are claimed to be the result of a bias within science toward philosophical naturalism, which is equated by many creationists with atheism. In countering this claim, philosophers of science use the term methodological naturalism to refer to the long-standing convention in science of the scientific method. The methodological assumption is that observable events in nature are explained only by natural causes, without assuming the existence or non-existence of the supernatural, and therefore supernatural explanations for such events are outside the realm of science. Creationists claim that supernatural explanations should not be excluded and that scientific work is paradigmatically close-minded. Because modern science tries to rely on the minimization of a priori assumptions, error, and subjectivity, as well as on avoidance of Baconian idols, it remains neutral on subjects such as religion or morality. Mainstream proponents accuse the creationists of conflating the two in a form of pseudoscience. Theory vs fact The argument that evolution is a theory, not a fact, has often been made against the exclusive teaching of evolution. The argument is related to a common misconception about the technical meaning of "theory" that is used by scientists. In common usage, "theory" often refers to conjectures, hypotheses, and unproven assumptions. In science, "theory" usually means "a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses." For comparison, the National Academy of Sciences defines a fact as "an observation that has been repeatedly confirmed and for all practical purposes is accepted as 'true'." It notes, however, that "truth in science ... is never final, and what is accepted as a fact today may be modified or even discarded tomorrow." Exploring this issue, paleontologist Stephen Jay Gould wrote: Marston has argued that, although the creationism argument (that because evolution is "merely" a theory, it therefore cannot also be a fact) reflects a fundamental misunderstanding of the concepts, the scientific countering of the creationist position by the simple stipulation that evolution is a fact may be counterproductive; a better approach, according to Marston, is for scientists to present evolution not as a stipulated fact but as the "best explanation" for the development of life on earth. This approach, Marston argues, is less likely to end discussion of the topic and is more readily and effectively defended, in part by reducing the burden of proof standards required for assertions of "fact" and by shifting