Physicalism

In philosophy, physicalism is the view that "everything is physical", that there is "nothing over and above" the physical, or that everything supervenes on the physical. It is opposed to idealism, according to which the world arises from mind. Physicalism is a form of ontological monism—a "one substance" view of the nature of reality, unlike "two-substance" (mind–body dualism) or "many-substance" (pluralism) views. Both the definition of "physical" and the meaning of physicalism have been debated.

Physicalism is closely related to materialism, and has evolved from materialism with advancements in the physical sciences in explaining observed phenomena. The terms "physicalism" and "materialism" are often used interchangeably, but can be distinguished on the basis that physics describes more than just matter. Physicalism encompasses matter, but also energy, physical laws, space, time, structure, physical processes, information, state, and forces, among other things, as described by physics and other sciences, all within a monistic framework.

According to a 2020 survey, physicalism is the majority view among philosophers at 51.9%, while there also remains significant opposition to physicalism.

Outside of philosophy, physicalism can also refer to the preference or viewpoint that physics should be considered the best and only way to render truth about the world or reality.

Definition of physicalism in philosophy

The word "physicalism" was introduced into philosophy in the 1930s by Otto Neurath and Rudolf Carnap.

The use of "physical" in physicalism is a philosophical concept and can be distinguished from alternative definitions found in the literature (e.g., Karl Popper defined a physical proposition as one that can at least in theory be denied by observation). A "physical property", in this context, may be a metaphysical or logical combination of properties which are not physical in the ordinary sense. It is common to express the notion of "metaphysical or logical combination of properties" using the notion of supervenience. Supervenience is the idea that there cannot be two events alike in all physical respects but differing in some mental respect, or that an object cannot alter in some mental respect without altering in some physical respect. The reason to introduce supervenience is that physicalists usually suppose the existence of various abstract concepts that are non-physical in the ordinary sense of the word.

Token physicalism

See also: Anomalous monism

Token physicalism is the proposition that for every actual particular (object, event or process) x, there is some physical particular y such that x = y. Token physicalism is compatible with property dualism, in which all substances are "physical" but physical objects may have mental properties as well as physical ones. But token physicalism is not equivalent to supervenience physicalism. First, token physicalism does not imply supervenience physicalism because the former does not rule out the possibility of non-supervenient properties (provided that they are associated only with physical particulars).

Reductionism and emergentism

Reductionism

There are multiple versions of reductionism. In the context of physicalism, reductions are of a "linguistic" nature, allowing discussions of, say, mental phenomena to be translated into discussions of physics. In one formulation, every concept is analyzed in terms of a physical concept. One counterargument to this supposes there may be an additional class of expressions that is non-physical but increases a theory's expressive power. Another version of reductionism is based on the requirement that one theory (mental or physical) be logically derivable from a second.

The combination of reductionism and physicalism is usually called "reductive physicalism", and the opposite view "non-reductive physicalism". Reductive physicalism is the view that mental states are nothing over and above physical states and reducible to physical states. One version of reductive physicalism is type physicalism, or mind-body identity theory. Type physicalism asserts that "for every actually instantiated property F, there is some physical property G such that F=G". Unlike token physicalism, type physicalism entails supervenience physicalism.

Another common argument against type physicalism is multiple realizability, the possibility that a psychological process (say) could be instantiated by many different neurological processes (or non-neurological processes, in the case of machine or alien intelligence). In this case, the neurological terms translating a psychological term must be disjunctions over the possible instantiations, and it is argued that no physical law can use these disjunctions as terms. Type physicalism was the original target of the multiple realizability argument, and it is not clear that token physicalism is susceptible to objections from multiple realizability.

Emergentism

Main article: Emergentism

There are two versions of emergentism, the strong and weak versions. Supervenience physicalism has been seen as a strong version of emergentism, in which a subject's psychological experience is considered genuinely novel. Non-reductive physicalism, on the other side, is a weak version of emergentism because it does not require that a subject's psychological experience be novel. The strong version of emergentism is incompatible with physicalism. Since there are novel mental states, mental states are not nothing over and above physical states. But the weak version of emergentism is compatible with physicalism.

Emergentism is a very broad view. Some forms of it appear either incompatible with physicalism or equivalent to it (e.g. posteriori physicalism); others appear to merge both dualism and supervenience. Emergentism compatible with dualism claims that mental states and physical states are metaphysically distinct while maintaining the supervenience of mental states on physical states. But this contradicts supervenience physicalism, which denies dualism.

A priori versus a posteriori physicalism

Physicalists hold that physicalism is true. A natural question for physicalists, then, is whether the truth of physicalism is deducible a priori from the nature of the physical world (i.e., the inference is justified independently of experience, even though the nature of the physical world can itself only be determined through experience) or can only be deduced a posteriori (i.e., the justification of the inference itself is dependent upon experience). So-called "a priori physicalists" hold that from knowledge of the conjunction of all physical truths, a totality or that's-all truth (to rule out non-physical epiphenomena, and enforce the closure of the physical world), and some primitive indexical truths such as "I am A" and "now is B", the truth of physicalism is knowable a priori. Let "P" stand for the conjunction of all physical truths and laws, "T" for a that's-all truth, "I" for the indexical "centering" truths, and "N" for any [presumably non-physical] truth at the actual world. We can then, using the material conditional "→", represent a priori physicalism as the thesis that PTI → N is knowable a priori. An important wrinkle here is that the concepts in N must be possessed non-deferentially in order for PTI → N to be knowable a priori. The suggestion, then, is that possession of the concepts in the consequent, plus the empirical information in the antecedent is sufficient for the consequent to be knowable a priori.

An "a posteriori physicalist", on the other hand, will reject the claim that PTI → N is knowable a priori. Rather, they would hold that the inference from PTI to N is justified by metaphysical considerations that in turn can be derived from experience. So the claim then is that "PTI and not N" is metaphysically impossible.

One commonly issued challenge to a priori physicalism and to physicalism in general is the "conceivability argument", or zombie argument. At a rough approximation, the conceivability argument runs as follows:

P1) PTI and not Q (where "Q" stands for the conjunction of all truths about consciousness, or some "generic" truth about someone being "phenomenally" conscious [i.e., there is "something it is like" to be a person x] ) is conceivable (i.e., it is not knowable a priori that PTI and not Q is false).

P2) If PTI and not Q is conceivable, then PTI and not Q is metaphysically possible.

P3) If PTI and not Q is metaphysically possible then physicalism is false.

C) Physicalism is false.

Here proposition P3 is a direct application of the supervenience of consciousness, and hence of any supervenience-based version of physicalism: If PTI and not Q is possible, there is some possible world where it is true. This world differs from [the relevant indexing on] our world, where PTIQ is true. But the other world is a minimal physical duplicate of our world, because PT is true there. So there is a possible world which is a minimal physical duplicate of our world, but not a full duplicate; this contradicts the definition of physicalism that we saw above.

Since a priori physicalists hold that PTI → N is a priori, they are committed to denying P1) of the conceivability argument. The a priori physicalist, then, must argue that PTI and not Q, on ideal rational reflection, is incoherent or contradictory.

A posteriori physicalists, on the other hand, generally accept P1) but deny P2)--the move from "conceivability to metaphysical possibility". Some a posteriori physicalists think that unlike the possession of most, if not all other empirical concepts, the possession of consciousness has the special property that the presence of PTI and the absence of consciousness will be conceivable—even though, according to them, it is knowable a posteriori that PTI and not Q is not metaphysically possible. These a posteriori physicalists endorse some version of what Daniel Stoljar (2005) has called "the phenomenal concept strategy". Roughly speaking, the phenomenal concept strategy is a label for those a posteriori physicalists who attempt to show that it is only the concept of consciousness—not the property—that is in some way "special" or sui generis. Other a posteriori physicalists eschew the phenomenal concept strategy, and argue that even ordinary macroscopic truths such as "water covers 60% of the earth's surface" are not knowable a priori from PTI and a non-deferential grasp of the concepts "water" and "earth" et cetera. If this is correct, then we should (arguably) conclude that conceivability does not entail metaphysical possibility, and P2) of the conceivability argument against physicalism is false.

Criticism and Arguments Against Physicalism

Knowledge argument

Though there have been many objections to physicalism throughout its history, many of these arguments concern themselves with the apparent contradiction of the existence of qualia in an entirely physical world. The most popular argument of this kind is the so-called knowledge argument as formulated by Frank Jackson, titled Mary's room.

The argument asks us to consider Mary, a young girl who has been forced to investigate the world from a black and white room via a black and white television monitor throughout her life. However, she is allowed access to a large number of books, containing all physical knowledge within them. During her time in the room, she eventually comes to know all of the physical facts about the world, including all of the physical facts about color. Now, to the physicalist, it would seem that this would entail Mary knowing everything about the world. However, once she is let out of her room and into the world, it becomes apparent that Mary does not know everything about the world, such as the feeling or experience of seeing color. If Mary did not have such knowledge, how can it be said that everything supervenes upon the physical?

Physicalist Response

One way the physicalist may respond to this argument is through the ability hypothesis, developed by Lawrence Nemerow and David Lewis. The ability hypothesis draws a distinction between propositional knowledge, such as 'Mary knows that the sky is typically blue during the day', and knowledge-how, such as 'Mary knows how to climb a mountain'. It then states that all that Mary gains from her experience is knowledge-how. This argument shows that while Mary does gain knowledge from her experience, it is not the propositional knowledge which would need to be obtained if the knowledge argument were to be logically sound .

Perhaps one could argue that the circumstances of Mary's room do not include all physical knowledge because it does not include particular wavelengths of light. In other words, for Mary to have the feeling or experience of seeing color, she must be exposed to color. Then because color is a wavelength of light, it too is physical knowledge, and thus must be included in the books that Mary has. She would therefore be exposed to these wavelengths of light while still in the room, and would thus have the feeling or experience of seeing color.

Argument from philosophical zombies

The zombie argument is a thought experiment that states "there is a possible world in which there exist zombies". Zombies are organisms that appear to have consciousness and qualia, but in reality do not. Also, in this case the zombies have to be identical copies of organisms in the actual or other possible world.

It has been argued under physicalism, that one must either believe that anyone including oneself might be a zombie, or that no one can be a zombie - following from the assertion that one's own conviction about being (or not being) a zombie is a product of the physical world and is therefore no different from anyone else's. This argument has been expressed by Dennett who argues that "Zimboes think^Z they are conscious, think^Z they have qualia, think^Z they suffer pains - they are just 'wrong' (according to this lamentable tradition), in ways that neither they nor we could ever discover!"

The possibility of zombies would also entail that mental states do not supervene upon physical states, a claim that the physicalist is committed to, and Australian Philosopher David Chalmers argues that the coherent conceivability of a zombie entails a metaphysical possibility. It has also been explained by arguing that the zombie argument rests on the concept of the nature of qualia. If certain non-physical properties exist which match our conception of qualia, then such non-physical properties would be qualia, and zombies would be conceivable and metaphysically possible. However, if there are no non-physical properties, then what we think of as qualia are the physical properties which perform the functional tasks of what we conceive of as qualia. In this scenario, zombies would not be metaphysically possible.

Physicalist Response

Although it has been argued that zombies in an observed world are indistinguishable from the observer (and therefore non-existent) under the assumption of physicalism, it has also been argued that zombies are not conceivable. It has been claimed under reductive physicalism, that when a distinction is made in ones mind between a hypothetical zombie and oneself (assumed not to be a zombie), and noting that the concept of oneself under reductive physicalism may ever only correspond to physical reality, the concept of the hypothetical zombie can only be a subset of the concept of oneself and will in this nature also entail a deficit in observables (cognitive systems) thereby contradicting the original definition of a zombie. This argument has been expressed by Daniel Dennett who argues that, "when philosophers claim that zombies are conceivable, they invariably underestimate the task of conception (or imagination), and end up imagining something that violates their own definition". Dennett, in The Unimagined Preposterousness of Zombies (1995) compares consciousness to health.

Supposing that by an act of stipulative imagination you can remove consciousness while leaving all cognitive systems intact — a quite standard but entirely bogus feat of imagination — is like supposing that by an act of stipulative imagination, you can remove health while leaving all bodily functions and powers intact. … Health isn't that sort of thing, and neither is consciousness.

Hempel's Dilemma

Main article: Hempel's Dilemma

Physicalists have traditionally opted for a "theory-based" characterization of the physical either in terms of current physics or a future (ideal) physics. Hempel's Dilemma (named after the philosopher of science Carl Gustav Hempel) attacks how physicalism is defined. Very roughly, Hempel's dilemma is that if we define the physical by reference to current physics, then physicalism is very likely to be false, as it is very likely (by pessimistic meta-induction) that much of current physics is false. But if we instead define the physical in terms of a future (ideal) or completed physics, then physicalism is hopelessly vague or indeterminate.

Physicalist Response

While the force of Hempel's dilemma against theory-based conceptions of the physical remains contested, alternative "non-theory-based" conceptions of the physical have also been proposed. Frank Jackson, for example, has argued in favour an "object-based" conception of the physical.

David Papineau and Barbara Montero have advanced and defended a "via negativa" characterization of the physical. The gist of the via negativa strategy is to understand the physical in terms of what it is not: the mental. In other words, the via negativa strategy understands the physical as the non-mental.

Andre Melnyk and like-minded physicalists accept the first horn of the dilemma. That is, a physicalists a physicalist can live with the idea that the current definition of physicalism may very likely end up being false as longs as they believe the proposition is more plausible than any currently formulated rival proposition, such as dualism. Melnyk maintains that this is precisely the attitude most scientist hold towards current scientific theories anyway. For example, a defender of evolution may well accept that the current formulation of evolutionary theory is likely to be revised in the future, but she defends evolution because she believes current evolutionary theory is more likely than any current rival idea, such as Creationism. Thus, Melnyk's is that one should define physicalism in relation to current physics, and hold a similar attitude towards its truth as most scientists hold towards the truth of currently accepted scientific theories.

Jaegwon Kim's argument against non-reductivism

Figure demonstration how M1 and M2 are not reduced to P1 and P2.

In response to Davidson's anomalous monism, Kim proposed that one cannot be a physicalist and a non-reductivist. He proposes (using the chart on the right) that M1 causes M2 (these are mental events) and P1 causes P2 (these are physical events). P1 realises M1 and P2 realises M2. However M1 does not causally effect P1 (i.e., M1 is a consequent event of P1). If P1 causes P2, and M1 is a result of P1, then M2 is a result of P2. He says that the only alternatives to this problem is to accept dualism (where the mental events are independent of the physical events) or eliminativism (where the mental events do not exist).

Other views

Realistic physicalism

Galen Strawson's realistic physicalism or realistic monism entails panpsychism – or at least micropsychism. Strawson argues that "many—perhaps most—of those who call themselves physicalists or materialists [are mistakenly] committed to the thesis that physical stuff is, in itself, in its fundamental nature, something wholly and utterly non-experiential... even when they are prepared to admit with Eddington that physical stuff has, in itself, 'a nature capable of manifesting itself as mental activity', i.e. as experience or consciousness". Because experiential phenomena allegedly cannot be emergent from wholly non-experiential phenomena, philosophers are driven to substance dualism, property dualism, eliminative materialism and "all other crazy attempts at wholesale mental-to-non-mental reduction".

Real physicalists must accept that at least some ultimates are intrinsically experience-involving. They must at least embrace micropsychism. Given that everything concrete is physical, and that everything physical is constituted out of physical ultimates, and that experience is part of concrete reality, it seems the only reasonable position, more than just an 'inference to the best explanation'... Micropsychism is not yet panpsychism, for as things stand realistic physicalists can conjecture that only some types of ultimates are intrinsically experiential. But they must allow that panpsychism may be true, and the big step has already been taken with micropsychism, the admission that at least some ultimates must be experiential. 'And were the inmost essence of things laid open to us' I think that the idea that some but not all physical ultimates are experiential would look like the idea that some but not all physical ultimates are spatio-temporal (on the assumption that spacetime is indeed a fundamental feature of reality). I would bet a lot against there being such radical heterogeneity at the very bottom of things. In fact (to disagree with my earlier self) it is hard to see why this view would not count as a form of dualism... So now I can say that physicalism, i.e. real physicalism, entails panexperientialism or panpsychism. All physical stuff is energy, in one form or another, and all energy, I trow, is an experience-involving phenomenon. This sounded crazy to me for a long time, but I am quite used to it, now that I know that there is no alternative short of 'substance dualism'... Real physicalism, realistic physicalism, entails panpsychism, and whatever problems are raised by this fact are problems a real physicalist must face.

— Galen Strawson, Consciousness and Its Place in Nature: Does Physicalism Entail Panpsychism?

Christian List argues that Benj Hellie's vertiginous question, i.e. why a given individual exists as that individual and not as someone else, and the existence of first-personal facts, is evidence against physicalist theories of consciousness and against other third-personal metaphysical pictures, including standard versions of dualism. List also argues that the vertiginous question implies a "quadrilemma" for theories of consciousness, where no theory of consciousness can simultaneously respect four initially plausible metaphysical claims – namely, "first-person realism", "non-solipsism", "non-fragmentation", and "one world" – but that any three of the four claims are mutually consistent.

See also

• Metaphysical naturalism
• Empiricism

• Metaphysical naturalism
• Cognitive science
• Consciousness
• Epiphenomenalism
• Hempel's Dilemma
• Monism
• Ontological pluralism
• Mary's Room
• Philosophy of mind
• Presentism
• Reductionism
• Supervenience
• Multiple realizability

References

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External links

• "Physicalism" entry by Daniel Stoljar in the Stanford Encyclopedia of Philosophy