What is the difference between Naturalism and Physicalism?

Question

I am trying to figure the difference between Naturalism and Physicalism. As far as I could tell, they were the same thing, except that physicalism (physicalist vs dualist) was the term used when discussing philosophy of mind and naturalism was the term used when discussing philosophy of religion (natural vs super-natural).

I came across a previous question: What is the difference between naturalism and materialism?. In the accepted answer to that post, it is stated that:

The branch called Ontological Naturalism focuses on how science can explain the world fully with physical laws.

This is pretty much a text book definition of physicalism - other than the fact that it doesn't refer specifically to the mind-body problem, so it seems that my original thought was confirmed. But in a second answer which purports to complement the accepted one, it is stated that:

naturalism does not presuppose materialism (or physicalism,..)

And then, quoting David Chalmers,:

allowing that ultimately the universe comes down to a network of basic entities obeying simple laws, and allowing that there may ultimately be a theory of consciousness cast in terms of such laws. If the position is to have a name, a good choice might be naturalistic dualism.

• On one hand physicalism and naturalism are basically the same thing: What ever we can observe in Nature is all there is (a monistic ontology), and Nature follows a set of rules that we are able to gradual discover.

• On the other hand, physicalism is a monistic ontology, while naturalism eventually allows for a dualist ontology.

My questions:

• The two answers are contradictory: Are physicalism and naturalism the same? or are they different? Which one is it?
• Even allowing for David Chalmers's Naturalistic Dualism, there still seems to be an inconsistency? Why does the mental warrant it's own ontology, while everything else doesn't? Why can't we have a triaistic ontology (matter, energy, and mental)? Or pentic ontology (baryonic matter, Fermionic matter, energy, logical, ethical)? Or any arbitrary number of ontologies?
• Doesn't Chalmers definition become circular? Naturalism is the ontology of whatever exists? If tomorrow we discover that angels and demons are real, than we just bring them into the fold and call it naturalism as well?

Answer 1

Naturalism in the broad sense is a very loose attitude, far looser than even materialism, let alone physicalism, because the notion of "nature" is left open to interpretation. Defined negatively as "not supernatural" it leaves room say for pantheism a la Spinoza with nature=God="substance of infinite attributes" (Spinoza is even sometimes described as "Epicurean materialist"). In this loose meaning naturalism expresses more a disposition towards a certain approach to intellectual inquiry, philosophical, scientific or even aesthetic, than any particular ontological, epistemological or methodological position, hence the need for those additional epithets to make it more specific. Goethe called himself a naturalist, criticized reductivism about living creatures, and argued for holistic science as "phenomenology of nature". So Chalmers is not off base to claim the mantle of Spinoza and Goethe and call himself a naturalist.

In analytic philosophy naturalism without qualifications usually refers to epistemological naturalism, a.k.a. naturalized epistemology of Quine, which subsumes philosophy, or at least epistemology, under natural science. This variety is closer to historical empiricism (Hume, Kant, Mill) than to any flavor of materialism or physicalism. Even Quine declaring himself a realist is accompanied with a redefinition of "realism" that does Kant proud:" Viewed from within the phenomenalistic conceptual scheme, the ontologies of physical objects and mathematical objects are myths. The quality of myth, however, is relative; relative, in this case, to the epistemological point of view", "The scientific system, ontology and all, is a bridge of our own making... But I also expressed my unswerving belief in external things — people, nerve endings, sticks, stones. This I reaffirm. I believe also, if less firmly, in atoms and electrons and classes."

In other words, epistemological naturalism has an as-if view of material and ideal ontologies (in 1940s Quine was an outright nominalist, but later acknowledged natural numbers as scientifically "indispensable", see Does Quine's dissolution of the Analytic/Synthetic distinction challenge mathematical realism?). In practice, naturalist attitude often predisposes one to accepting materialist (less so physicalist) positions in ontology, but "explaining the world fully with physical laws" refers to the phenomenal world and implies no metaphysical commitment to said ontology.

Answer 2

Naturalism has a range of meanings, and the equivocation of these various meanings is the source of your apparent contradiction.

In its broadest meaning, naturalism is just a committment to the "explore, speculate, test, revise" methodologies that use empiricism and reasoning, and the premise that either none or only a little of our universe is immune to this methodology. This is methodological naturalism, and it is accompanied by a belief in a continuum approach to science and metaphysics, as metaphysics would be primarily or entirely "natural". The most noteworthy recent advocate of this approach is Karl Popper, and as a "naturalist", and our definer of science, he advocated for a triplest ontology (mind, and ideas are separate planes from matter) all subject to naturalist investigation.

However, many materialists, and many physicalists, assume that only matter is subject to this methodology, and describe themselves as naturalists. This includes an assumption that mind, soul, gods, math, logic or some subset of these are "supernatural", in that they are immune to investigation either empirically or logically.

It is not just materialists who hold this narrow view of naturalism. Stephen J Gould's Non Overlapping Magisteria concept has been adopted by many dualists, who hold that the spiritual realm exists, but is not subject to naturalist evaluation.

Metaphysical naturalism takes this narrow approach to the "natural" and asserts that only those things which fit this narrow "natural" actually exist. However, as I noted, even "naturalists" themselves disagree on how narrow naturalism is. Most physicalists agree that mind and logic exist, but are just causally dervative on matter, rather than the materialist declaration of their non-existence. So even among metaphysical naturalists the definition is variable.