The following was written in partial fulfillment of the requirements of Dr. Greg Welty's Philosophy: Science and Religion class at Southeastern Baptist Theological Seminary.
The following was prepared as a one-page, single-spaced short response to a question from the readings for this class.
Scientific naturalism, as a worldview (not an instrumental technique applied in certain circumstances) is certainly question-begging. First, the claim that “the physical world is the only thing which exists” is fundamentally a philosophical and not a scientific claim. That is, if science is a broadly experimental approach to discovering truth about the physical world, it is incapable of determining whether a non-physical world exists, and it is not even asking—still less answering!—metaphysical questions about the nature of reality. The basic issues of epistemology, ontology, and ethics are themselves not subject to empirical analysis. Evidence from the natural world may certainly be useful and even helpful in considering these domains, but by definition cannot be finally determinative. For example: if the physical world is not the only thing which exists, what sort of purely physical test could demonstrate that? Likewise, if humans have cognitive access to spiritual realities, because they are dualist and not purely physical beings, they might have genuine non-physical experiential knowledge. No ontological, epistemological, or teleological claim is finally resolvable through merely physical testing; claims in such areas are finally philosophical and theological.
Second, the efficacy of science in the domain of explaining the physical world is in no sense evidence that it is a particularly effective way of describing all things. This is akin to suggesting that because musical notation is particularly effective for representing notes to be played, it is the only form of notation required; all written words should immediately be discarded, as should all computer programs. That is, the utility of one form of description or program of study for a given domain does not make it immediately applicable to or indeed at all relevant for other domains. Even with the context of scientific efforts, this is obvious: different techniques are used in observational astronomy than in ecological analysis, and different methods of analysis in assessing the claims of theoretical physics than in analyzing data from a given paleontological dig.
Third, and perhaps most importantly for current debates, the efficacy of science in describing the physical world provides no evidence whatsoever that the physical world is the only thing which exists. To suggest otherwise is simply to commit a basic logical fallacy. This is obvious if the premises and conclusion are laid out explicitly: The argument might be laid out so: “(P1) Science describes the physical world effectively. (P2) Science does not and cannot describe the non-physical world. (C) Therefore, the physical world is the only thing which exists.” But the conclusion clearly does not follow from the premises, even inductively. The argument might be modified into an inductive form: “(P1) Science describes the physical world effectively. (P2) Science has provided increased effectiveness in describing an ever-wider variety of phenomena over time. (P3) In so doing, science has found physical explanations of phenomena which at one time seemed intractable to such explanations. (C1) Therefore, science will at some point in the future find physical explanations for all phenomena. (C2) Therefore, there are no non-physical phenomena.” Even so strengthened, there are two major problems with the argument. First, C1 is an incredibly strong claim, and the purported evidence toward it in this form’s P3 is itself disputed. Moreover, even if C1 were granted, it would offer some evidence for C2 but would not prove it. There still might be reason to think that physical phenomena and their corresponding explanations were expressions of the will of a wise divine being, for example. Moreover, while claims for non-physical purposes for or fundamental explanations of physical mechanisms might then be on shakier ground in virtue of being apparently less simple, the physicalist would need to make a (philosophical) argument for the apparent scientific virtue of simplicity! There is no escape from claims which are themselves not even capable of being tested empirically.