Many simply refuse to consider the design hypothesis on the grounds that it does not qualify as “scientific.” Such critics affirm an extraevidential principle known as “methodological naturalism”. Methodological naturalism (MN) asserts that for a hypothesis, theory, or explanation to qualify as “scientific” it must invoke only naturalistic or materialistic causes. Clearly, on this definition, the design hypothesis does not qualify as “scientific”. Yet, even if one grants this definition, it does not follow that some nonscientific (as defined by MN) or metaphysical hypothesis may not constitute a better, more causally adequate, explanation. Whatever its classification, the design hypothesis does constitute a better explanation than its naturalistic rivals for the origin of specified complexity in both physics and biology. Surely, simply classifying this argument as metaphysical does not refute it.
— Stephen Meyer, from Science and Evidence for Design in the Universe, p. 99