Another excellent bit from Overcoming Bias:
Of course this plays right into the creationist claim that Intelligent Design isn’t getting a fair shake from science – that science has prejudged the issue in favor of atheism, regardless of the evidence. If science excluded Intelligent Design a priori, this would be a justified complaint!
But let’s back up a moment. The one comes to you and says: “Intelligent Design is excluded from being science a priori, because it is ‘supernatural’, and science only deals in ‘natural’ explanations.”
What exactly do they mean, “supernatural”? Is any explanation invented by someone with the last name “Cohen” a supernatural one? If we’re going to summarily kick a set of hypotheses out of science, what is it that we’re supposed to exclude?
By far the best definition I’ve ever heard of the supernatural is Richard Carrier’s: A “supernatural” explanation appeals to ontologically basic mental things, mental entities that cannot be reduced to nonmental entities.
This is the difference, for example, between saying that water rolls downhill because it wants to be lower, and setting forth differential equations that claim to describe only motions, not desires. It’s the difference between saying that a tree puts forth leaves because of a tree spirit, versus examining plant biochemistry.