Naturalism and Science
Naturalism is a worldview that relies upon experience, reason, and science to develop an understanding of reality and humanity's place within reality. Naturalism is hence a worldview that is heavily dependent on science for knowledge about reality. One's attitude towards science and scientific Method will therefore control how one thinks about naturalism.
Nowadays two versions of naturalism are frequently contrasted: methodological naturalism and ontological naturalism. Definitions of these two versions usually sound like this. Methodological naturalism holds that the only sort of knowledge available to us is the knowledge learned by applying the scientific method to all hypotheses. On this view, the scientific method itself suffices to weed out non-natural hypotheses as unscientific, by requiring hypotheses to be consistent with suitably naturalistic principles (no mysterious causes, no miracles, no violation of causal closure or conservation of energy, etc.). Such requirements, while guaranteeing the screening out on the non-natural, presupposes some basic understanding of what the natural consists of. Where could that understanding come from? Only from some already established knowledge about nature. This leads the naturalist to Ontological Naturalism, which holds that reality only consists of those things recognized by an exemplary science, such as physics, which has been satisfactorily tested by scientific method. Have you noticed yet that methodological and ontological naturalism depend on each other for substantive content? They cannot be defined independently of each other, since methodology by itself will consider any hypothesis for testing without prejudice, and ontology by itself is sheer dogmatism without a standard of knowledge. The putative contrast between methodological naturalism and ontological naturalism is spurious -- they work together or not at all. They can have a virtuous relationship by mutually enlarging each other as science progresses -- new scientific knowledge often arrives with improved methodology, which in turn extends the reach of scientific inquiry, which leads to more new knowledge, etc. You can read more about methodological and ontological naturalism in the article "Naturalism".
The label of Metaphysical Naturalism is sometimes applies to the broadest definition of naturalism (see for example wikipedia's "Metaphysical Naturalism"). Furthermore, the labels of Physicalism and Materialism are sometimes used by philosophers as synonyms for naturalism (you can read about "Physicalism" here). However, only some varieties of naturalism rely only on physics or the notion of matter, and naturalisms frequently have contentious relationships with metaphysics, so it is best to let Philosophical Naturalism stand for the broadest statement of naturalism.
Accordingly we shall persist with the definition of philosophical naturalism given at Naturalisms.org, which combines a methodological and ontological component: "Naturalism is a worldview that relies upon experience, reason, and science to develop an understanding of reality and humanity's place within reality."
Now that the genus of naturalism has been defined, what are the dominant species? We will proceed through five stages of discriminating significant kinds of naturalism. The conclusion of these stages identifies the seven viable varieties of naturalism. Which of these viable varieties enjoy superior status as the two major competitors in the race for recognition as the "genuine" naturalism? Read the concluding six stage!
Stage One: Science, Knowledge, and Reality
There are six primary options when considering whether science yields knowledge about reality:
Each of these six options present pathways to many different worldviews. Options 4, 5, and 6 lead to varieties of naturalism. To become a worldview, each option must provide a justification for preferring it over the rest. Examples of such justifications are added below:
Options 4, 5, and 6 can lead towards varieties of naturalism, but unless option 3B Scientific Anti-Realismis ruled out, naturalism remains hypothetical. You can proceed to another website on Scientific Realism.
Only three of the 6 primary worldviews can lead to kinds of naturalism. They are:
Each of these three major worldviews about science leads to three significant kinds of naturalism: Synoptic Monism, Perspectival Realism, and Scientific Exclusivism. Transcendent realism may be ignored here because any transcendent natural reality, if it exists, cannot be the subject of the contest between naturalism and non-naturalism. Current scientific exclusivism may also be ignored here because the scientific exclusivist, when challenged over something that current science can't yet explain, will resort to the claim that future science will explain it.
Stage One: Three Kinds of Naturalism
Stage Two: Explaining Experiences using Science's Theories
Let us further consider ways of distinguishing kinds of naturalism. Consider these three kinds of naturalisms.
Narrow Naturalism: If some X is among those things (or among the properties of those things) which are described by science's best theories, then the existence of X is accepted; otherwise, its existence must be denied.
Fitting Naturalism: All the entities accepted by narrow naturalism exist, plus additional things as follows: If some X is successfully hypothesized as really being a Y that is among those things (or among the properties of those things) which are described by science's best theories, then the existence of X may be accepted.
Broad Naturalism: All the entities accepted by fitting naturalism exist, plus additional things as follows: If some X is successfully explained by a hypothesis about why X exists which references only those things (or properties of those things) which are described by science's best theories, then the existence of X may be accepted.
It must be made clear that in these definitions, we mean by "those things" any entities which are used by scientific theories -- from "things" in the substantive sense of material bodies, and also energies, forces, laws, and the like. Naturalists can disagree among themselves about the types of entities that are attributed existence by scientific theories (for example, do laws of nature really exist in the same way that atoms exist, or do numbers exist because science uses measured quantities, etc.). These disagreements are not relevant to the categorization of naturalisms discussed here.
Let's apply the distinction between these three naturalisms to the experience of colors. The narrow naturalist is tempted to reject the existence of colors, because no color is found among the basic properties of those things described by science's best theories. If the narrow naturalist is narrow in an additional sense because she considers physics as supplying the best scientific theories, then this naturalist will reject the existence of colors because color is not a property of any atomic or subatomic particle, or of any force of nature. The fitting naturalist can accept the existence of colors if an adequate hypothesis find a fitting place in nature for colors. For example, a successful hypothesis that a color really is the "surface spectral reflectance" from an object would permit the fitting naturalist to accept that colors naturally exist. The broad naturalist only asks that some adequate hypothesis, which uses terms from science's best theories, explains why colors are experienced. For example, a successful hypothesis that explains how colors are seen whenever sufficient visible light in certain wavelengths stimulates the optic systems of normally functioning human brains would permit the broad naturalist to accept that colors naturally exist. In summary, the narrow naturalist wants to eliminate colors from nature by comparing them against science's theories, the fitting naturalist wants to fit colors into the natural world by reducing them to scientific things, and the broad naturalist wants liberal flexibility to accept colors by explaining how colors are naturally experienced.
So far we have distinguished six kinds of naturalism, along two dimensions: (1) the degree of ontological confidence given to science, from Synoptic monism to perspectival realism to scientific exclusivism; and (2) the breadth of explanatory discretion given to science, from narrow to fitting to broad naturalism.
Stage Two: Three More Kinds of Naturalism
Stage Three: How Many Sciences Describe Reality?
There is one more dimension that further distinguishes kinds of naturalisms: (3) the number of scientific fields permitted to describe reality. Some naturalists are happy with letting many sciences know reality, while other naturalists want only one scientific field to know reality. The latter type of naturalists have typically accepted a methodological principle that may be called "reductionist universalism" -- only the smallest parts of reality really exist, and the natural laws about those parts are universally valid (they hold in all regions of the universe), exclusively valid (no other laws have independent validity), and exhaustively valid (all events are dictated by these laws). As physics is the scientific field that knows the smallest parts of reality, reductionist universalism amounts to the claim that all of reality ultimately consists solely of subatomic particles and that all events in the natural universe are ultimately dictated by the laws those subatomic particles obey. The program of reductionism amounts to the claim that any complex thing should be analyzed down into its components, and each of these components must in turn be analyzed further, etc., until the ultimate smallest parts (those studies by subatomic physics) are identified and their interact laws are discovered. Theoretical reductions to physics are therefore a series of analyses, from higher complex levels of nature to lower simple levels of nature, until the lowest (smallest) level is reached, and this series of analyses explains how the behavior of any complex thing is fully explained by the interactive behaviors of the smallest parts. If, according to reductionist universalism, subatomic particles have ontological priority and their laws have explanatory priority, then physics has naturalistic priority. The sciences could be unified in this way into physics alone. You can read more about the history of "Atomism", "Reduction", and the "Unity of Science" movement. The naturalist who follows reductionist universalism will be the sort of materialist who puts physics first -- this naturalism is "physicalism."
Other kinds of naturalism do not agree with reductionist universalism and feel comfortable with permitting other scientific fields to describe reality with just as much legitimacy as physics. Because the biological and social sciences have traditionally used some methodological principles and modes of causality that depart from the physical sciences, many naturalists want to draw a line between trustworthy physical sciences (physics, chemistry, geosciences, astronomy, cosmology) and suspicious biological and social sciences. For example, some approaches to the social sciences have assumed the existence of social entities (that must not be treated as mere aggregates of people), and some biological and social sciences have use teleological causality (explanations that appeal to future outcomes to explain present behaviors). We will not discuss this internal dispute among naturalists here. However, the naturalists who would permit just the physical sciences to describe reality (let us call their view "scientism") do form a separate camp from those naturalists who are comfortable with all of the physical, biological, and social sciences describing reality (let us call their view "pluralism").
Stage Three: Three More Kinds of Naturalism
Stage Four: How Many Naturalisms?
The varieties of naturalism may be distinguished along three dimensions: (1) the degree of ontological confidence given to science, from Synoptic monism to perspectival realism to scientific exclusivism; (2) the breadth of explanatory discretion given to science, from narrow to fitting to broad naturalism; and (3) the number of scientific fields permitted to describe reality, from just physics to the physical sciences to all sciences.
If all combinations of these nine kinds of naturalism were created, then 27 varieties of naturalism would result. However, many of these 27 varieties are not viable because of coherence problems, and some are not practical because their principles would conflict. Let us consider the number of viable naturalisms by first considering the result of combining the breadth of explanatory discretion given to science with the number of scientific fields permitted to describe reality. The nine kinds of naturalism that result try to express nine different ways of formulating the explanatory function of science.
TABLE ONE: NINE KINDS OF NATURALISM
Let us next consider combining these nine kinds of naturalism, arrayed according to their formulation of the explanatory function of science, with the three kinds of naturalism that express the degree of ontological confidence given to science, from synoptic monism to perspectival realism to eliminative materialism. These combinations generate twenty-seven potential varieties of naturalism. Not all are viable, however.
TABLE TWO: TWENTY-SEVEN VARIETIES OF NATURALISM?
After eliminating 16 varieties of naturalism because they are either incoherent or impractical, 11 remain for consideration. We may first consider the 4 "poor fits" to understand why these varieties are such unstable combinations that they must mutate into a nearby variety.
Eliminative Scientism: can reality be only what the physical
sciences say? Eliminative Scientism demands that reality only
consist of those things and their properties which are described by the
physical science's best theories. The various physical sciences provide
theories appropriate to their "level" of reality that concerns them.
Subatomic physics, atomic physics, chemistry, geosciences, astronomy, and
cosmology deal with levels of nature ranging from the smallest to the
grandest scales. If permitted complete theoretical liberty, these sciences
would describe nature in diverse ways that are quite different from each
other. For example, chemistry would assert that molecules exist, while
physics would prefer to speak only of atoms (and subatomic physics renounces
both molecules and atoms for the menagerie of subatomic particles).
Eliminativism puts severe pressure on a worldview to finally decide what
really exists -- so the awkwardness of disputes between the physical
sciences over the ultimate components of reality must be resolved. During
the 20th century, the needed resolution was the adoption of the principle of
"reductionist universalism" -- only the smallest parts of reality
really exist, and the natural laws about those parts are universally and
exclusively valid. As subatomic physics is the scientific field that knows the
smallest parts of reality, reductionist universalism amounts to the claim
that all of reality ultimately consists solely of subatomic particles and
that all events in the natural universe are ultimately dictated by the laws
which those subatomic particles obey. Chemistry's molecules are just
assemblies of physics' atoms, which in turn are just assemblies of
subatomic particles. Furthermore, all laws of chemistry are in principle
reducible to just necessary implications of the laws of subatomic and atomic
physics. The awkwardness of Eliminative Scientism leads to reductionist
universalism, which in turn leads to Eliminative Physicalism.
Synoptic Scientism: why demand explanations when reality has multiple modes? Synoptic Scientism suggests that reality possesses multiple aspects that are not reducible to each other, but are explainable by the sciences. However, the purpose of adopting synopticism is to avoid having to explain everything in terms of just those things described by science's best theories. If it is possible to explain all realities in terms of the knowledge of just the physical sciences, then there is no need to postulate multiple modes of reality. If a philosopher tries to develop Synoptic Scientism, either the desire for synopticism will turn the philosopher towards Synoptic Pluralism, or the optimism about science will turn the philosopher towards Perspectival Pluralism.
Perspectival Scientism: can the physical sciences fully explain diverse experience? Perspectival Scientism suggests that reality has perspectival aspects which are experienced but not themselves directly knowable by the sciences. Could such experiences nevertheless be fully explained by just the physical sciences? For example, could all experiences be accounted for by brain neurophysiology? Perhaps, but appreciation for perspectivism typically arises from skepticism about the presumptuous notion that all experiences can be explained by just the physical sciences. If a philosopher tries to develop Perspectival Scientism, either the desire for perspectivism will turn the philosopher towards Perspectival Pluralism, or the optimism about science will turn the philosopher towards Exclusivist Liberal Pluralism.
Stage Five: The Seven Viable Varieties of Naturalism
These seven viable varieties of naturalism are distinguished from each other according to their views on (1) the degree of ontological confidence given to science, from synoptic monism to perspectival realism to scientific exclusivism; (2) the breadth of explanatory discretion given to science, from narrow to fitting to broad naturalism; and (3) the number of scientific fields permitted to describe reality, from just physics to the physical sciences to all sciences. The seven varieties are listed in order from the very restrictive to the very open assertions about what reality is like.
Eliminative Physicalism: reality only is what physics says. This variety is the most austere and rigid naturalism, restricting reality most sharply. According to Eliminative Physicalism, the only realities are those that number among those things (or among their properties) which are described by physics' best theories. This eliminativism typically accepts the principle of "reductionist universalism" -- only the smallest parts of reality really exist, and the natural laws about those parts are universally, exclusively, and exhaustively valid -- and so this variety of naturalism claims that all of reality ultimately consists solely of subatomic particles (and their properties, and their laws, etc.), and that all events in the natural universe are ultimately dictated by the laws which those subatomic particles obey. According this worldview, if it rejects the existence of some X, then any belief or judgment or knowledge claim about X is probably meaningless and strictly false. Sometimes eliminative physicalists relent from this harsh treatment, saying that discourse about many condemned Xs can still be meaningful, and "second-class" practical knowledge about these Xs may be possible. But the Eliminative Physicalist who is too generous with "second-class" knowledge risks sliding over to Exclusivist Liberal Pluralism, and is under great pressure to at least admit the superiority of Reductive Physicalism.
Reductive Physicalism: reality must be reducible to physics. This variety is almost as austere as eliminative physicalism. According to Reductive Physicalism, the only realities are those of physics' best theories, plus those additional things which can be theoretically and ontologically reduced to them. Reductive Physicalism accepts reductionist universalism, but resists collapsing into eliminative physicalism by permitting the existence of things that can have their own properties, behaviors, and laws that physics itself does not investigate. The practical difference between a reductivist and an eliminativist is that an eliminativist about some X would not seek any reductive explanation of X, since it is irrational to attempt to explain the non-existent. However, most eliminativists gain their confidence in the non-existence of X after reductivists have done their work, and most physicalists are eliminativists about some things (the paranormal, the mythical) and reductivists about other things (the biological, the social). For the reductivist, chemistry's knowledge of molecules can be legitimate, so long as chemistry accepts that its entities and laws must be in principle reducible to physics' entities and laws, even if it may be difficult or seem impossible for scientists to figure out all those reductions. A harder problem for reductivism is presented by a science like geology or biology -- the reductive physicalist likewise demands that these sciences' entities and laws be reducible in principle to those of physics. How could the laws of nature concerning plate tectonics or genetic reproduction ever be reduced to those of subatomic physics? The social scientist may also be forgiven for rebelling against this imperial demand of physics. Reductive Physicalism must demand complete submission to the principle of reductionist universalism from all other sciences, so else it must admit the superiority of Exclusivist Liberal Pluralism.
Exclusivist Liberal Physicalism: physics alone supplies explanations of all reality. This variety is attractive to naturalists who are skeptical about reducing all realities to physical realities. Exclusivist Liberal Physicalism holds that reality consists of what can be explained by physics. This variety of naturalism does not adhere to the principle of reductionist universalism, keeping it distinct from its eliminativist and reductivist cousins. Exclusivist Liberal Physicalism does maintain an analogue of reductionist universalism, which can be called "explanatory universalism," which instead declares that only the things and laws theorized by physics may be referenced when explaining reality, so that explanations of things are given solely in terms of the things recognized by physics alone. The primary difficulty that confronts Exclusivist Liberal Physicalism is causality: physically explainable but irreducible things can appear to have their own causal relationships, and so one event might be described as having two sufficient causes. Unless this causal overdetermination issue is somehow resolved, Exclusivist Liberal Physicalism is under great pressure to either collapse into Reductive Physicalism, or to go in the opposite direction and mutate towards Perspectival Pluralism.
Exclusivist Liberal Scientism: the physical sciences supply explanations of all reality. Like any middle position that tries to compromise all things, this variety is highly unstable, suffering from great pressures to resign the field in favor of its exclusivist cousins. According to Exclusivist Liberal Scientism, reality consists only of those things that are explainable by the physical sciences. But why the physical sciences? The Exclusivist Liberal Physicalist will complain that purely physical explanations must in principle prevail across all the physical sciences anyways. The Exclusivist Liberal Pluralist will complain that admitting the explanatory power of the physical sciences should be extended to all of the sciences. Even worse than competition from its cousins, this variety suffers from both of the severe difficulties confronting its cousins. Like Exclusivist Liberal Physicalism, this variety must resolve the issue of causal overdetermination, lest it admit the superiority of Reductive Physicalism. Like its other cousin, Exclusivist Liberal Pluralism, this variety must also resolve the issue of incoherence between the physical sciences, which can be handled more easily by Reductive Physicalism on the one hand, or by Perspectival Pluralism on the other.
Exclusivist Liberal Pluralism: the many sciences supply explanations of all reality. This variety is attractive to naturalists who are skeptical about reducing all realities to physical realities on the one hand, and also skeptical about any naturalistic metaphysics that permits experience to yield genuine perspectives on reality that can never be fully explained by the sciences. Exclusivist Liberal Pluralism holds that reality consists of what can be explained by the sciences. Its pluralism encourages all of the sciences to draw their own conclusions about reality. But this liberality also encourages such a diversity of conclusions about reality, and such a multiplicity of entities for theorizing, that incoherence among them will inevitably result. The only way to manage this diversity is to assign each science its own task of exploring a "level" or "aspect" of reality, so that clashing scientific theories are kept apart. For example, chemistry studies the laws peculiar to interacting molecules, while subatomic physics studies the quite different laws peculiar to subatomic particles, without worrying how these entities and laws specifically relate to each other. This tactic will pull pluralism towards perspectivism -- the view that each science's knowledge is only one valid but limited perspective on reality, and no science has a monopoly or even a priority on what really exists. Explaining this coordinated and peaceful perspectivism will require great philosophical effort that surely looks like naturalistic metaphysics, since justifying such immense coordination probably can't be the work of scientific theorizing, but instead the work of higher-order principles that are not experimentally testable. How can Exclusivist Liberal Pluralism forbid experience from having any of its own independent perspectives on reality (especially since ordinary experience is not so very different from simple scientific observation)? Exclusivist Liberal Pluralism must be burdened with showing how all experiences are in principle explainable by the sciences. Any experiences not satisfactorily explained will pressure this naturalism to mutate into Perspectival Pluralism.
Perspectival Pluralism: the many sciences indicate plural
perspectives on reality. This variety offers a middle path between
Exclusivist Liberal Pluralism's reliance on science alone and Synoptic
Pluralism's hypostatizations of multiple ways of experiencing and
knowing reality. Perspectival Pluralism finds that experience
and scientific knowledge presents multiple perspectives upon the same
reality. Perspectival Pluralism requires some sort of naturalistic metaphysics -- a metaphysical
account of reality that incorporates all experience and knowledge to construct a coherent understanding of one
single natural reality
having multiple but coordinated perspectives. This naturalist
metaphysics is not testable by ordinary experimental methods because it is designed to be maximally compatible and
coherent with all knowledge and experience from all sources. Since
experience increases and knowledge
evolves, naturalistic metaphysics must adapt to keep pace, and this
adaptability serves as its test of adequacy. Perspectival Pluralism
distinguishes itself from Exclusivist Liberal Pluralism by requiring that
the perspectives of experience do not have to be explained by the sciences,
but only by the naturalistic metaphysics. Explaining why experience cannot be
fully captured by the sciences can be accomplished, for example, by
emphasizing how scientific knowledge grows from experience, or by showing
how experience emerges from the physical world (see
Properties") that science knows, or by showing
how experience has perspectives on reality which science cannot duplicate,
or by demonstrating that experience has elements not explainable by
scientific knowledge. Coordinating experience with scientific knowledge in
one coherent system is facilitated by Perspectival Pluralism's view
that experience is not itself a kind of knowledge that competes with
scientific knowledge. If any aspect of experience does deserve status as a
kind of knowledge capable of competing with scientific knowledge, Synoptic Pluralism is preferable.
Stage Six: The Two Great Naturalisms
Each of the seven viable forms of naturalism suffer from unresolved problems requiring further intense philosophical work. Lacking resolutions to their problems so far, they are under great pressure to mutate into some other variety of naturalism. The next table diagrams the seven viable naturalisms, their most urgent issues, and the direction of pressure for mutation.
TABLE THREE: SEVEN VARIETIES OF NATURALISM AND THEIR ISSUES
As evident from the lines of pressure indicated in Table Three, two naturalisms seem to exert greater persuasive power. Because of the intense pressures of unresolved issues, most naturalisms gravitate around the two great naturalisms: Reductive Physicalism and Perspectival Pluralism. They stand opposed across a wide divide that separates the physicalists from the pluralists. The essential issue for naturalism consists of the fundamental disagreement that divides Reductive Physicalism apart from Perspectival Pluralism -- does any science's knowledge, and the reality it knows, have priority (epistemic and ontological) over all other knowledge and experience? If the answer is affirmative, then the monopoly of physics is assured and Reductive Physicalism is victorious. If the answer is negative, then the plurality of knowledge and experience is assured and Perspectival Pluralism is victorious.
The Two Great Naturalisms
copyright 2007 by John R. Shook