Methodological naturalism. Big word. Here’s what it means…
Consider the theory of gravity. An apple, unsupported by tree or table, falls. That is what it does. And it seems to do it every time. Hold an apple in the air, let go, it falls. It falls once, it falls twice, it falls a million times. And by that method, every time we test the theory of gravity, it holds. So eventually we come to the tentative conclusion: “apples will always fall”. But how can we really know that? What about the million-and-oneth time? It might behave differently if we do it one more time. It really might!
The answer is we can never know for certain.
We can boil water at sea level, a million times, and eventually conclude that water always boils at 100 degrees Celsius. And we would be wrong. It would be a theory that would eventually be proven wrong, when we eventually boil water at high altitude. The theory would have been falsified. For this reason, science works not by verifying the same experiment over and over again, but rather by attempting to disprove, over and over, and failing to do so. Find a single example that disproves a theory, and the theory has been shown to be incorrect. (Of course, there are various measures of incorrectness. Sometimes the theory can be revised and improved, sometimes it has to be scrapped.)
Now back to the apple. If, lo-and-behold, at one point we make the experiment and the apple doesn’t fall, observed under scientific conditions with no other force at play, the correct scientific conclusion is this: the theory of gravity is incorrect. This is how science works, and it works because science is practised under methodological naturalism. It is a term possibly coined by a conservative Christian to help distinguish between methodically approaching scientific experiments from a naturalistic perspective, and the philosophical stance of ontological naturalism, which states that the supernatural does not exist.
If the apple proved to float, just once, and we did not practice science from a methodological naturalistic approach, we could conclude “God has bent the rules of gravity, this once, to make the apple float”. That is all good and well, but how do we then make any scientific progress when theories do not match with predictions? Every single time a theory is proven incorrect, we could merely conclude “it is but divine intervention”.
This is no way to make progress in science, which is why science must be practised from a naturalistic perspective. Without accepting the falsification of a theory, how can we ever go about testing it? We would stick with “we’re ill because of supernatural forces”, there would be no reason to go look for germs and discover the germ theory for illness. That a heavy object and a light object fall at the same speed (e.g. in a vacuum, even a feather) could be attributed divine significance, and we wouldn’t revise our theories on gravity… We could look at the strange orbits of planets in our geocentric model for the universe, constructing ever-more complicated epicycle theories in order to fit the ever-more curious and inexplicable observations, because we believe God says the Earth is the centre of the universe and everything must therefore rotate around it. Or we might conclude the orbits are so intricate and utterly bizarre or silly-seeming, because “God is shuffling the planets around” to prove omnipotence.
Why? Because we selfishly need it in order to achieve some sense of wonder? Some sense of marvel at God’s creation? Isn’t it that much more marvellous and wonderful when we can comprehend how the orbits really work, how the earth rotates around the sun despite it feeling like we’re “standing still”? Eventually coming up with the remarkable theory of relativity by which we comprehend the utter marvellousness of a universe that has no centre, by which we can construct a Global Positioning System that requires taking into account how space and time warps near large mass and at speed? By which we can discover the source of illness and cure it with medicine? By which we can discover penicillin and cure disease? Create vaccinations against polio? Do you think Jesus would disapprove of us healing the sick?! WTF…
Methodological Naturalism is an absolute necessity in practising science, we would not have gotten this far if we didn’t embrace it. It is not about trying to push God out of the picture, it is merely about seeking greater understanding of this marvellous creation.
More Material: my old post titled What is Science? — I may want to revise it some time, but in the mean time, I believe you may find it enlightening.