How to beat a presupp at their own game

[Belacqua]

He's wrong.  Scientific theories don't control phenomena, they describe them. We change scientific theories not because we are changing phenomena but because we are finding moreaccurate ways to describe them.  Gravity didn't change when we switched from Newtonian equations to Einstein's relativity, just our understanding of it.

I don't think anyone is arguing that a change in theory leads to a change in nature. 

The argument, as I understand it, is that we have no way to explain why nature behaves consistently. (We call these consistencies "laws," but I agree that's misleading.) 

In actual fact, your interlocutor describes in his god centric system exactly the kind of gravity changing system he derides.  If god controls gravity, what is there to stop him from deciding, on a whim, to reverse its effects in the morning?

I suspect that they would agree: if God wanted to change everything he could. 

Their point is that because nature doesn't change overall, and its consistencies remain, there must be (in their view) something which holds things to be consistent. And that thing which holds things consistent is God. 

They have no trouble with the fact that our understanding of nature improves. The Copernican Revolution doesn't affect this at all. This is a metaphysical argument, not a scientific one. They have a metaphysical argument to say that the actual consistencies of nature, and in fact its simple existence, is held in place by something very basic, not in itself a physical object. It is a Ground of Being. 

Another way of thinking of it is as the end of the chain of questions "what is necessary for X to exist?" 

So "what is necessary for the sun to exist?"
"hydrogen, etc." 
"What is necessary for hydrogen to exist?"
"subatomic particles, etc." 
"What is necessary for those subatomic particles to exist?" 
"Space/time." 
"What is necessary for space/time to exist?"
"The Ground of Being -- existence itself" (which for them is God)