I consider myself a (metaphysical) materialist or, to use the synonymous term that is more fashionable nowadays, physicalist, and I'm familiar with the academic literature on contemporary materialism/physicalism. But in no paper or book did I find really satisfying, fully adequate definitions of the central concepts of a material/physical object and of a material/physical property. (A material/physical property certainly isn't material/physical in the same sense as a material/physical object.) Does this mean that there actually aren't any such definitions, and that materialism/physicalism is therefore a virtually vacuous doctrine? Material/physical objects (substances) could be defined in terms of material/physical properties: x is a material/physical object =def x has some (intrinsic) material/physical properties. But then the big problem is how to properly define the concept of a material/physical property. I've been trying to devise and formulate a fully adequate definition of it for several years—but I always failed. Such a definition is particularly hard to come by because it mustn't render property dualism false by definition and physicalist property monism true by definition. It also mustn't rule out the possibility of panpsychism. So my question to you is: Is there any fully adequate definition of the concept of a material/physical property available, or is the intellectual search for it hopeless?

This is indeed a difficult question. If we say that a physical object is an object with intrinsic physical properties, then you are right: we have left ourselves with the question of what a physical property is. If we say that a physical object is an object with spatiotemporal properties (such as position and velocity), then someone who believed in irreducible minds or souls that have spatial locations could presumably still count as a physicalist, which seems inappropriate. If we say that a material object is an object that is made of matter, then we need an account of what matter is. Are electric fields made of matter? They have mass, after all. Would Newtonian space be made of matter? It doesn't seem like it would be ... but its existence does not compromise materialism, does it?

More generally, materialism and physicalism seem to be motivated by the idea that the entities described by physics are all of the entities that there are -- or, more precisely, are all of the fundamental entities there are. Another way to put this idea (that avoids the presupposition that there are fundamental entities) is that physicalism is the idea that all of the facts (or, at least, all of the contingent facts) are determined by the physical facts. Now, of course, the question is: what is a physical fact? Any specification of the particular kinds of properties that can figure in a physical fact would seem to be hostage to the fortunes of a future physics. To avoid any commitment to the kinds of facts that might appear in a final physics, we could say that physicalism is the idea that all of the (contingent) facts are determined by the facts that would appear in the final, complete physics. However, that way of putting the point presupposes that we understand what counts as "physics." This seems to raise exactly the questions that we were trying to get around.

One place where these matters are discussed is early in Bas Van Fraassen's book "The empirical stance." Van Fraassen argues that materialism (physicalism, naturalism...) are stances rather than views that could be true or false.

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