Hokum-Balderdash Assay

Skeptico asks, "Why does science exclude the supernatural?" As he rightly points out one very important reason is the nontestable/nonfalsifiable character of supernatural claims. We have already heard philosopher Barbara Forrest comment on this matter:

Any claim that depends on the supernatural ... is not falsifiable. [I]n science whatever claim you make has to be grounded in empirical evidence and you have to at least in principle know what kind of disconfirmation would show your theory to be wrong.... And so any position that's grounded in faith and the supernatural is one that by definition not falsifiable.

Geologist Arthur Strahler explains why the supernatural is outside the purview of science:

Religious tenets, which usually involve belief in supernatural entities, are ... beyond the limits of scientific appraisal.

[S]upernatural forces, if they can be said to exist, cannot be observed, measured, or recorded by the procedures of science--that's simply what the word "supernatural" means. There can be no limit to the kinds and shapes of supernatural forces and forms the human mind is capable of conjuring up "from nowhere." Scientists therefore have no alternative but to ignore the claims of the existence of supernatural forces and causes. This exclusion is a basic position that must be stoutly adhered to by scientists or their entire system of evaluating and processing information will collapse. (Arthur N. Strahler, Understanding Science: An Introduction to Concepts and Issues, Buffalo, NY: Prometheus Books, 1992, p. 13-14)

To get technical about it, science must exclude the supernatural because at its very foundation "science is committed to methodological naturalism (MN)," a position which "does not deny the existence of supernatural entities per se" but "simply assumes for the purpose of inquiry that they do not exist." In the same essay philosopher Michael Martin concludes that science's commitment to MN is warranted because it does not block inquiry, it is not a science-stopper unlike supernatural explanations. (Justifying Methodological Naturalism) 

Coincidentally, Unscrewing the Inscrutable has cogent things to say about MN:

The reason that scientists use MN when they are performing science is quite simply because it works. MN assumes that the natural world is all there is, then observes it and constructs hypotheses and theories that attempt to describe how a given naturally-observed phenomenon works. This is not to say that since MN presupposes a natural world, that there is no supernatural world. The question of whether or not a supernatural world exists just isn't ever addressed by MN. It can't be. That's why it's called "methodological naturalism" and not "methodological supernaturalism".