Substance dualism is defined as being different from physicalism because it posits 2 different categories of substances in the world as opposed to one category.

But throughout the ages, all sorts of physicalist theories have made use of different categories of substance: Matter vs energy, protons/neutrons/electrons/, the dozens or more of fundamental particles (bosons, leptons, 12 types of quarks, etc...) used in particle physics, wave-particle duality, etc...

So what makes substance dualism metaphysically different from scientific theories which describe different categories of substances?


it is my understanding that physicalism denies the existence of the non-physical category of substance. the physicalist or materialist would disputet the dualist's belief that their consciousness is anything more than or other than a manifestation of physical processes (Dennett has said that we are automatons that "think" we have free will). they say that there is no substance to our consciousness other than the physical processes.

the dualist would say that there is something substantive about our consciousness that transcends the physical processes.

and i think that the physicalists would deny that there exists a different category of physical reality other than energy, subatomic particles, and the such. they would say all of these things simply exist in reality and that their interactions have a completely physical root. (no magic forces, invisible forces maybe, but not having a non-material source.)


It can be framed as a matter of semantics, but it tends to not be framed that way because the semantics in question are rather profound ones. Concepts such as determinism, freewill, God, and several other concepts are rolled up into the debate.

I find there are points of view which make this issue much less profound, reducing it more towards something which someone might call "a matter of semantics" without feeling like they are underestimating it. From some points of view, the mere idea that we could be products of a universe which is governed by unbreakable laws is an affront to freewill, even though they may admit that it would be impossible to tell the difference empirically. From other points of view, they're just different semantics for a word yielding the same result. It all depends on how essential the semantics of some concepts are to your beliefs.

For an example of how important such semantics can be, look at science's evolution argument. It is often stated that "evolution is true." Nearly everyone in the science community agrees that "there is a large body of evidence supporting the theory of evolution," but transitioning from that statement to "evolution is true" proves to be a very strong divisive argument. Some, like myself, will argue that such a claim strips the mathematically correct defenses for a scientific claim clear away, forcing one to rely on other sources of reason to defend the claim. Others will argue that the abductive step from one statement to the other is justified (implying they do not need to admit that anyone might think otherwise). Others will emphatically argue until they are blue in the face that there was no abductive step, and that "lots of evidence" is good enough to directly imply "true," and that anyone who tries to slide some Greek words between the two is just trying to play games. All parties will agree that there is no epistomological difference between the effects of the three positions, but there can be downright violent debates as to the semantic differences between the positions.

And compared to the question of physicalism vs dualism, the question of evolution is a small fry semantic debate.


Though I am uneasy about the term "substance" in this debate, it seems to me that Kant is perhaps the only truly consistent, plausible dualist.

He posits a unity of all things knowable, including the "physical" by any interpretation, and the existence of the noumenal,"unknowable" realms, which can never be reduced to the phenomenal. Though we may picture this as ghostly entities "outside" of conceptual grasp, it may be more feasible to think of it as a frequency or "scale" exceeding any possible measurement or a "speed" faster than light. Yet there are moral and other "reasons" within his system for positing such "unknowables." They can't just be Occamized.

In other respects, it is questionable whether even Descartes is a proper dualist, since he must posit some "pineal gland" or whatnot carrying out mind-matter conversions. (You are right, it appears to be largely a "semantic" problem, but I'm not sure that really says anything or washes out the complexity.) Since dualism suggests substances that can "never" interact "anywhere," we might suspect that "infinity" is involved, which cannot really sit within any physicalist system.

There are many candidates for things "outside" of any physical-causal sovereignty. Infinity, negentropy, possible worlds, utopia, god, entanglement. Noumena or Wittgenstein's "whereof we cannot speak." Somewhere over the rainbow. Are these irreducibly "dual" to the matter-energy continuum? Or are they unified in the consciousness that can conceive of them? If so, would that make schizophrenia the basic substance dualism?

Obviously no satisfactory "ontological proof" can apply to anything so construed. To me it remains, so far, a tangle. And Kant strikes me, for now, as the most coherent, workable expression of a fundamental dualism. So I cannot accept that it is "merely semantic." And anyone who could convincingly reduce such a swarm of problems to "semantics" would, I suppose, vault into philosophical prominence.


Aristotle was the first philosopher to describe the notion of ousia, that is substance; it is that which is self-subsistent and depends on nothing else - which is one reason why it's been imported into theology as a part of theorising on the nature of God; for example, Spinoza calls God the neccessary substance.

In Physics, though matter as a substance is a kind of analogue; but not quite - matter is not independent of energy, or momentum; or time and space; to correspond with the traditional idea one notion ought to be selected as foundational.

Spinoza, following Descarte chose the notion of extension - given that space, time, matter and motion have magnitude; but given his theology he represented as a mode of a substance, rather than as a substance per se.

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