A recent philosophical discovery has invalidated all theories that invoke the supernatural. People for millennia have proposed supernatural theories to explain myriad aspects of the world around them, but then David Deutsch discovered the philosophical principle of good explanation. This principle asserts that a good explanation is “hard to vary while still accounting for what it purports to account for”. That is, it explains something in such a way that each of its details plays a functional role in the explanation, and consequently changing any of its details would spoil its explanatory power. If an explanation can be varied without diminishing its explanatory power, then it is a “bad” explanation—because it is not in fact a single explanation, but is instead a set of mutually exclusive variant explanations, which cannot be distinguished from each other using rational criteria. Deutsch’s principle of good explanation invalidates all theories that invoke the supernatural, because the details of such explanations are unconstrained by nature, and so are infinitely variable.