Defining “Natural”: A Philosophical Problem for Discussion

This is something on which I could use some help.

Preface:

“Entities” is to be understood in the broadest possible way. Entities may be existent or non-existent, simple or complex, irreducible or reducible, emergent or fundamental,[1] mental or non-mental, material or immaterial, etc. (Can you think of any significant bases I haven’t covered here?)

Let’s use “naturalism” to refer to the ontological claim that no entities exist that are non-natural.

Something is “non-natural” iff it is not identical to, reducible to, or wholly composed of natural entities.

Aim:

For present purposes, what we want is a definition of “natural” that allows naturalism to be an internally coherent thesis that someone can legitimately defend as a defeasible, a posteriori hypothesis. Naturalists claim that naturalism is a contingent truth.

Preferably, our definition of “natural” will leave room for the class of natural entities to contain more than the class of physical entities. Naturalism should not automatically entail physicalism.

Method:

I take it that in order for naturalism to be a posteriori and a contingent truth, it must be possible to present an argument for naturalism that is not circular or question-begging. (Perhaps the argument will finally be judged unsound; what matters right now is not the truth value of naturalism but its alleged contingency.)

I take it that the best argument available for naturalism is an argument from the empirical, meta-scientific observation of explanatory completeness[2] something like what follows (this a specifically physicalist version of the argument; I want to explore ways to modify the argument to make it apply to more inclusive forms of naturalism):

Scientific research of the last hundred years or so has had great success in finding physical (hence, natural) explanations for observed phenomena. There is no longer any reason (so the argument goes) to postulate the existence of any special, non-physical entities in order to account for observable, physical effects. Hence, the thesis of

“the ‘causal closure’ or the ‘causal completeness’ of the physical realm,
according to which all physical effects can be accounted for by basic physical
causes (where ‘physical’ can be understood as referring to some list of
fundamental forces)”[3]

has been well-confirmed. The methodological consideration of simplicity thus justifies the ontological hypothesis that the only fundamental entities that exist are those entities which make up the subject matter of physics.

First Try:

The history of science may be taken to confirm physicalism [see above] or else the thesis that there are no unexplainable phenomena. (Note: by definition, “phenomena” is restricted to the realm accessible to our observation). So naturalism could be the claim that we don’t need to posit any queer, non-scientific, supersensible entities in order to give (efficient) causal explanations of any observable phenomena. (We may consequently be justified to infer that there are no such entitites.) Everything we can observe can in principle be explained by other things that we observe, without recourse to the unobservable.

If we said that to be “natural” is to be observable (“non-natural” = “unobservable”), could we call the claim that nothing non-natural is a necessary component of an (efficient) causal explanation a scientific discovery, a posteriori, or a contingent truth?

No. Because something is observable by definition insofar as it causally generates observable effects; and if this is right, then it is an analytic truth, known a priori, “discovered” on reflection rather than observation, that all necessary posits of scientific explanations are observable, or “natural” on the above definition. (If I’m wrong and something can be non-observable but generate observable effects–subatomic particles, for example–then we have to reject our definition of “natural” because we want subatomic particles to count as “natural”, since the physical is supposed to be the paradigm case of the natural.)

Conclusion: This try hasn’t worked because the key claim turns out not to be a confirmable, defeasible, scientific hypothesis but rather a conceptual truth.

Help Desired!!

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[1] By “fundamental” I intend “non-emergent”…can you please confirm or correct my terminology here?

[2] See David Papineau, “Naturalism”, §1.2-1.3, The Stanford Encyclopedia of Philosophy, http://plato.stanford.edu/. I call this observation “meta-scientific” because it is a general observation about the fruits of recent scientific inquiry, rather than a particular observation that occurs within a particular scientific research program.

[3] Papineau, “Naturalism”, §1.2.
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