Each of the Five Ways concludes to the existence of God since, for St. Thomas, each concluded to some supernatural cause. This was possible for him since he had a more definite idea of nature than we do. He started with nature defined as mobile being and so, for example, as soon as he concluded to an immobile mover in the First Way he found a supernatural mover of natural things, which counts as some sort of god on anyone’s account of the matter. Likewise, he started with an idea of nature as acting for an end, and so in concluding to a separate intelligence that makes this happen in the Fifth Way, he had concluded to a supernatural intelligence that moved natural things, which again seems to satisfy anyone’s account of what a god is, or of something divine.
As might be clear by now, one way to avoid the confusions on this premise might be to translate “deus” as “a god” or just “a divinity”. English makes a sharp and very important division between “God” and “a god” which the Latin “deus” simply does not make. There was never a convention in St. Thomas’s time to see the capitalization of the word as changing its meaning.
But this translation shift would only take us so far. The problem seems to be more that we’re reticent to set an ontological limit on way nature is. We seem to want to define it with respect to our method of understanding, i.e. nature is whatever “science” can understand. But this simply shifts the problem since no one is quite sure what the limits placed on science are either, and so we have no idea what it would mean to conclude to a being that falls outside of its purview.
And so it seems that the problem with cosmological arguments is that we have no clear idea of what the natural is and so have no idea what would count as the supernatural. One problem is that mathematics has become so integral to our understanding of nature that we see it as somehow constitutive of it, and so any idea of nature would have to see it as an object combining what STA called both sensible and intelligible matter, but no one has any idea of what a hybrid of these would look like. It also keeps us from being able to just say that nature is the sensible world, which would allow us to define it as Aristotle did.
So what would we say? Is nature whatever interacts with a cognitive organ, either directly (by, say, hitting an eye) or one of its instruments (say, an x-ray)? But don’t we just mean a physical organ, and thus we end up assuming we know what the natural or physical are?
This is why I think that nature has to be seen as the interactive: both that which acts by interacting (i.e. in a system) and that which causes knowledge by interacting with the knower (i.e. in such a way as to change and be affected by the subject which knows. The eye and the photo-plate stop the path of the photon, the hand and thermometer affect the temperature of what they touch.) This might lead us back to Aristotle’s idea of nature (my guess is that it would) but it would give us a point of departure to get a cosmological argument off the ground.