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Methodological naturalism

Methodological naturalism (MN) is the philosophical tenet that, within scientific enquiry, one can only use naturalistic explanation - i.e. one's explanations must not make reference to the existence of supernatural forces and entities. Note that methodological naturalism does not hold that such entities or forces do not exist, but merely that one cannot use them within a scientific explanation. Methodological naturalism is often considered to be an implied working rule of all scientific research and logically entails neither philosophical naturalism nor atheism, though some would argue that it implies such a connection.

Specifically, the status of methodological naturalism within scientific enquiry has been challenged by Phillip E. Johnson, a now-retired professor of law (at Boalt Hall at the University of California, Berkeley) who has in a number of works (Darwin on Trial, Defeating Darwinism, Objections Sustained, and The Wedge of Truth) argued that methodological naturalism is a prop used by the Darwinian orthodoxy to ensure the exclusion of evidence for Intelligent Design Theory on a priori grounds. Johnson argues that a strong commitment to methodological naturalism on a priori grounds can blind researchers to the truth just as easily as a commitment to a literal reading of Joshua blinded the church to the evidence for Copernicus's heliocentric theory.

Johnson's position has been rejected by some scholars, like Robert Pennock who in his Tower of Babel notes that he often conflates methodological naturalism with philosophical naturalism. However, others note that the objection Pennock raises ignores the main thrust of Johnson's argument that a methodological assumption that excludes the possibility of looking at the evidence for a theory inevitably leads to a rejection of that theory.

Though many evolutionary biologists continue to reject Johnson's argument, it has been noted that Richard Lewontin who has debated Johnson several times on the issue, seems to have adjusted his position to one which is compatible with Johnson's view. In a recent review of a book by Carl Sagan, Lewontin argued that true science requires a prior commitment to both methodological and philosophical naturalism:

Our willingness to accept scientific claims that are against common sense is the key to an understanding of the real struggle between science and the supernatural. We take the side of science in spite of its failure to fulfill many of its extravagant promises of health and life, in spite of the tolerance of the scientific community of unsubstantiated just?so stories, because we have a prior commitment, a commitment to materialism. It is not that the methods and institutions of science somehow compel us to accept a material explanation of the phenomenal world, but on the contrary, that we are forced by our a priori adherence to material causes to create an apparatus of investigation and a set of concepts that produce material explanations, no matter how counterintuitive, no matter how mystifying to the uninitiated. Moreover, that materialism is absolute, for we cannot allow a Divine Foot in the door.

In this context it is important to note that Lewontin seems to have changed his mind, in order to agree with Johnson's claim that evolutionary theory is based on an absolute or philosophical naturalism. However, it is also important to note that Lewontin's statement does not amount to a wholesale acceptance of Johnson's project, since Johnson is defending the right of the advocates of intelligent design theory to have their case evaluated on the merits of the current evidence, while Lewontin is claiming that rigorous scientific methodology requires an absolute commitment to natualism which rules out such evidence on a priori grounds. It is also important to note that this quotation from Lewontin, which makes its way time and time again into creationist propaganda, is Johnson's attack on MN has wider implications than just for the sciences; in Reason in the Balance (199x), he attacked naturalism in law.

Who is a leading defender of MN in the scientific community?

MN is not usually articulated explicitly; scientists tacitly assume that supernatural forces needn't be taken into account.

Is there any more history to this?
The term MN itself probably doesn't go much past the 1980s; Johnson acknowledges taking it (or "methodological atheism") from Nancey Murphy, a theologian with training in the philosophy of science. Arguably, MN itself goes back to the Ionian pre-Socratic philosophers of the 4th c. BCE; see, e.g., Jonathan Barnes's introduction to Early Greek Philosophy (Penguin), which describes them as subscribing to principles of empirical investigation that strikingly anticipate MN. Benjamin Wiker traces the historical development of the modern materialist perspective starting with the choice of the Epicureans to focus exclusively on the natural realm as a necessary step toward their goals; see his book "Moral Darwinism; How We Became Hedonists".