One of the main claims of physicalism reads that the physical world is a closed system which cannot be affected by anything external to it. This has important consequences for the causal efficacy of consciousness and the mind in general. Basically, physicalism for reality as a whole states that nothing is ever caused by any non-physical factor. If there is a mind it has to be something physical or else it cannot be causally efficacious. Now, within this system, there are three viable options :
- There is no non-physical mind, meaning that mind is either an outdated category (eliminative materialism) or can be reduced to neurological processes (reductive materialism).
- There is a non-physical mind, but only from a subjective point of view. Objectively speaking only brain processes are real (identity theory).
- There is a non-physical mind, but it is not causally efficacious (epiphenomenalism).
As Hein van Dongen and I have shown elsewhere, of these options only the first is logically tenable. As soon as we acknowledge the existence of subjective awareness as such, we also have to accept that subjective awareness has had a causal impact on our cognition. Without such a causal impact there could be no reason anymore to believe in subjective experiences, as they would become completely unknowable in the sense that we could not form any concepts of them based on any type of impression they have made on our cognitive processes. In other words, accepting a non-physical mind or consciousness and denying its causal efficay creates a major contradiction, meaning that (at least) one of these concepts (either the existence of consciousness or its non-efficacy) must be rejected.
Now, some scholars do in fact accept that consciousness must be causally efficacious because otherwise it would not be able to affect our cognitive apparatus in the mental sense and could never lead to a realistic concept of consciousness. However, they do not accept that consciousness also affects the physical world. This position is mainly formulated as parallellism, meaning that for every psychogenic process in the mind there is a corresponding somatogenic physical process somewhere in the brain, but neither process affects its counterpart.
Elsewhere, I have already shown that the denial of a psychogenic impact on the physical world leads to two contradictions:
The denial of psychogenic physical processes implies it is impossible that physically spoken or written words refer to subjective experiences as such, because there is no causal connection anymore between physically expressed words and the realm of the subjective. The reason why this is contradictory, is that parallellism implicitly claims it can enter the philosophical debate via spoken and written words. If its physically expressed words cannot directly refer to consciousness it should remain silent (being a position about consciousness, as well as about the physical world, and causality), i.e. disqualify itself within the public domain.
Secondly, according to parallellism the mind can contain no representations that would have causally originated in the physical world. This means that we could have no reason to believe in a physical world because our concepts of such a realm could never be based on any type of impact of it on our minds.
Here I would like to add a similar analytical argument. If parallellism is true there must be a specific 'computational' counterpart in the brain for any type of mental process. This counterpart must be part of a completely autonomous causal chain, i.e. it must have been caused by physical, non-mental causes alone. If so, there must be a specific physical counterpart for any concept in the mind and another, non-identical and specific physical counterpart for the concept (in the mind) of a physical counterpart of the concept in the mind.
However, this is logically impossible. Even if there were a specific physical counterpart for a concept in the mind, the brain would have no physical 'reason' to make a distinction between its physical counterpart of the mental concept and the mental concept as such. For the mind, a mental concept and a physical 'concept' are not identical, but there can be no physical parallel of this distinction. There is no way to physically distinguish the one from the other, whereas from a mental perspective the mental concept and its proposed physical counterpart would differ ontologically. The distinction in the mind is based on a notion of physical, non-mental processes, whereas there can be no such distinction in the brain between its own physical processes and non-physical consciousness. Perhaps a parallellist could - falsely according to his own position as we have seen above - claim he infers there is a physical world from his mental impressions, but he would never claim the brain infers there is a non-physical mind, as the brain would certainly lack any information about consciousness (and the other way around, but this is as said overlooked much more often by many parallellists).
The same would go for any conceptual distinction between a mental entity and a possible physical counterpart of it. Within the processing of the mind there would be a reason to make such distinctions, and within computational processing in the brain there would not. So no parallel process could be taking place neurophysiologically whenever the mind makes a conceptual dinstinction between one of its own mental processes, structures or subjective experiences and physical processes, structures or non-subjective events in the brain. I'm not saying that there would usually be no brain activity whatsoever whenever the mind makes such a distinction. I'm just saying that the brain activity cannot be a precise, computational match of the mental processing, i.e. it cannot amount to a computational counterpart of the distinction (in the mind) between mental and physical entities. If the brain processes play any role during mental processing of the distinction between mental and physical entities, it must be an interactive role, led by the mind. As in dualist interactionism.
In other words, for parallellism consciousness and the physical world are supposed to be different. The mind dinstinguishes between both of them because it is familiar with its own consciousness and it deduces mathematical, spatial and temporal properties of matter from its own subjective impressions. The brain knows no such distinction (between a non-physical mind and a physical world), because it lacks any impressions of consciousness whatsoever. The brain has no information by which it could distinguish between phenomenal consciousness and a physical world. Therefore, it is completely impossible that it would make such a distinction, let alone autonomously and without any impact caused by consciousness.
Once more, the foregoing implies that parallellism is a contradictory position.
What needs to be abandoned more than anything from an analytical standpoint is the inconsistent, logically untenable notion of a closed physical universe that could not be affected by non-physical entities. Unless, that is, one would really wish to abandon the notion of subjective awareness, which is obviously quite an absurd position if we judge it from an empirical (introspective) perspective.
Nijmegen, December 2006