Contrary to proponents’ claims, methodological naturalism is not metaphysically neutral. Consequently, its acceptance as a practice requires justification. Unfortunately for its advocates, attempts to justify it are failures. It cannot be defended as a definition, or a self-imposed limitation, of science, nor, more modestly, as an inductively justified commitment to natural causes. As a practice, it functions not to further scientific investigation, but rather to impose an explanatory straitjacket.