Physicalism, Reductive and Nonreductive

Physicalism is a doctrine that asserts that ultimately only physical particulars exist. While physicalism and materialism are sometimes considered equivalent, the former is more ontologically open, for while materialism claims that everything is composed of matter, physicalism holds that everything is comprised ultimately of those entities assumed in the basic statements of fundamental physical theory (fields, particles, strings, or whatever). The thesis that only these physical entities exist is often termed ontological physicalism.

While ontological physicalism is often presupposed in the philosophical discussion, controversy arises about the properties possessed by these physical particulars. For example, what is the ontological status of putative mental properties? Are they reducible to underlying physical properties, or do they have a kind of being of their own? The reductive physicalist affirms, while the nonreductive physicalist denies, that mental properties are "nothing but" the physical. Broadly conceived, reductive physicalism asserts that all nonphysical properties are coextensive with particular physical properties. Nonreductive physicalism, on the other hand, conjoins the irreducibility of nonphysical properties (property dualism) to ontological physicalism.

Since the 1960s considerable doubt has been cast on the reductive physicalist project. In Ernest Nagel's (1901–1985) classic account, physicalist reduction occurs when nonphysical predicates are biconditionally connected to particular physical predicates such that the nonphysical property is instantiated when and only when a particular physical property is instantiated, (e.g., the mental property of a particular headache pain is instantiated when and only when a particular neuro-property is). However, one can imagine a silicon-based Martian having the same headache pain as an earthling, but because of the Martian's different neurophysiology, different physical properties will be instantiated. Because the same mental state seems to be realizable in different physical systems, reductive physicalism is called into question. Consequently, nonreductive physicalism has generally replaced reductive physicalism in the philosophy of mind. Accordingly, while the instantiation of an upper-level mental property is not reducible to the instantiation of a lower-level one, it is nonetheless realized by some lower-level property. Thus, instead of a type identity between property kinds, (every time mental property m is instantiated, physical property p is instantiated), there is a token identity between an instantiation of m and the instantiation of some physical property or other.

Issues of reductive and nonreductive physicalism are important in the science/theology discussion. If, as the natural sciences methodologically assume, only physical entities have causal powers and hence ultimately exist, then what kind of sense can be made of religion and its talk of God? In responding to this problem, nonreductive physicalism seems initially promising, for it holds with the natural sciences that only physical entities exist, and yet agrees with religion in claiming that there are irreducible nonphysical properties. If it can be shown that our mental life is irreducible to neuroscience, then insofar as religion concerns our mental life, it too is irreducible to the physical.

But large questions loom. Can upper-level properties be something more than mere epiphenomena, if they are token identical to physical properties that do all the causal work? Alternately, if physical properties do not do all the causal work, can dualism be avoided? Finally, if the irreducible mental is nonetheless completely realized by the physical, then in charting this physical realization, is one not offering a reductive explanation of the mental, and its religious experience, after all?

See also Materialism; Mind-brain Interaction; Naturalism; Reductionism; Supervenience

Bibliography

beckermann, ansgar. "introduction—reduction and nonreductive physicalism." in emergence or reduction? essays on the prospects of nonreductive physicalism, eds. ansgar beckermann, hans flohr, and jaegwon kim. berlin and new york: walter de gruyter, 1992.

davidson, donald. "mental events." in essays on actions & events. oxford: clarendon press, 1980.

kim, jaegwon. mind in a physical world: an essay on the mind-body problem and mental causation. cambridge, mass.: mit press, 1999.

murphy, nancey. "physicalism without reduction: toward a scientifically, philosophically, and theologically sound portrait of human nature." zygon 34 (1999): 551-572.

nagel, ernest. the structure of science: problems in the logic of scientific explanation. new york: harcourt, brace, and world, 1961.

dennis bielfeldt