As defined by philosopher Paul Draper, naturalism is "the hypothesis that the physical world is a 'closed system' in the sense that nothing that is neither a part nor a product of it can affect it." More simply, it is the denial of the existence of supernatural causes. In rejecting the reality of supernatural events, forces, or entities, naturalism is the antithesis of supernaturalism.
As a substantial view about the nature of reality, it is often called metaphysical naturalism, philosophical naturalism, or ontological naturalism to distinguish it from a related methodological principle. Methodological naturalism, by contrast, is the principle that science and history should presume that all causes are natural causes solely for the purpose of promoting successful investigation. The idea behind this principle is that natural causes can be investigated directly through scientific method, whereas supernatural causes cannot, and hence presuming that an event has a supernatural cause for methodological purposes halts further investigation. For instance, if a disease is caused by microbes, we can learn more about how microbes interact with the body and how the immune system can be activated to destroy them, or how the transmission of microbes can be contained. But if a disease is caused by demons, we can learn nothing more about how to stop it, as demons are said to be supernatural beings unconstrained by the laws of nature (unlike natural causes).
In utilizing methodological naturalism, science and history do not assume a priori that, as a matter of fact, supernatural causes don't really exist. There is no conceptual conflict between practicing science or history and believing in the supernatural. However, as several of our authors argue below (e.g., Augustine, Forrest, and Oppy), methodological naturalism would not be as stunningly successful as it has in fact been if metaphysical naturalism were false. Thus the de facto success of methodological naturalism provides strong empirical evidence that metaphysical naturalism is probably true.
Letter on Reformation
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