (New York: Oxford University Press, 2004).
- Fodor, Jerry. (1980) "Searle On What Only Brains Can Do". Behavioral and Brain Sciences. vol. 3. pp.217-219
- Haugeland, John. (1980) "Artifical Intelligence". Behavioral and Brain Sciences. vol. 3. pp. 219-224.
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