Philosophical naturalism has been described in various ways. In its broadest and strongest sense, naturalism is the metaphysical position that "nature is all there is and all basic truths are truths of nature."[1] This is generally referred to as metaphysical or ontological naturalism. Another basic form, called methodological naturalism, is the epistemology and methodological principle which forms the foundation for the scientific method. It requires that scientific hypotheses are explained and tested by reference to natural causes and events.[2] Yet another form of naturalism is the idea that the methods of science should be used in philosophy. Science and philosophy, according to this view, are said to form a continuum and, hence, the same methods apply to both. W.V. Quine, George Santayana, and others have advocated this view. Any method of inquiry or investigation or any procedure for gaining knowledge that limits itself to natural, physical, and material approaches and explanations can be described as naturalistic.
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Many modern philosophers of science[3] use the terms methodological naturalism or scientific naturalism to refer to the methodological assumption that explanations of observable effects are practical and useful only when they hypothesize natural causes (i.e., specific mechanisms, not indeterminate miracles). In other words, methodological naturalism is the view that the scientific method (hypothesize, predict, test, and repeat) is the only effective way to investigate reality.
Methodological naturalism can be contrasted with metaphysical naturalism or ontological naturalism, which refers to the metaphysical belief that the natural world (i.e. the universe) is all that exists and, therefore, nothing supernatural exists. In metaphysical naturalism's paradigm observable events in nature are explainable only by natural causes.
This distinction between the two types of naturalism is made by philosophers supporting science and evolution in the creation–evolution controversy to counter the tendency of some proponents of Creationism or intelligent design to refer to 'methodological naturalism' as 'scientific materialism' or as 'methodological materialism' and conflate it with 'metaphysical naturalism'.[2] These proponents of creationism use this assertion to support their claim that modern science is atheistic, and contrast it with their preferred approach of a revived natural philosophy which welcomes supernatural explanations for natural phenomena and supports theistic science.
The ideas and assumptions of philosophical naturalism were first seen in the works of the Ionian pre-Socratic philosophers. Particularly Thales, the man considered to be the father of science, as he was the first to give explanations of natural events without the use of supernatural causes. Jonathan Barnes's introduction to Early Greek Philosophy (Penguin) describes these early philosophers as subscribing to principles of empirical investigation that strikingly anticipate naturalism.
But the modern emphasis in methodological naturalism can be traced back more directly to the ideas of medieval scholastic thinkers during the Renaissance of the 12th century:
Isaac Newton, when asked about the lack of mention of God in his works on physics, is said to have replied, "Hypotheses non fingo." ("I do not make hypotheses.") Similarly, Pierre Simon de Laplace, when asked about the lack of mention of God in his work on celestial mechanics, is said to have replied, "I have no need of that hypothesis."
During the Enlightenment, a number of philosophers including Francis Bacon and Voltaire outlined the philosophical justifications for removing appeal to supernatural forces from investigation of the natural world. Subsequent scientific revolutions would offer modes of explanation not inherently theistic for biology, geology, physics, and other natural sciences.
The term "methodological naturalism" for this approach is much more recent. According to Ronald Numbers, it was coined in 1983 by Paul de Vries, a Wheaton College philosopher. De Vries distinguished between what he called "methodological naturalism," a disciplinary method that says nothing about God's existence, and "metaphysical naturalism," which "denies the existence of a transcendent God."[5] The term "methodological naturalism" had been used in 1937 by Edgar Sheffield Brightman in an article in The Philosophical Review as a contrast to "naturalism" in general, but there the idea was not really developed to its more recent distinctions.[6]
In a series of articles and books from 1996 onwards, Robert T. Pennock wrote using the term methodological naturalism to clarify that the scientific method confines itself to natural explanations without assuming the existence or non-existence of the supernatural, and is not based on dogmatic metaphysical naturalism as claimed by creationists and proponents of intelligent design, in particular Phillip E. Johnson. Pennock's testimony as an expert witness[7] at the Kitzmiller v. Dover Area School District trial was cited by the Judge in his Memorandum Opinion concluding that "Methodological naturalism is a "ground rule" of science today"[8]
Apart from the creationist claims, the historical support of methodological naturalism by Christians is noted by Numbers:
W. V. Quine describes naturalism as the position that there is no higher tribunal for truth than natural science itself. There is no better method than the scientific method for judging the claims of science, and there is neither any need or any place for a "first philosophy", such as (abstract) metaphysics or epistemology, that could stand behind and justify science or the scientific method.
Therefore, philosophy should feel free to make use of the findings of scientists in its own pursuit, while also feeling free to offer criticism when those claims are ungrounded, confused, or inconsistent. In this way philosophy becomes "continuous with" science. Naturalism is not a dogmatic belief that the modern view of science is entirely correct. Instead, it simply holds that science is the best way to explore the processes of the universe and that those processes are what modern science is striving to understand.
Karl Popper equated naturalism with inductive theory of science. He rejected it based on his general critique of induction (see problem of induction), yet acknowledged its utility as means for inventing conjectures.
A naturalistic methodology (sometimes called an "inductive theory of science") has its value, no doubt. […] I reject the naturalistic view: It is uncritical. Its upholders fail to notice that whenever they believe to have discovered a fact, they have only proposed a convention. Hence the convention is liable to turn into a dogma. This criticism of the naturalistic view applies not only to its criterion of meaning, but also to its idea of science, and consequently to its idea of empirical method.
– Karl R. Popper, The Logic of Scientific Discovery (Routledge, 2002), pp. 52-53, ISBN 0-415-27844-9.
Popper instead proposed the criterion of falsifiability for demarcation.
Contemporary philosopher Alvin Plantinga has argued that evolutionary naturalism is incoherent. In Science and Theology News he attacks the conclusions of the Kitzmiller trial and suggests that the term "science" denotes any activity that is:
He concludes "if you exclude the supernatural from science, then if the world or some phenomena within it are supernaturally caused – as most of the world's people believe – you won't be able to reach that truth scientifically."
Metaphysical naturalism, which is often called "philosophical naturalism" or "ontological naturalism", takes an ontological approach to naturalism. Ontology is a branch of metaphysics that studies being, and so this is the view that the supernatural does not exist, thus entailing strong atheism.
Steven D. Schafersman contends methodological naturalism is "the adoption or assumption of philosophical naturalism within scientific method with or without fully accepting or believing it … science is not metaphysical and does not depend on the ultimate truth of any metaphysics for its success (although science does have metaphysical implications), but methodological naturalism must be adopted as a strategy or working hypothesis for science to succeed. We may therefore be agnostic about the ultimate truth of naturalism, but must nevertheless adopt it and investigate nature as if nature is all that there is." [10]
This definition rules out recourse to the supernatural. Pennock contends[11] that as supernatural agents and powers "are above and beyond the natural world and its agents and powers" and "are not constrained by natural laws", only logical impossibilities constrain what a supernatural agent could not do, and "If we could apply natural knowledge to understand supernatural powers, then, by definition, they would not be supernatural". As the supernatural is necessarily a mystery to us, it can provide no grounds on which to judge scientific models. "Experimentation requires observation and control of the variables … But by definition we have no control over supernatural entities or forces." Allowing science to appeal to untestable supernatural powers would make the scientist's task meaningless, undermining the discipline that allows science to make progress, and "would be as profoundly unsatisfying as the ancient Greek playwright's reliance upon the deus ex machina to extract his hero from a difficult predicament."
Naturalism of this sort says nothing about the existence or nonexistence of the supernatural which by this definition is beyond natural testing. Other philosophers of science hold that some supernatural explanations might be testable in principle, but are so unlikely, given past results, that resources should not be wasted exploring them. Either way, their rejection is only a practical matter, so it is possible to be a methodological naturalist and an ontological supernaturalist at the same time. For example, while natural scientists follow methodological naturalism in their scientific work, they may also believe in God (ontological supernaturalism), or they may be metaphysical naturalists and therefore atheists. This position does not preclude knowledge that derives from the study of what is hitherto considered supernatural, but considers that if such a phenomenon can be scientifically examined and explained naturally, it, then, by definition, ceases to be supernatural.
Supporters of creationism claim that the possibility of supernatural action is unnecessarily excluded by the current practices and theories of science. Currently, proponents of intelligent design argue that the naturalist conception of reality is not needed in order to do science. Their general criticism is that insisting that the natural world is a closed system of inviolable laws independent of theism or supernatural intervention will cause science to come to incorrect conclusions and inappropriately exclude research that claims to include such ideas.[12]
The subject was given detailed attention during the Kitzmiller v. Dover Area School District trial in 2005, and in his memorandum of findings[8] United States federal court judge John E. Jones III concluded that "Methodological naturalism is a 'ground rule' of science today." This ruling sets a federal district judicial precedent in the context of legal restrictions on the teaching of religion in U.S. schools, and more broadly the memorandum sets out an assessment of the evidence and arguments relating to the use in science of methodological naturalism as against supernatural explanations.