Methodological Naturalism and Philosophical Naturalism: Clarifying the Connection

Barbara Forrest

During the past two decades, an attack has been waged in the United States against both methodological naturalism and philosophical naturalism. The charge is that methodological naturalism, by excluding a priori the use of supernatural agency as an explanatory principle in science, therefore requires the a priori adoption of a naturalistic metaphysics. The disquiet over naturalism is rooted most immediately in the implications of Darwin’s theory of evolution; hence, the specific focus of the attack against naturalism is evolutionary biology.1 The aim of this article is to examine whether methodological naturalism entails philosophical naturalism.2 This is a fundamentally important question; depending on the answer, religion in the traditional sense—as belief in a supernatural entity and/or a transcendent dimension of reality—becomes either epistemologically justifiable or unjustifiable. My conclusion is that the relationship between methodological naturalism and philosophical naturalism is not such that philosophical naturalism is a mere logical possibility, whereas, given the proven reliability of methodological naturalism in yielding knowledge of the natural world and the unavailability of any method at all for knowing the supernatural, supernaturalism is little more than a logical possibility. Philosophical naturalism is emphatically not an arbitrary philosophical preference but rather the only reasonable metaphysical conclusion—if by “reasonable” one means both empirically grounded and logically coherent.

Definition of Naturalism

I am addressing the subject of naturalism in contrast to traditional supernaturalism, which means belief in a transcendent, nonnatural dimension of reality inhabited by a transcendent, nonnatural deity.

I shall use “methodological naturalism” and “philosophical naturalism” to mean what Paul Kurtz defined them to mean in the first and second senses, respectively:

First, naturalism is committed to a methodological principle within the context of scientific inquiry; i.e., all hypotheses and events are to be explained and tested by reference to natural causes and events. To introduce a supernatural or transcendental cause within science is to depart from naturalistic explanations. On this ground, to invoke an intelligent designer or creator is inadmissible….

There is a second meaning of naturalism, which is as a generalized description of the universe. According to the naturalists, nature is best accounted for by reference to material principles, i.e., by mass and energy and physical-chemical properties as encountered in diverse contexts of inquiry. This is a non-reductive naturalism, for although nature is physical-chemical at root, we need to deal with natural processes on various levels of observation and complexity: electrons and molecules, cells and organisms, flowers and trees, psychological cognition and perception, social institutions, and culture.3

Methodological naturalism and philosophical naturalism are distinguished by the fact that methodological naturalism is an epistemology as well as a procedural protocol, while philosophical naturalism is a metaphysical position. Although there is variation in the views of modern naturalists, Kurtz’s definition captures these two most important aspects of modern naturalism: (1) the reliance on scientific method, grounded in empiricism as the only reliable method of acquiring knowledge about the natural world, and (2) the inadmissibility of the supernatural or transcendent into its metaphysical scheme. Kurtz’s definition is consistent with Sidney Hook’s earlier one:

[T]here is only one reliable method of reaching the truth about the nature of things…. [T]his reliable method comes to full fruition in the methods of science … and a man’s normal behavior in adapting means to ends belies his words whenever he denies it. Naturalism as a philosophy not only accepts this method but also the broad generalizations which are established by the use of it; viz, that the occurrence of all qualities or events depends upon the organization of a material system in space-time, and that their emergence, development and disappearance are determined by changes in such organization.

. . . [N]aturalism as a philosophy takes [the word material] to refer to the subject matter of the physical sciences. Neither the one [philosophical naturalism] nor the other [science] asserts that only what can be observed exists, for many things may be legitimately inferred to exist (electrons, the expanding universe, the past, the other side of the moon) from what is observed; but both hold that there is no evidence for the assertion of anything which does not rest upon some observed effects.4

Scientific Views of Naturalism

Since methodological and philosophical naturalism are founded upon the methods and findings, respectively, of modern science, philosophical naturalism is bound to take into account the views of scientists. As Hilary Kornblith asserts, “Philosophers must be … modest … and attempt to construct philosophical theories which are scientifically well informed.”5

The methodology of science is the only viable method of acquiring reliable knowledge about the cosmos. Given this fact, if there is no workable method for acquiring knowledge of the supernatural, then it is procedurally impossible to have knowledge of either a supernatural dimension or entity. In the absence of any alternative methodology, the metaphysical claims one is entitled to make are very strictly limited. Moreover, the philosophical naturalist, without making any metaphysical claims over and above those warranted by science, can demand from supernaturalists the method that legitimizes their metaphysical claims. In the absence of such a method, philosophical naturalists cannot only justifiably refuse assent to such claims but can deny—tentatively, not categorically—the existence of the supernatural, and for the same reason they deny the existence of less-exalted supernatural entities such as fairies and ghosts: the absence of evidence.

The metaphysical adequacy of supernaturalism is inversely proportionate to the explanatory power of science. The more science successfully explains, the less need or justification there is for the supernatural as an explanatory principle. E.O. Wilson asserts that the explanatory power of science diminishes the metaphysical adequacy of supernaturalism by explaining even religion:

Most importantly, we have come to the crucial stage in the history of biology when religion itself is subject to the explanations of the natural sciences. . . . Sociobiology can account for the very origin of mythology by the principle of natural selection acting on the genetically evolving material structure of the human brain.

If this interpretation is correct, the final, decisive edge enjoyed by scientific naturalism will come from its capacity to explain traditional religion, its chief competitor, as a wholly material phenomenon.6

However, many people reject the application of scientific method to the phenomenon of religion and, though they adopt the methodology of naturalism to inquire about a natural entity or object or to solve a practical problem, they simultaneously assent to existential claims about the supernatural. One must recognize that invoking supernatural explanations is illegitimate because of the procedural impossibility of ascertaining the facticity of the supernatural cause itself, not to mention its intervention in the chain of natural causes. This points to the metaphysical implications of methodological naturalism: if supernatural causal factors are methodologically permissible, the cosmos one is trying to explain is a nonnatural cosmos. Conversely, if only natural causal factors are methodologically and epistemologically legitimate as explanations, then only a naturalist metaphysics is philosophically justifiable. Comprehending the universe in a scientific manner is the goal of philosophical naturalism.

Given the procedurally necessary exclusivity of methodological naturalism in science and the unavailability of any other workable method for grounding any claims with existential import, any metaphysical view of the cosmos other than the naturalistic one is epistemologically unjustifiable.

The point is that, from both an epistemological and a methodological standpoint, supernaturalism has not proved its mettle, whereas methodological naturalism has done so consistently and convincingly. Supernaturalism has provided neither the epistemology nor the methodology needed to support its metaphysics, whereas naturalism has, although the invitation to supernaturalism to do likewise is a standing one, as Steven Schafersman indicates: “Except for humans, philosophical naturalists understand nature to be fundamentally mindless and purposeless. . . . Of course, this doesn’t eliminate the possibility of supernatural mind and purpose in nature; the only requirement would be the demonstration of its existence and mechanism, which is up to the supernaturalist to provide. We are still waiting.”6

Methodological Naturalism in Philosophy

Naturalist philosophers ground their philosophical naturalism in both the failure of the supernaturalist to meet Schafersman’s challenge and in the success of methodological naturalism in science. This is because the reliability of knowledge depends on the method by which it is obtained, and as Schafersman says, “Science, solely because of its method, is the most successful human endeavor in history. The others don’t even come close.”8

The upshot is that methodological naturalism—the exclusive reliance upon scientific method for a cumulative explanation of the natural world—does provide an epistemologically stable foundation for a metaphysics. Methodological naturalism enables us to accumulate substantive knowledge about the cosmos from which ontological categories may be constructed.9

Methodological naturalism does exclude the supernatural as an explanatory principle because it is unknowable by means of scientific inquiry, whereas philosophical naturalism, both by definition and because of the methodological and epistemological inaccessibility of the supernatural, excludes the latter from its ontological scheme. Even though there are some variations among naturalists, the following statements by Sidney Hook are not likely to be contested: “Scientific method is the refinement of the canons of rationality and intelligibility exhibited by the techniques of behavior and habits of inference involved in the arts and crafts of men…. The systematization of what is involved in the scientific method of inquiry is what we mean by [methodological] naturalism, and the characteristic doctrines of [philosophical] naturalism like the denial of disembodied spirits generalize the cumulative evidence won by the use of this method.”10

These may well sound like fighting words to the supernaturalist, and since those who wish to allow the supernatural as an explanation cannot produce conclusive evidence that it exists, their insistence upon appealing to it sometimes amounts to a challenge to the naturalist to produce evidence that it does not exist or that it is not a causal factor in natural phenomena. However, the challenge is empty—first, because both the methodological and the ontological burdens of proof fall upon the supernaturalist, and, second, because proving the nonexistence of the supernatural is, by the nature of the task, impossible. Not only is it not the aim of methodological naturalism to prove the nonexistence of the supernatural, but the attempt to prove a negative existential claim in any event makes no sense: nothing can count as positive evidence of nonexistence. Hook cites the challenge and responds to it:

Let the naturalist prove [says the challenger] . . . that there can be no other kind of knowledge, that there can be none but empirical fact! And unless he can prove it, he is a question-begging a priorist. . . .

But here, too, the naturalist need undertake to do no such thing. Is there a different kind of knowledge that makes … [the supernatural] an accessible object of knowledge in a manner inaccessible by the only reliable method we have so far successfully employed to establish truths about other facts? Are there other than empirical facts, say spiritual or transcendent facts? Show them to us. . . .

Is there a method discontinuous with that of rational empirical method which will give us conclusions about what exists on earth or heaven, if there be such a place, concerning which all qualified inquirers agree? Tell us about it.11

Hook asserts that “the crucial point … is that we are not dealing with a question of pure logic but of existential probability…. There is a reasonable habit of inference with respect to belief or disbelief about natural fact which we follow with respect to supernatural fact. And it is still a reasonable habit of belief despite the claim that the supernatural fact is of a different order. For however unique it is, . . . it is reasonable to extend the logic and ethics of discourse to it.”12 He further emphasizes “a weighty point” by saying that “whoever says that … [the supernatural] exists must give reasons and evidence. The burden of proof rests on him in the same way that it rests on those who assert the existence of anything natural or supernatural…. It rests with the supernaturalist to present the evidence that there is more in the world than is disclosed by our common empirical experience.”13

Methodological naturalism does not disallow the logical possibility that the supernatural exists. To assert categorically that there is no dimension that transcends the natural order is to assert that human cognitive capabilities are sufficient to survey the whole of what there is; such a claim would amount to epistemological arrogance. But neither does methodological naturalism allow that mere logical possibility is sufficient warrant for the attribution of existence. At least the naturalist position is well established with respect to the kind of cognitive capabilities we do have. The supernaturalist, on the other hand, makes an assertion for which there is no epistemological justification when claiming that humans can know in any sense other than the natural one.

Therefore, the belief of the supernaturalist is on neither a logical nor an evidential par with the disbelief of the naturalist. What Hook says about the existence of God can just as well be used here with reference to any supernatural belief:

The admission that the existence of God cannot be demonstrated is often coupled with the retort that neither can his non-existence be demonstrated—as if this puts belief and disbelief on an equally reasonable footing, as if no distinction could be made between the credibility of purely logical possibilities, i.e., of all notions that are not self-contradictory. It is a commonplace that only in logic and mathematics can the non-existence of anything be “demonstrated.” If we are unjustified in disbelieving an assertion save only when its contradictory is demonstrated to be [
logically] impossible, we should have to believe that the universe is populated with the wildest fancies. Many things may exist for which we can give no adequate evidence, but the burden of proof always rests upon the individual who asserts their existence.14

Supernatural claims are existential claims, which is to say that they have existential import and so are subject to the same evidentiary requirements as claims about the natural order.15 Yet despite this, even though no method that does not depend upon empirical verification has ever been demonstrated for ascertaining conclusively the truth of existential claims, supernatural claims are beyond the reach of these requirements. Paradoxically, supernatural claims are the kind of propositions for which empirical evidence is required but impossible to obtain. The cognitive apparatus has not been identified through which one can know the supernatural.

Existential possibility is easy to specify with respect to empirically verifiable propositions. For example, in order for a winged horse to be existentially possible, the concept of a winged horse must be logically consistent—that is, thinkable without contradiction, which it is, and the gene necessary for wings must be present in the equine genome, which it is not. Therefore, a winged horse is existentially impossible, although not logically so. The ontological conditions are physical, but they do not in fact obtain. On the other hand, a chicken with teeth is a genuine existential possibility since the concept is logically consistent and chickens do in fact have a gene for teeth that merely remains unexpressed.

What analogous conditions may be specified for the existential possibility of supernatural entities? Again, there must be no logical contradictions in the concept of a supernatural entity. So, for example, the concept of a being that can exist without physical substance of some kind must be thinkable. Yet even the concept is not clearly possible in this first respect. If one is thinking of something with no measurable physical dimensions or detectable physical presence, one can plausibly argue that one is thinking about nothing. Even if the stipulation is made that a nonphysical, supernatural entity is detectable only by its physical effects, one is still faced not only with the traditional, irresolvable dualism but with the problem that one can, even in principle, detect only the phenomena that are being question-beggingly designated as “effects” and not the supernatural phenomenon that is posited as the cause. Therefore, not only are the questions of both existence and causal efficacy begged, but one is still essentially thinking about something that can simultaneously be conceived as both “something” and “nothing,” a logical impossibility.

The logical difficulties aside, what ontological conditions can be specified for the existential possibility of a supernatural entity? In order for a nonphysical, supernatural entity to exist, what must obtain? Such describable, specifiable, and necessary conditions do not seem to be available. The mind draws a blank.

If one is concerned with the justification of belief in terms of truth and falsity, such commitment must be accompanied by some positive evidence that points to the truth of supernatural belief. There must be empirical evidence for any claim with existential import, and any area of human thought, including religion, in which existential claims are made is subject to the criteria by which existential claims are tested.

Clearly, the problem of whether the supernatural is an existential possibility is not merely a methodological problem but also the epistemological one of how the truth of supernatural propositions is to be ascertained. Sidney Hook asks, “Are the laws of logic and the canons of evidence and relevance any different in philosophy from what they are in science and common sense?”16 His answer is that the rules of logical reasoning and evidence do not change simply because that which is subject to scrutiny is asserted to be beyond their reach. The minute an adherent of such a claim asserts its truth, the same rules apply. Every area of human inquiry is subject to the same logical and evidential analyses, and the person who maintains that the supernatural is not subject to the traditional rules of logic and evidence bears the burden of producing those that are relevant. Methodological naturalism, on the other hand, asserts the continuity of analysis, meaning that, in turn, philosophical naturalism asserts ontological continuity—a cosmos without the ontological bifurcations of supernaturalism. This position carries no burden of proof of any kind with respect to the supernatural, for it makes no existential claims over and above what can be empirically established by universally applicable methods.

These difficulties suffice to explain why supernaturalism cannot be appealed to in explanation of natural phenomena, whereas the demonstrated success of methodological naturalism suffices to show why it is the only justifiable explanatory principle. According to Hook, “This sounds very dogmatic, but is really an expression of intellectual humility that seeks to avoid unlimited credulity. It does not doubt that we possess scientific knowledge but leaves open the question of what we can have knowledge about…. Such humility does not assert that the experience of knowledge exhausts all modes of experience or that scientific knowledge is all-knowing.”17

The methodological naturalist is concerned with what is to count as unambiguous confirmation for an existential claim. Methodological naturalism does not provide an exhaustive inventory of what exists and what does not. Rather, its specific aim is to discern and specify any aspects of reality for which there is sufficient warrant. It permits the cumulative gathering and grounding of information about the bounded field we call the “natural world,” the epistemological boundary of which is constituted by its empirical accessibility. So in adopting the methodology of science, we are able to make defensible pronouncements about what exists in the natural order but about nothing that may transcend it. For the latter type of claim, we would need another method.

Philosophical Naturalism

Understanding methodological naturalism as the adoption of a skeptical temperament that emphasizes the scientific analysis of all areas of human inquiry, we now may examine the precise nature of the connection between methodological naturalism and philosophical naturalism.

For the philosophical naturalist, method is everything, so philosophical naturalism stands or falls with its reliance on methodological naturalism. Kornblith acknowledges philosophical naturalism’s reliance upon scientific method: “In metaphysics . . . we should take our cue from the best available scientific theories…. Current scientific theories are rich in their metaphysical implications. The task of the naturalistic metaphysician . . . is simply to draw out the metaphysical implications of contemporary science. A metaphysics which goes beyond the commitments of science is simply unsupported by the best available evidence…. For the naturalist, there simply is no extrascientific route to metaphysical understanding.”18

Adopted in the sciences because of its explanatory and predictive success, methodological naturalism is the intellectual parent of modern philosophical naturalism as it now exists, meaning that philosophical naturalism as a worldview is a generalization of the cumulative results of scientific inquiry. With its roots in late nineteenth-century science in the aftermath of Darwin’s On the Origin of Species, it is neither the a priori premise nor the logically necessary conclusion of methodological naturalism but the well-grounded a posteriori result. Yet because the philosophical naturalist begins with method, not metaphysics, methodological naturalism does impose constraints on what can be included in philosophical naturalism’s metaphysical scheme, constraints necessitated by its empiricist epistemology. Methodological naturalism need not (and does not) assume a priori that empiricism is the only conceivable avenue of truth or that intuition and revelation are nonexistent and, therefore, nonfunctional as forms of cognition. It functions in the absence of convincing evidence that intuitive or revelatory claims are genuinely cognitive and in the absence of any clear epistemological or metaphysical progress made on the basis of such claims. Likewise, it functions not only in the absence of any clear consensus regarding the ontological status of the supernatural or supernatural entities but in the unlikelihood that there is any way to reach a consensus. The only way to make any existential claims beyond those warranted by methodological naturalism is to produce the methodology by which these claims can be legitimately credited with belief. If that method cannot be produced, then any claims that cannot be justified by means of methodological naturalism cannot be warranted at all.

So then, how does naturalism move from method to metaphysics? Exclusive methodological naturalism does have metaphysical implications, and the metaphysical implications of the exclusive use of scientific method are the same, that is, philosophical naturalism, whether the latter is presupposed in an a priori fashion or whether it is a generalization founded on the result of the method’s consistent application. Insofar as methodological naturalism can accept as evidence for belief only what scientific method judges reliable, it does define what is an acceptable worldview by limiting what one can justifiably assert.

Although philosophical naturalism is not logically entailed by methodological naturalism, there are a number of other possible relationships between methodological naturalism and philosophical naturalism. The first possibility is that methodological naturalism merely permits, or is logically consistent with, philosophical naturalism. Though true, this claim is completely trivial and, as such, provides no substantive reason to link the two at all.

The second but very far-fetched possibility is that methodological naturalism logically precludes philosophical naturalism because, as previously noted, a claim of entailment would require omniscience. This possibility is untenable since philosophical naturalism makes no claim of omniscience. It rests on methodological naturalism as the necessary condition of reliable knowledge of the natural world but not as exhaustive of what can be known.

The third possibility is that methodological naturalism is not connected in any essential way either to philosophical naturalism or any other metaphysical view but that it is compatible with all and prescriptive of none. Certainly, it is possible to compartmentalize one’s thinking, acknowledging methodological naturalism as the only viable methodology with respect to the natural world, while simultaneously believing in, for example, the existence of a supernatural world. But this alternative presupposes the simultaneous possibility of a unitary, empirical methodology and a dualistic metaphysics consisting of a natural world within the framework of or ontologically contiguous with the supernatural. Either it requires the denial of the need for another methodology and epistemology or it implies that there is an additional methodology and a different epistemology for the supernatural. Moreover, the two methodologies and epistemologies must be procedurally and logically compatible.

Since the claim that methodological naturalism is compatible with anything other than philosophical naturalism requires the so-far indefensible claim that there are an additional but logically compatible methodology and epistemology, the fourth possibility constitutes the only viable relationship between methodological naturalism and philosophical naturalism, which is this: taken together, the (1) proven success of methodological naturalism combined with (2) the massive body of knowledge gained by it, (3) the lack of a comparable method or epistemology for knowing the supernatural, and (4) the subsequent lack of any conclusive evidence for the existence of the supernatural yield philosophical naturalism as the most methodologically and epistemologically defensible worldview.

This is where philosophical naturalism wins—it is a substantive worldview built on the cumulative results of methodological naturalism, and there is nothing comparable to the latter in terms of providing epistemic support for a worldview. If knowledge is only as good as the method by which it is obtained, and a worldview is only as good as its epistemological underpinning, then from both a methodological and an epistemological standpoint, philosophical naturalism is more justifiable than any other worldview that one might conjoin with methodological naturalism.

Philosophical Naturalism’s Ontological Categories

In the face of what I consider a compelling case for philosophical naturalism, I must also point out that philosophical naturalism is not an epistemologically airtight metaphysics for two reasons: (1) since it tracks the developments of science and depends upon its methodology, it is marked by not only the groundedness but also the tentativity of scientific understanding, and (2) neither can it be a guaranteed certainty until the nonexistence of the supernatural can be conclusively established. But this lack of epistemological certainty is emphatically not a weakness but rather the strength of philosophical naturalism. One never has “proof” of a comprehensive worldview if proof is defined strictly as logical demonstration, and exactly the same is true of any comprehensive metaphysical view, meaning that none enjoys the security of absolute certainty.

The problem with the demand that a worldview be privileged with a priori certainty is that if one starts with nonempirical basic beliefs—assumptions gleaned from introspection, conceptual analysis, or deduction—there is no guarantee that any basic belief, any of the contents of introspective reflection, any of the concepts analyzed, or any of the premises from which deductions are derived will be at all consistent with human experience or with science. What is needed is a metaphysics in which, very simply (1) there are no logical contradictions and (2) there is the greatest evidential justification—in short, one that places the least strain on rational credibility. Absolute certainty is not required, nor is it even possible given naturalism’s reliance upon science for its ontological categories. Moreover, given that philosophical naturalism, a generalization of the results of scientific method, consequently shares the advantage of the self-correction of science, a priori certainty is not even desirable.

Philosophical naturalism, rather than constructing a world-view from a priori ontological categories, constructs a worldview ordered by categories constructed from the ground up, so to speak, on the basis of empirically ascertained knowledge of nature; its categories are just as stable, or just as fluid, as scientific explanations themselves. Actually, except for its one most stable category, “nature,” philosophical naturalism commits itself a priori to no particular ontological categories and to no ultimate categories at all. For the philosophical naturalist, ontological categories are not a priori primitives but a posteriori derivatives of scientific theories and common human experience. As such, the ontological categories of philosophical naturalism are not scientifically restrictive, meaning, very importantly, that they are subject to any adjustments to which scientific theories are subject and can be altered as scientific understanding changes.

It is clear that the ontology of philosophical naturalism is itself theoretical in the scientific sense: it is an explanation, albeit much more general than a scientific one, of what is warranted as knowledge, why we do not have certain other kinds of “knowledge,” and why we therefore cannot lay cognitive claim to ontological categories such as the supernatural. It is not a categorical rejection of the supernatural but a constantly tentative rejection of it in light of the heretofore consistent lack of confirmation of it. And rather than accepting methodological naturalism a priori as the only reliable methodology for acquiring knowledge about the cosmos, it accepts it rather as a methodology the reliability of which has been established historically by its success and the absence of any successful alternative method for acquiring knowledge about either the natural world or a supernatural order. The general rule for philosophical naturalism is this: The more of the cosmos that science is able to explain, the less warrant there is for explanations that include a divine or transcendent principle as a causal factor.

For the philosophical naturalist, the rejection of supernaturalism is a case of “death by a thousand cuts.” Since its inception, methodological naturalism has consistently chipped away at the plausibility of the existential claims made by supernaturalism by providing increasingly successful explanations of aspects of the world that religion has historically sought to explain, such as human origins. The threat faced by supernaturalism is not the threat of logical disproof but the fact of having its explanations supplanted by scientific ones.

Paul Kurtz correctly perceived the implications of methodological naturalism in evolutionary biology, namely, the implications of the fact that the methods of studying humans are fundamentally the same as those of studying the rest of the natural world: the more knowledge of human biological existence yielded by the reliance upon methodological naturalism, the less need or justification for supernatural explanations. Kurtz wrote, “The new critics of Darwinism properly perceive that, if the implications of Darwinism are fully accepted, this would indeed mean a basic change in the outlook of who we are.”19 This is because modern evolutionary biology is the product of Darwin and his successors’ exclusive reliance upon methodological naturalism. Indeed, the problem for nonnaturalist philosophies is that science, with its historical track record of explanatory success, has progressively crowded out nonnaturalist explanations of the cosmos. This expansion and confirmation of scientific knowledge, combined with the absence of any other reliable methodology, results in the increasing marginalization of nonnaturalistic worldviews.

The gaps in scientific knowledge that have historically functioned as entry points for divine creativity are considerably narrower than they were just a generation ago. Every expansion in scientific knowledge has left in its wake a more-shrunken space of possibilities from which to infer the plausibility of supernaturalism. Science is yielding an increasingly expansive and supportable picture of continuity between humans and other life-forms and between living organisms and the rest of the cosmos from whose elements, such as the carbon produced during the evolution of stars, these organisms are constituted. The more expansive the continuity, the firmer the foundation for the inference from methodological naturalism to philosophical naturalism and the less plausible the nonnaturalistic explanations.

Since philosophical naturalism is an outgrowth of methodological naturalism and methodological naturalism has been validated by its epistemological and technological success, every expansion in scientific understanding lends it further confirmation. For example, should life be genuinely created in the laboratory from the nonorganic elements that presently compose living organisms, this discovery would add tremendous weight to philosophical naturalism. Should cognitive science and neurobiology succeed conclusively in explaining the phenomenon of human consciousness, mind-body dualism would be completely undermined, and philosophical naturalism would again be immeasurably strengthened.20

For philosophical naturalism, this is better than logical entailment, which would make it the only permissible conclusion of methodological naturalism. Relationships of logical necessity need not reflect any state of affairs in the world, whereas expansions of empirically verifiable knowledge always do. The known world expands, and the world of impenetrable mystery shrinks. With every expansion, something is explained that at an earlier point in history had been permanently consigned to supernatural mystery or metaphysical speculation. And the expansion of scientific knowledge has been and remains an epistemological threat to any claims that have been fashioned independently (or in defiance) of such knowledge.

One reason that belief in the supernatural remains widespread, despite its negligibility, is that, as discussed earlier, it cannot be proven wrong, and the epistemological insulation provided by its inaccessibility is accorded the weight of evidence despite the fact that it carries no evidential weight at all. It is not susceptible to confirmation or disconfirmation on the basis of evidence. Supernaturalism must be confirmed with unequivocal empirical evidence, and such confirmation would only demonstrate that this newly verified aspect of reality had all along never been supernatural at all but rather a natural phenomenon that just awaited an appropriate scientific test. Supernaturalists have not succeeded in providing such a test, but the naturalist has all the time in the world—and is prepared to give the supernaturalist all the time in the world—to make the attempt. In the meantime, the philosophical naturalist can point to the constantly expanding success of science in explaining what once were thought intractable mysteries or fixed categories of experience and reality.

To say that we live in a natural world, situated in a universe governed by natural laws, even if these laws are considered nothing more than invariable regularities, is to say a great deal, the major points of which are specified by Kurtz: “Today, it is possible to defend . . . naturalism . . . on empirical scientific grounds. Naturalism thus provides a cosmic interpretation of nature. The universe is basically physical-chemical or material in structure, it is evolving in time; human life is continuous with other natural processes and can be explained in terms of them. To defend naturalism today is to say something significant, for it is an alternative to supernaturalism, . . . [which] is unsupported by scientific evidence.”21

Science, because of its reliance upon methodological naturalism, lends no support to belief in the supernatural. Consequently, philosophical naturalism, because of its own grounding in methodological naturalism, has no room for it either. While for the supernaturalist this absence may be the chief complaint against both science and methodological naturalism, for the philosophical naturalist, it is the source of the greatest confidence in both.

Editor’s Note: This article was adapted with permission from one published in Philo, Vol. 3, No. 2 (Fall-Winter 2000).



  1. See Robert Pennock, Tower of Babel: The Evidence Against the New Creationism, Chapter 4, “Of Naturalism and Necessity” (Cambridge, Massachusetts: The MIT Press, 1999), 181–214.
  2. In this article, I shall use the term philosophical naturalism instead of metaphysica
    or ontological naturalism, although all three are synonymous and may be understood in every use of the former term.
  3. Paul Kurtz, “Darwin Re-Crucified: Why Are So Many Afraid of Naturalism?,” Free Inquiry, Spring 1998, 17. Kurtz also de ned a third, ethical sense of naturalism, which falls outside the concern of this article.
  4. Sidney Hook, “Natulaism and First Principals,” in The Quest For Being, ed. Sidney Hook, (Buffalo, N.Y.: Prometheus Books, 1991), 185–86
  5. Hilary Kornblith, “Naturalism: Both Metaphysical and Epistemological,” in Philosophical Naturalism, ed. Peter A. French, Theodore E. Uehling Jr., and Howard K. Wettstein, vol. 19, Midwest Studies in Philosophy (Notre Dame, Ind.: University of Notre Dame Press, 1994), 50.
  6. E.O. Wilson, On Human Nature (Cambridge, Mass.: Harvard University Press, 1978), 192; quoted in Arthur N. Strahler, Understanding Science: An Introduction to Concepts and Issues (Buffalo, N.Y.: Prometheus Books), 339. For a similar, more recent statement on the possibility of explaining religion naturalistically, see E. O. Wilson, Consilience: The Unity of Knowledge, Chapter 11, “Ethics and Religion” (New York: Alfred A. Knopf, 1998).
  7. Steven Schafersman, “Naturalism and Materialism,” in “Naturalism Is an Essential Part of Science”; /
  8. Schafersman, “What Is Science?,” in “Naturalism Is an Essential Part of Science.”
  9. “The burden of proof rests entirely upon those who assert that there exists another kind of knowledge over and above technological, common sense, empirical knowledge, and the scienti c knowledge which is an outgrowth and development of it.” Hook, “Scientific Knowledge and Philosophic ‘Knowledge,’” in The Quest for Being, 217.
  10. Hook, “Naturalism and First Principles,” in The Quest for Being, 173–74.
  11. Sidney Hook, “For an Open Minded Naturalism,” Southern Journal of Philosophy 13, no. 1 (Spring 1975), 132.
  12. Ibid., 130.
  13. Ibid., 131–32.
  14. Hook, “Religion and the Intellectuals,” in The Quest for Being, 97.
  15. “Existential import” is de ned as “the commitment to the existence of certain objects that is entailed by a given proposition.” Baruch A. Brody, “Glossary of Logical Terms,” in The Encyclopedia of Philosophy, 1967 ed.
  16. Hook, “Naturalism and First Principles,” in The Quest for Being, 177.
  17. Hook, “Scientific Knowledge and Philosophical ‘Knowledge,’” in The Quest for Being, 214.
  18. Kornblith, “Naturalism: Both Metaphysical and Epistemological,” 40.
  19. Kurtz, “Darwin Re-Crucified,” 17.
  20. Science is proceeding incrementally toward these goals. According to Daniel C. Dennett, materialism is already the accepted point of view in the explanation of mind: “The prevailing wisdom, variously expressed and argued for, is materialism: there is only one sort of stuff, namely matter—the physical stuff of physics, chemistry, and physiology—and the mind is somehow nothing but a physical phenomenon.” Daniel C. Dennett, Consciousness Explained (Boston: Little, Brown and Company, 1991), 33.
  21. Kurtz, “Darwin Re-Crucified,” 17.

Barbara Forrest

Barbara Forrest is professor of philosophy at Southeastern Louisiana University and coauthor of Creationism’s Trojan Horse: The Wedge of Intelligent Design (with Paul R. Gross, Oxford University Press, 2004, 2007). She was a key expert witness in the 2005 case of Kitzmiller v. Dover Area School District and has served on the boards of the National Center for Science Education, American United for the Separation of Church and State, and the New Orleans Secular Humanist Association.

During the past two decades, an attack has been waged in the United States against both methodological naturalism and philosophical naturalism.

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