In metaphysics, physicalism is the view that everything is physical, that there is nothing over and above the physical, and that everything supervenes on the physical. It stands in direct opposition to idealism, which asserts that reality arises from the mind. Physicalism is a form of ontological monism—a single-substance account of the nature of our universe's reality (physicalism is open to the possibility of different universes with different physics, and is open to the possibility of causal openness via a foundational logical mechanism or mechanisms), in contrast to "two-substance" (mind–body dualist) or "many-substance" (pluralist) views. Physicalism is closely related to naturalism, though important distinctions exist between them.
Physicalism is also 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, spacetime, exotic matter, structure, physical processes, information, state, and forces, among other things, as described by physics and other sciences.
According to the PhilPapers Survey 2020, physicalism is the majority view among philosophers, at 51.9%, but there is also significant opposition to it.
Outside of philosophy, physicalism can refer to the preference or viewpoint that physics is the best or 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.See Bennett and McLaughlin, 2011Davidson D., 1993, “Thinking Causes”, in Heil and Mele. 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.
Type physicalism
Type physicalism, also known as mind-body identity theory, holds that mental events can be grouped into types that correlate with types of physical events. For instance, one type of mental events, such as pain, correlates with a particular type of physical events, such as C-fiber firings. On this account, all instances of pain correspond to situations where C-fibers are firing. Type physicalism can be understood as the position that there is an identity between types: any mental type is identical with some physical type.
A common argument against type physicalism is the problem of multiple realizability. Multiple realizability posits that the same mental state can be realized by different physical states. Another way to put it is that there is a many-to-one mapping from physical states to mental states.
Token physicalism
Token physicalism is the proposition that every particular mental event is a particular physical event (token physical event) but that there is no type-to-type mapping between mental events and physical events. The most common example of token physicalism is Davidson's anomalous monism.Davidson, D. (1970) "Mental Events", in Actions and Events, Oxford: Clarendon Press, 1980. One of token physicalism's strengths is that it is compatible with multiple realizability. Mental states such as pain may be realized in any number of widely different physical events, without any type-like similarity between these physical events.
Reductive and non-reductive physicalism Reductionism
In the philosophy of mind, reductionism is commonly understood as the reduction of psychological phenomena to physics and chemistry. In a simplified form, reductionism implies that a system is nothing but the sum of its parts.Thomas Nagel (2012). Mind and Cosmos: Why the Materialist Neo-Darwinian Conception of Nature is Almost Certainly False. Oxford University Press. pp. 4–5. . There are both reductive and non-reductive versions of physicalism (reductive physicalism and non-reductive physicalism). Reductive physicalism is the view that mental states are nothing over and above physical states and are reducible to physical states.
Emergence
Emergentism is a theory that became popular in the early 20th century.Van Gulick, Robert. "Emergence". Internet Encyclopedia of Philosophy. University of Tennessee. Notions of strong emergence are commonly found in accounts of non-reductive physicalism. A property of a system is said to be emergent if it is a new outcome of some of the system's other properties and their interaction while it is itself different from them. Emergentism emphasizes that the whole is more than the sum of its parts.O'Connor, Timothy and Wong, Hong Yu (eds.), "Emergent Properties", The Stanford Encyclopedia of Philosophy (Summer 2015 Edition), Edward N. Zalta (ed.) In the context of the philosophy of mind, emergence is often thought to entail property dualism.Bratcher, Daniel (1999). "David Chalmers' Arguments for Property Dualism". Philosophy Today. 43 (3): 292–301. doi:10.5840/philtoday199943319
Arguments against physicalism Knowledge argument
Though there have been many objections to physicalism throughout its history, many of them are concerned 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 Cameron Jackson, titled "Mary's room".Jackson, Frank (1982). "Epiphenomenal Qualia". Philosophical Quarterly. 32 (127): 127–136. doi:10.2307/2960077. JSTOR 2960077.
The argument asks us to consider Mary, a girl who has been forced to discover the world from a black-and-white room via a black-and-white television monitor throughout her life. She has access to books containing all physical knowledge. During her time in the room, she learns all the physical facts about the world, including all the physical facts about color. To a physicalist, it would seem that this entails Mary knowing everything about the world. But once she is let out of the room and into the world, it becomes apparent that there were things Mary did not know about the world, such as the feeling (the qualitative 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 response, developed by Lawrence Nemerow and David Lewis, is known as the ability hypothesis. The ability hypothesis distinguishes 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", and says that all Mary gains from seeing the world in color is knowledge-how. According to this response, Mary does gain knowledge from her experience, but it is not the propositional knowledge required for the knowledge argument to be logically sound.
Argument from philosophical zombies One commonly issued challenge to a priori physicalism and physicalism in general is the "conceivability argument", or zombie argument.See Chalmers, 2009. The conceivability argument runs roughly as follows:
According to physicalism, everything in our world (including consciousness) is physical. Thus, if physicalism is true, a metaphysically possible world in which all physical facts are the same as in the actual world contains everything that exists in the actual world. In particular, conscious experience exists in such a world. We can conceive of a world physically indistinguishable from our world but in which there is no consciousness (a zombie world). From this it follows that such a world is metaphysically possible. Therefore, physicalism is false. (This follows from (2) and (3) by modus tollens.)See Chalmers, 2009
The possibility of philosophical zombies (p-zombies) entails that mental states do not supervene upon physical states, and thus that physicalism is false. Australian philosopher David Chalmers argues that the conceivability of a zombie entails a metaphysical possibility.
Physicalist response Galen Strawson argues that it is impossible to establish the conceivability of zombies, so the argument, lacking its first premise, fails.
Daniel Dennett 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". He coined the term "zimboes"—p-zombies that have second-order beliefs—in arguing that p-zombies are incoherent:Dennett 1995; 1999 "Zimboes thinkZ they are conscious, thinkZ they have qualia, thinkZ they suffer pains—they are just 'wrong' (according to this lamentable tradition), in ways that neither they nor we could ever discover!" In The Unimagined Preposterousness of Zombies (1995), Dennett compares consciousness to health.
Michael P. Lynch argues that the zombie conceivability argument forces us to either question whether we actually have consciousness or accept that zombies are impossible. If zombies falsely believe they are conscious, how can we be sure we are not zombies? We may believe we have conscious mental states when in fact we merely hold a false belief. Lynch thinks denying the possibility of zombies is more reasonable than questioning our own consciousness.Lynch, Michael P. (2006). Zombies and the case of the phenomenal pickpocket. Synthese 149 (1):37-58.
Daniel Stoljar has proposed what he calls "the phenomenal concept strategy".See Stoljar, 2005 Roughly, this strategy attempts to show that only the concept of consciousness—not the property—is in some way "special" or sui generis. Essentially, he believes we are less likely to question physicalism if we can figure out why we think there is a difference between consciousness and physical processes.cf. Stoljar, 2005
Hempel's Dilemma
Physicalists have traditionally opted for a "theory-based" characterization of the physical in terms of either current physicsSee e.g., Smart, 1978; Lewis, 1994. or a future (ideal) physics.See e.g., Poland, 1994; Chalmers, 1996; Wilson, 2006. Hempel's Dilemma (named after the philosopher of science Carl Gustav Hempel) attacks physicalism by arguing that both of these approaches are problematic. If, on the one hand, we define the physical by reference to current physics, then physicalism is very likely to be false because it is very likely (by pessimistic meta-inductionsee Vincente, 2011) that much of current physics is false. If, on the other hand, we define the physical in terms of a future (ideal) or completed physics, then physicalism is hopelessly vague or indeterminate.See Hempel, 1969, pp.180-183; Hempel, 1980, pp.194-195.
Physicalist response