And I think that it is a far more important truth than anything discovered by Newton, Darwin, or Einstein. But I do not mistake it for a scientific theory. It is not a scientific theory because it is not a theory of any sort. Theories tell you how things work, and this statement tells you what happened. It is an explanation all right, but it is not a scientific explanation.
Scientific explanations appeal to theories.
They are applications of theories to particular events or types of event or phenomena. Thus I would supplement Professor Grinnell's argument for methodological naturalism. It is a commonplace in discussions like this to distinguish methodological from ontological or metaphysical naturalism. Ontological or metaphysical naturalism is the thesis that everything that exists is a natural object having only natural properties. It is obvious that metaphysical naturalism entails methodological naturalism, in the sense that anyone who accepts the former is committed to the latter-one does not construct theories or explanations that appeal to things that one firmly believes not to exist.