Physicalism

The Nature of Physicalism

Earlier physicalists—such as Thomas Hobbes—provided a substantive characterization of the nature of the physical as, for example, occupying space and/or possessing mass. With the development of physics, the emphasis changed. The objects and properties characterized by modern physics seemed very different from our everyday understanding of physical objects, yet it seemed a mistake to take developments in modern physics to prove that physicalism was incorrect. Thus modern day physicalists, such as J. J. C. Smart, sought to define physicalism in terms of physics. They recognized that physics may conceivably develop in ways that would recognize nonphysical entities and that not everything physical is identified by physics. [Page 601]For example, the properties of being a mammal or of being a chair seem to be physical but aren't identified by physics. So they eventually came up with a characterization on the following lines: A property is a broadly physical property if and only if either it is identified by a physics that sufficiently resembles our own current physics (where by this they mean the postulates of that body of physical theory broadly accepted in the late 20th and early 21st century, including the special and general theory of relativity and quantum mechanics) or it supervenes on those properties identified by physics (supervenience will be described below). The basic idea is that a physics that postulated nonphysical entities would be a significant departure from, and hence not resemble, current physics as just understood. Physical objects and events are those that only have physical properties in the specified sense. Narrowly physical properties are just those identified by physics of the type indicated.

Great energy was then devoted to identifying what kind of supervenience was involved. Supervenience is a type of covariation between members of specified families of properties, for example, between properties of arrangements of bricks and properties of being brick constructions such as walls. Although identity between properties is a limiting case of supervenience, supervenience does not require identity between them; otherwise, it would be ill-suited to the task at hand since it would require that all properties are identified by physics. Nor can this kind of supervenience be simply a lawful relationship between properties. Those who deny that physicalism is true don't have to deny that there is such a relationship between physical and nonphysical properties. For example, suppose you believed in ghosts and that, in the presence of ghosts, there would be a drop in temperature. Then there would be a lawful relationship between ghostly properties and physical ones but this, alone, would not make ghosts physical. Thus, many philosophers appealed to a metaphysically necessary relationship, for example, the kind that holds between having angles adding up to 180° and being three sided. No matter how things might otherwise might be, the thought ran, if two universes were identical in their arrangement of the properties identified by physics (and no other properties were added), then the distribution of all other properties, including, specifically, mental properties, would be fixed.

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